A multilayer magnetic core for high-frequency magnetic integrated devices and a method for manufacturing the same

Abstract

A multilayer magnetic core for high-frequency magnetic integrated devices and a preparation method thereof, the multilayer magnetic core comprising a plurality of soft magnetic alloy layers and a plurality of high-resistivity regulation layers arranged alternately along a thickness direction; the soft magnetic alloy layer is a soft magnetic metal alloy layer containing at least one of iron, cobalt and nickel formed by electrochemical deposition; the high-resistivity regulation layer is a surface high-resistance modification layer formed in situ after the surface of the soft magnetic alloy layer is electrochemically regulated by reverse pulse or positive-negative combined pulse; the resistivity of the high-resistivity regulation layer is higher than that of the main body of the soft magnetic alloy layer, for increasing the interlayer resistance between adjacent soft magnetic alloy layers and weakening the continuous eddy current transmission path. The present application can solve the problems of large eddy current loss, quality factor decline and effective magnetic permeability attenuation of the existing electroplated soft magnetic metal magnetic core at high frequency. The preparation method of the multilayer magnetic core enables the soft magnetic metal layer and the high-resistivity regulation layer to be continuously formed in the same electroplating system, thereby reducing the process complexity and manufacturing cost.

Description

Technical Field

[0001] This invention belongs to the technical fields of magnetic thin film materials, micro / nano manufacturing, electrochemical deposition, and power management devices. Specifically, it relates to a multilayer magnetic core for high-frequency magnetic integrated devices and its preparation method. In particular, it relates to a multilayer magnetic core with an alternating stacked structure of soft magnetic metal layer and high resistivity control layer formed in the same electrodeposition system by electrochemical pulse modulation, which is suitable for integrated magnetic devices. Background Technology

[0002] With the rapid development of artificial intelligence chips, high-performance processors, wearable devices, and mobile terminals, electronic systems are placing higher demands on power management modules. Power management systems not only need to achieve high-efficiency voltage conversion but also meet requirements such as high power density, fast transient response, miniaturization, low loss, and high integration. In power management chips, inductors, as key passive components for energy storage and filtering, directly affect voltage conversion efficiency, output ripple, transient response, and system size. Traditional discrete inductors typically have high inductance values ​​and good current-carrying capacity, but their large size makes it difficult to meet the requirements of near-load power supply and on-chip / in-package integration for advanced chips. Therefore, integrating inductors with chips, packaging substrates, or interposers has become an important development direction for high-frequency power management systems.

[0003] To improve the inductance density of integrated inductors, soft magnetic core materials are typically introduced. Compared to air-core inductors, magnetic core inductors can achieve higher inductance values ​​within the same area, which is beneficial for reducing device size and increasing the power density of power modules. However, under high-frequency operating conditions, eddy current losses are easily generated inside the soft magnetic metal core. Especially when the core thickness is large, the operating frequency is high, or the core resistivity is low, the alternating magnetic field will induce circulating currents in the core, leading to increased core losses, decreased quality factor, and decreased effective permeability, ultimately limiting the application of the device in high-frequency power conversion scenarios. To reduce core eddy current losses, existing technologies typically employ the following approaches: First, using high-resistivity magnetic materials, such as ferrite, amorphous magnetic materials, or composite magnetic materials. However, some high-resistivity magnetic materials have low saturation magnetic flux density, making it difficult to meet the high saturation magnetic flux density requirements of high-current-density power converters; simultaneously, some materials have poor micro / nano fabrication compatibility, which is not conducive to on-chip or package integration. Second, a multilayer magnetic thin-film structure is employed, which involves alternating stacking of magnetic metal layers with insulating or high-resistivity layers to cut off eddy current paths. This method effectively reduces eddy current losses in the thickness direction of the magnetic core and is an important design concept for high-frequency soft magnetic thin-film cores. However, existing multilayer magnetic films typically rely on processes such as vacuum sputtering, evaporation, atomic layer deposition, or chemical vapor deposition for fabrication. For thicker magnetic cores, repeated deposition of magnetic and insulating layers is required, resulting in long process cycles, high equipment costs, and low deposition rates, limiting their application in large-area, thick-film, and high aspect ratio structures. Third, soft magnetic metal cores are fabricated using electroplating. Electroplating offers advantages such as high deposition rates, low costs, adjustable thickness, suitability for large-area wafer-level fabrication, and patterned filling, and has been widely used in micro-inductors, micro-transformers, MEMS devices, and packaged interconnect structures. However, traditional electroplated soft magnetic metal layers are typically continuous conductive metal films with relatively low resistivity, which still easily lead to significant eddy current losses at high frequencies. To fabricate multilayer magnetic cores using electroplating, existing methods typically require the introduction of an additional insulating or high-resistivity layer between each magnetic layer. This can be achieved through methods such as sputtering, spin coating, oxidation, deposition of a dielectric layer, or multiple seed layer preparations. These methods result in complex processes, difficulty in controlling the interlayer interfaces, and increased processing costs and risks.

[0004] Therefore, there is an urgent need for a new multilayer magnetic core and its fabrication method that can maintain the advantages of high saturation magnetic induction, high deposition rate and low cost of electroplated soft magnetic metal cores, while suppressing high-frequency eddy current losses through layered structure. At the same time, the method should avoid the complicated process of multiple vacuum deposition and multiple seed layer preparation, and be able to realize the continuous construction of soft magnetic layer and high resistivity control layer in the same electrodeposition system, so as to be suitable for large-area, low-cost and scalable manufacturing of high-frequency magnetic integrated devices. Summary of the Invention

[0005] In view of the shortcomings of existing technologies, this invention provides a multilayer magnetic core for high-frequency magnetic integrated devices and its fabrication method, to solve the problems of high eddy current loss, decreased quality factor, and attenuation of effective permeability in existing electroplated soft magnetic metal cores at high frequencies. The multilayer magnetic core fabrication method provided by this invention eliminates the need for multiple vacuum sputtering processes, repeated seed layer preparation, and frequent changes in the process environment. This allows the soft magnetic metal layer and the high resistivity control layer to be continuously formed in the same electrodeposition system, thereby reducing process complexity and manufacturing costs.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: In a first aspect, a multilayer magnetic core for high-frequency magnetic integrated devices includes multiple soft magnetic alloy layers and multiple high resistivity control layers alternately arranged along the thickness direction. The soft magnetic alloy layer is a soft magnetic metal alloy layer containing at least one element selected from iron, cobalt, and nickel, formed by electrochemical deposition; The high resistivity modulation layer is a surface high resistivity modification layer formed in situ on the surface of the soft magnetic alloy layer after electrochemical modulation by reverse pulse or a combination of forward and reverse pulses. The resistivity of the high resistivity control layer is higher than that of the soft magnetic alloy layer body, which is used to increase the interlayer resistance between adjacent soft magnetic alloy layers and weaken the continuous eddy current transmission path.

[0007] Preferably, the soft magnetic alloy layer includes one or more of the following: iron-based soft magnetic alloy layer, cobalt-based soft magnetic alloy layer, nickel-based soft magnetic alloy layer, iron-cobalt-based soft magnetic alloy layer, iron-nickel-based soft magnetic alloy layer, cobalt-nickel-based soft magnetic alloy layer, or iron-cobalt-nickel-based soft magnetic alloy layer.

[0008] Preferably, the soft magnetic alloy layer also contains one or more elements selected from phosphorus, boron, carbon, nitrogen, silicon, molybdenum, tungsten, copper, and chromium.

[0009] Preferably, the high resistivity control layer includes a non-metallic element enrichment region, an amorphous region, a nanocrystalline-amorphous composite region, an oxidation-modified region, a phosphating-modified region, a boronizing-modified region, or a combination of the above regions.

[0010] Preferably, the content of iron, cobalt, or nickel in the high resistivity control layer is lower than the content of the corresponding element in the main region of the soft magnetic alloy layer.

[0011] Preferably, the content of phosphorus, boron, carbon, nitrogen, or silicon in the high resistivity control layer is higher than the content of the corresponding elements in the main region of the soft magnetic alloy layer.

[0012] Secondly, a method for fabricating a multilayer magnetic core for high-frequency magnetic integrated devices includes the following steps: S1, Obtain a substrate and form a conductive substrate or conductive seed layer on the substrate; S2, the substrate is placed in an electrodeposition solution containing soft magnetic metal ions; S3, apply a positive electrodeposition waveform to the substrate to deposit a soft magnetic alloy layer on the conductive substrate or conductive seed layer; S4. Without replacing the electrodeposition solution, an electrochemical modulation waveform of a reverse pulse or a combination of forward and reverse pulses is applied to cause electrochemical high resistivity modulation on the surface of the soft magnetic alloy layer, thereby forming a high resistivity modulation layer in situ on the surface of the soft magnetic alloy layer. S5. Repeat steps S3 and S4 to form a multilayer magnetic core in which the soft magnetic alloy layer and the high resistivity control layer are alternately arranged along the thickness direction.

[0013] Preferably, step S3 includes: the first electrodeposition waveform is a forward DC electrodeposition; a soft magnetic alloy layer is deposited on a conductive substrate or a conductive seed layer using an anode plate; step S4 includes: by directly changing the electrode polarity of the substrate and the anode plate, the surface of the soft magnetic alloy layer undergoes anodic dissolution and composition reconstruction, thereby forming a high resistivity control layer.

[0014] Preferably, step S3 includes: the soft magnetic alloy layer is formed by forward deposition; step S4 includes: selective anodic dissolution, metal element depletion and non-metal element relative enrichment occur on the surface of the soft magnetic alloy layer by directly applying a reverse pulse or a combination waveform of forward short pulse and reverse short pulse, thereby forming a high resistivity control layer.

[0015] Preferably, the thickness of the soft magnetic alloy layer is controlled by adjusting the current density, on-time, off-time, number of pulses, or deposition period of the forward electrodeposition waveform; the thickness, composition, resistivity, or continuity of the high resistivity control layer is controlled by adjusting the reverse current density, reverse potential, on-time, off-time, number of pulses, or control period of the reverse pulse, bidirectional pulse, or combined forward and reverse pulse electrochemical control waveform.

[0016] Compared with the prior art, the beneficial effects of the present invention are reflected in: 1. By using an alternating stacking structure of soft magnetic metal layers and high resistivity control layers, the eddy current path inside the magnetic core is effectively weakened. Under the influence of a high-frequency alternating magnetic field, closed eddy currents are easily formed inside a continuous metal core. This invention introduces a high resistivity control layer between adjacent soft magnetic metal layers, which can increase the interlayer resistance, limit the expansion of eddy currents in the thickness direction and local in-plane directions, thereby reducing eddy current losses and improving the effective permeability and quality factor at high frequencies.

[0017] 2. Balancing high magnetic performance and low loss The soft magnetic metal layer provides high saturation magnetic flux density and high permeability, while the high resistivity control layer primarily serves to block eddy current paths. Compared to solutions that use materials with high resistivity but low saturation magnetic flux density throughout, this invention is more advantageous in meeting the core saturation characteristics requirements of high current density power management devices.

[0018] 3. Avoids the dependence on complex vacuum deposition processes inherent in traditional multilayer magnetic films. Existing soft magnetic / insulating multilayer films typically require repeated deposition of magnetic and dielectric layers, resulting in complex and costly processes. This invention utilizes electrochemical waveform modulation to form a high resistivity control layer within the same electrodeposition system, eliminating the need for multiple sputtering seed layers or repeated process environment transfers.

[0019] 4. Suitable for the fabrication of thick-film, large-area, and patterned magnetic cores. Electrochemical deposition offers advantages such as high deposition rate, adjustable thickness, low cost, good uniformity of three-dimensional structure coverage, and suitability for wafer-level processing. This invention can be used to fabricate multilayer magnetic cores with thicknesses ranging from micrometers to hundreds of micrometers, and is suitable for on-chip inductors, packaged integrated inductors, and interposer integrated magnetic devices.

[0020] 5. Layer thickness and resistivity can be precisely controlled via pulse parameters.

[0021] By adjusting the forward deposition current density, forward conduction time, number of forward pulses, reverse current density, reverse conduction time, number of reverse pulses, and pulse period, the thickness of the soft magnetic metal layer, the thickness of the high resistivity control layer, the interface composition, and the interlayer resistance can be adjusted, thereby enabling the designability of the magnetic core performance.

[0022] 6. It has strong adaptability to materials and devices.

[0023] This method is applicable not only to on-chip thin-film inductors, but also to inductors embedded in package substrates, stripline inductors, solenoid inductors, coupled inductors, miniature transformers, and magnetic core structures in high-frequency power management modules.

[0024] Figure Labels Figure 1 This is a schematic diagram of the cross-sectional structure of the multilayer magnetic core of the present invention.

[0025] Figure 2 This is a schematic diagram comparing the eddy current paths in a traditional continuous metal magnetic core and the multilayer magnetic core of this invention.

[0026] Figure 3 This is a schematic diagram of the process flow for the preparation method of the present invention.

[0027] Figure 4 This is a current-time diagram showing the alternating application of forward deposition and reverse pulse modulation waveforms in this invention.

[0028] Figure 5 This is a schematic diagram illustrating the mechanism of forming a high resistivity control layer through forward deposition and reverse pulse modulation in this invention.

[0029] Figure 6 This is a schematic diagram illustrating the mechanism of forming a high resistivity control layer through forward deposition and forward and reverse pulse modulation in this invention.

[0030] Figure 7 This is a schematic diagram illustrating the mechanism of forming a high resistivity control layer through forward pulse deposition and forward and reverse pulse modulation in this invention.

[0031] Figure 8 This is a schematic diagram of the multilayer magnetic core of the present invention applied to a thin-film inductor.

[0032] Among them, 101 is the substrate; 102 is the conductive seed layer; 100 is the multilayer magnetic core; 110 is the soft magnetic alloy layer; 120 is the high resistivity control layer; 210 is the conducting winding; and 220 is the insulating dielectric layer. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. It should be understood that the structures, proportions, sizes, etc., drawn in the accompanying drawings of this specification are only used to complement the content disclosed in the specification, so as to enable those skilled in the art to understand and read, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modification to the structure, change in the proportional relationship, or adjustment of the size should still fall within the scope of the technical content disclosed in the present invention, provided that it does not affect the effects and objectives that the present invention can produce.

[0034] Example 1: like Figure 1 As shown, this embodiment provides a multilayer magnetic core 100 for high-frequency magnetic integrated devices. The multilayer magnetic core 100 is disposed on a substrate 101. A conductive seed layer 102 may be disposed on the surface of the substrate 101. The multilayer magnetic core body is disposed above the conductive seed layer 102.

[0035] The multilayer magnetic core body includes multiple soft magnetic alloy layers 110 and multiple high resistivity control layers 120. The soft magnetic alloy layers 110 and the high resistivity control layers 120 are alternately arranged along the thickness direction.

[0036] The soft magnetic alloy layer 110 is a soft magnetic metal alloy layer formed by electrochemical deposition, and its main function is to provide a high-permeability magnetic flux channel. The soft magnetic alloy layer 110 can be an iron-based, cobalt-based, nickel-based, iron-cobalt-based, iron-nickel-based, cobalt-nickel-based, or iron-cobalt-nickel-based soft magnetic alloy layer. The soft magnetic alloy layer 110 may also contain one or more elements selected from phosphorus, boron, carbon, nitrogen, silicon, molybdenum, tungsten, copper, and chromium to improve soft magnetic properties, resistivity, amorphous formation ability, stress state, or corrosion resistance.

[0037] The high resistivity control layer 120 is located between two adjacent soft magnetic alloy layers 110. The high resistivity control layer 120 is not an independently deposited polymer layer or oxide insulating layer, but a surface high resistivity modification layer formed by electrochemical control of the upper surface of the lower soft magnetic alloy layer 110 through electrode polarity reversal, reverse pulse, or a combination of forward and reverse pulses.

[0038] The high resistivity control layer 120 has a higher resistivity than the soft magnetic alloy layer 110. It may include non-metallic element enrichment regions, amorphous regions, nanocrystalline-amorphous composite regions, or oxidation / phosphating / boration modified regions.

[0039] Because the high-resistivity control layer 120 is disposed between adjacent soft magnetic alloy layers 110, it can increase the interlayer resistance, weaken the continuous eddy current path inside the magnetic core, and confine the eddy currents generated under high-frequency alternating magnetic fields to a smaller region, such as... Figure 2 As shown, this reduces eddy current losses in the magnetic core.

[0040] Example 2: like Figure 3 As shown, this embodiment provides a method for fabricating a multilayer magnetic core, including the following steps.

[0041] Step S1: Substrate preparation Substrates are provided. Substrates can be silicon substrates, glass substrates, ceramic substrates, organic packaging substrates, metal foils, flexible substrates, wafer-level packaging substrates, interposer substrates, or printed circuit board substrates.

[0042] A conductive substrate or conductive seed layer is formed on the surface of a substrate. The conductive seed layer can be formed by sputtering, evaporation, electroless plating, electroplating, or metal foil attachment. The conductive seed layer may include one or more of copper, titanium, chromium, tantalum, tungsten, nickel, gold, platinum, molybdenum, or alloys thereof.

[0043] In a preferred embodiment, the substrate is a silicon wafer, and the conductive seed layer is a titanium / copper composite seed layer. The titanium layer is used to improve adhesion, and the copper layer is used to provide conductive channels for electrodeposition.

[0044] Step S2: Preparation of electrodeposition solution The electrodeposition solution may contain one or more of iron ions, cobalt ions, and nickel ions, and may further contain complexing agents, buffers, conductive salts, stress modifiers, pH modifiers, grain refiners, or sources of non-metallic elements.

[0045] Non-metallic elements can be used to introduce elements such as phosphorus, boron, carbon, nitrogen, and silicon into soft magnetic metal layers, thereby improving soft magnetic properties or increasing resistivity.

[0046] The pH of the electrodeposition solution can be adjusted according to the material system, for example, from 1 to 7. The electrodeposition temperature can be from 10°C to 90°C.

[0047] Step S3: Deposition of soft magnetic metal layer The substrate is placed in an electrodeposition solution containing soft magnetic metal ions, and a first electrodeposition waveform is applied to deposit a soft magnetic metal layer on a conductive substrate or conductive seed layer.

[0048] The first electrodeposition waveform can be a DC waveform, a constant current waveform, a constant potential waveform, a unidirectional pulse waveform, or a combination thereof. The main function of the first electrodeposition waveform is to form a soft magnetic metal layer with high permeability and high saturation magnetic induction.

[0049] In one embodiment, the first electrodeposition waveform is a forward constant current deposition, with a forward average current density of 0.1 mA / cm². 2 Up to 200 mA / cm 2 .

[0050] In another embodiment, the first electrodeposition waveform is a unidirectional pulse deposition, with a forward conduction time of 0.01 ms to 10 s and a forward turn-off time of 0 to 10 s. The number of forward pulses is determined according to the thickness of the target soft magnetic metal layer.

[0051] The thickness, composition, and soft magnetic properties of the soft magnetic metal layer can be controlled by adjusting the electroplating bath temperature, pH value, deposition current density, deposition time, pulse duty cycle, and current efficiency.

[0052] Step S4: Formation of high resistivity control layer After the soft magnetic metal layer is deposited, the sample is not removed or the electrodeposition environment is not changed. Instead, a second electrochemical modulation waveform is applied directly to electrochemically modulate the surface of the soft magnetic metal layer.

[0053] The second electrochemical modulation waveform can include a reverse pulse, a combination of forward and reverse pulses, a step pulse, or a non-periodic pulse.

[0054] During the second electrochemical regulation process, at least one of the following changes occurs on the surface of the soft magnetic metal layer: 1. Some metallic elements undergo selective electrolysis; 2. Relative enrichment of nonmetallic or near-metallic elements occurs; 3. A high-resistivity phase is formed on the surface; 4. The surface crystal structure transforms from a crystalline state to an amorphous state or a nanocrystalline-amorphous composite structure; 5. Surface roughness, composition, or defect state can be controlled; 6. A control layer with a resistivity higher than that of the main body of the soft magnetic metal layer is formed on the surface.

[0055] Thus, a high resistivity modulation layer is formed on the surface of the soft magnetic metal layer.

[0056] In a preferred embodiment, the second electrochemical modulation waveform is a reverse pulse waveform. The average reverse current density is 0.1 mA / cm². 2 Up to 500 mA / cm 2 The reverse conduction time is 0.01 ms to 10 s, and the reverse turn-off time is 0 to 10 s.

[0057] In another preferred embodiment, the second electrochemical modulation waveform is an alternating waveform of forward short pulses and reverse short pulses. The forward short pulses are used to replenish the deposition and maintain interfacial activity, while the reverse short pulses are used to selectively electrolyze the surface metal elements, thereby obtaining a high resistivity modulation layer.

[0058] Step S5: Repeated Deposition and Regulation Repeat steps S3 and S4 to obtain a multilayer magnetic core with alternating stacks of soft magnetic metal layers and high resistivity control layers.

[0059] The number of repetition cycles can be determined based on the total thickness of the target magnetic core and the target high-frequency performance. For example, when the thickness of a single soft magnetic metal layer is 200 nm and the thickness of the high resistivity modulation layer is 10 nm, several repetition cycles can be performed to prepare a multilayer magnetic core with a total thickness of several micrometers to tens of micrometers.

[0060] Step S6: Post-processing After obtaining the multilayer magnetic core, it can be patterned, de-adhesive removed, etched, insulated, planarized, heat-treated, magnetically annealed, or packaged and integrated according to the device requirements.

[0061] In one embodiment, the multilayer magnetic core is subjected to magnetic field annealing to induce magnetic anisotropy, reduce coercivity, and improve high-frequency permeability.

[0062] In another embodiment, the surface of the multilayer magnetic core is insulated to prevent short circuits between the subsequent conductor layer and the magnetic core.

[0063] Example 3: A method for fabricating multilayer magnetic cores based on electrode polarity reversal This embodiment provides a method for fabricating multilayer magnetic cores based on electrode polarity reversal. This method involves directly changing the polarity of the working electrode and the counter electrode after the soft magnetic alloy layer has been deposited in the forward DC direction. This causes anodic dissolution, compositional reconstruction, or relative enrichment of high-resistivity elements on the surface of the deposited soft magnetic alloy layer, thereby forming a high-resistivity control layer on the surface of the soft magnetic alloy layer.

[0064] Specifically, a substrate with a conductive seed layer is first provided and placed in an electrodeposition solution containing soft magnetic metal ions as the workpiece to be plated. In the forward deposition stage, the workpiece to be plated is connected as the cathode and the anode plate is connected as the anode. A forward DC current or a forward DC potential is applied to reduce and deposit the metal ions in the electrodeposition solution on the surface of the workpiece to form a soft magnetic alloy layer.

[0065] After the soft magnetic alloy layer reaches the predetermined thickness, forward DC deposition is stopped. Subsequently, the electrode polarity of the workpiece to be plated is directly reversed with that of the anode plate, turning the workpiece, which was originally the cathode, into the anode, and the anode plate, which was originally the anode, into the cathode. At this time, a reverse DC current or a reverse DC potential is applied to cause anodic electrochemical treatment on the surface of the deposited soft magnetic alloy layer.

[0066] During this reverse polarity treatment, some metal elements on the surface of the soft magnetic alloy layer undergo electrolysis, especially iron, cobalt, nickel and other metal components may undergo anodic dissolution to varying degrees; at the same time, non-metallic or quasi-metallic elements such as phosphorus, boron, carbon, nitrogen, silicon and other non-metallic or quasi-metallic elements may be relatively enriched on the surface, or the surface area may undergo oxidation, phosphating, amorphization, roughening or compositional reconstruction, thereby forming a high resistivity control layer with a resistivity higher than that of the main area of ​​the soft magnetic alloy layer.

[0067] After completing one reverse polarity treatment, the workpiece to be plated is restored to the cathode, and the anode plate is restored to the anode, and the next cycle of forward DC deposition continues. By repeating the process of "forward DC deposition of soft magnetic alloy layer - electrode polarity reversal to form high resistivity control layer", a multilayer magnetic core in which soft magnetic alloy layer and high resistivity control layer are alternately arranged along the thickness direction can be obtained.

[0068] In this embodiment, the current density during the forward DC deposition stage can be 0.1 mA / cm². 2 Up to 200 mA / cm 2 Preferably 1 mA / cm 2 Up to 50 mA / cm 2 The reverse current density during the reverse polarity processing stage can be 0.1 mA / cm². 2 Up to 500mA / cm 2 Preferably 1 mA / cm 2 Up to 100 mA / cm 2The forward DC deposition time can be determined based on the thickness of the target soft magnetic alloy layer, while the reverse polarity processing time can be from 0.1 s to 300 s, preferably from 1 s to 60 s.

[0069] It should be noted that, due to the difficulty in precisely controlling the current distribution, edge effect, solution diffusion layer state, and surface electrolysis rate during the reverse processing, the resulting high resistivity control layer may exhibit some inhomogeneity in terms of thickness, composition, and continuity. However, this method has low equipment requirements and is simple to operate, enabling high resistivity treatment of the soft magnetic alloy layer surface without introducing an additional independent insulating or polymer layer; therefore, it remains an optional embodiment of the present invention.

[0070] Example 4: Periodic multilayer magnetic core based on forward deposition and reverse pulse modulation This embodiment provides a method for fabricating a periodic multilayer magnetic core, wherein the applied current waveform is as follows: Figure 4 As shown, the formation mechanism of the high resistivity control layer is as follows: Figure 5 As shown.

[0071] First, a titanium / copper seed layer is formed on the surface of a silicon substrate. Then, the substrate is placed in a soft magnetic alloy electrodeposition solution.

[0072] A positive electrodeposition waveform is applied to deposit a first soft magnetic alloy layer. The thickness of this soft magnetic alloy layer is 50 nm to 2 μm.

[0073] Subsequently, a reverse pulse electrochemical modulation waveform is applied to cause slight selective electrolysis and etching of the metal on the surface of the first soft magnetic alloy layer, forming a high resistivity modulation layer with a thickness of 2 nm to 100 nm.

[0074] Then, a positive electrodeposition waveform is applied again to deposit a second soft magnetic metal alloy layer on the surface of the high resistivity control layer. Since the high resistivity control layer is not a completely insulating thick dielectric layer, but a high resistivity control layer with certain conductivity or local conduction characteristics, subsequent electrodeposition can still be carried out without re-sputtering the seed layer.

[0075] By repeating the above process, a multi-period soft magnetic metal layer / high resistivity control layer stack structure can be formed.

[0076] The key advantage of this embodiment is that the high resistivity control layer can increase the interlayer resistance and suppress eddy currents, but still allow the subsequent electrodeposition process to continue, thus achieving both the goals of "continuous electrochemical preparation" and "high-frequency eddy current suppression".

[0077] It should be noted that, in this embodiment, after the soft magnetic alloy layer is formed by forward electrodeposition, if a reverse pulse is directly applied for high resistivity control, although anodic electrolysis, depletion of metal elements, and relative enrichment of non-metal elements can occur on the surface of the soft magnetic alloy layer, thereby forming a high resistivity control layer, the reverse pulse will also have a certain electrolytic or consumption effect on the deposited soft magnetic alloy layer. During the off-time, the deposited soft magnetic alloy layer will also be etched due to the acidic plating solution environment. Especially when the reverse current density is large, the reverse conduction time is long, or the number of reverse pulses is large, the deposited soft magnetic alloy layer may experience local over-electrolysis and etching, surface roughening, void formation, layer thinning, or even local damage, making it difficult to accurately control the effective thickness of the soft magnetic alloy layer and the actual thickness of the high resistivity control layer.

[0078] Example 5: A method for fabricating a high-resistivity modulation layer based on a combination of forward and reverse short pulses. To address the issues of excessive consumption and uncontrollable thickness of the soft magnetic alloy layer caused by direct reverse pulse modulation in Example 4, this embodiment provides a method for fabricating a high resistivity modulation layer using a combination of forward short pulses and reverse short pulses. The applied current waveform is as follows: Figure 6 As shown.

[0079] After the soft magnetic metal layer deposition is completed, several sets of forward and reverse short pulses are applied. Each set of pulses includes: Positive short pulses: used to deposit very thin surface modulation layers on the surface of soft magnetic metal layers; Short pause: used for diffusion layer recovery and redistribution of interfacial ion concentration; Reverse short pulse: used for selective dissolution of some metal elements on the surface; Pause again: Used to stabilize the interface state.

[0080] Through multiple cycles, a high-resistivity control layer is gradually formed on the surface of the soft magnetic metal layer, characterized by a relative enrichment of high-resistivity elements, a relative depletion of metal elements, or a structure of amorphization.

[0081] In this embodiment, the conduction time of the forward short pulse can be from 0.01 ms to 100 ms, and the conduction time of the reverse short pulse can be from 0.01 ms to 100 ms. The current density of the forward and reverse short pulses can be adjusted according to the deposition system and the target layer thickness.

[0082] Compared with simple reverse pulses, the combination of forward short pulses and reverse short pulses is beneficial to reducing film roughness, peeling or interface defects caused by excessive dissolution, while also helping to improve the continuity and repeatability of high resistivity control layers.

[0083] Example 6: A method for fabricating multilayer magnetic cores based on forward pulse deposition and forward / reverse pulse modulation, wherein the applied current waveform is as follows: Figure 7As shown.

[0084] This embodiment provides a method for fabricating multilayer magnetic cores based on forward pulse deposition and forward / reverse pulse modulation. Compared with the method of forward DC deposition of soft magnetic alloy layers, this embodiment uses forward pulse electrodeposition to fabricate soft magnetic alloy layers, and further uses a combination of forward short pulses and reverse short pulses to modulate the surface of the soft magnetic alloy layer to improve the controllability of the thickness, composition, and high resistivity modulation layer interface of the soft magnetic alloy layer.

[0085] Specifically, a substrate with a conductive seed layer is first provided, and the substrate is placed in an electrodeposition solution containing soft magnetic metal ions as the workpiece to be plated. During the soft magnetic alloy layer deposition stage, the workpiece to be plated is used as the cathode, and the anode plate is used as the anode. A positive pulse electrodeposition waveform is applied, causing the metal ions in the electrodeposition solution to be periodically reduced and deposited on the surface of the workpiece, thereby forming a soft magnetic alloy layer.

[0086] In forward pulse electrodeposition, the forward pulse on-phase is used to deposit soft magnetic alloys, while the forward pulse off-phase is used to alleviate concentration polarization on the electrode surface, allowing the metal ion concentration near the electrode / electrolyte interface to recover to some extent. Compared with continuous DC deposition, forward pulse deposition is beneficial for improving the compositional uniformity, grain size, surface smoothness, and film density of the soft magnetic alloy layer, and also helps to reduce deposition stress and the risk of localized burn-off.

[0087] Once the soft magnetic alloy layer reaches the predetermined thickness, the high resistivity control layer formation stage begins. In this stage, a combination of forward and reverse short pulse waveforms is applied. The forward short pulse is used to perform minor compensation deposition on the surface of the soft magnetic alloy layer, maintain interfacial activity, or repair local defects caused by reverse dissolution. The reverse short pulse is used to selectively anodicly dissolve some metal elements on the surface of the soft magnetic alloy layer, causing relative enrichment of non-metallic or quasi-metallic elements such as phosphorus, boron, carbon, nitrogen, and silicon on the surface, or to cause amorphization, oxidation, phosphating, borylation, or compositional reconstruction on the surface, thereby forming a high resistivity control layer with a resistivity higher than that of the main region of the soft magnetic alloy layer.

[0088] In one specific embodiment, the forward average current density of the forward pulse electrodeposition waveform is 0.1 mA / cm². 2 Up to 200 mA / cm 2 Preferably 1 mA / cm 2 Up to 50 mA / cm 2 The forward conduction time is 0.01 ms to 10 s, preferably 0.1 ms to 100 ms; the forward turn-off time is 0.01 ms to 10 s, preferably 0.1 ms to 500 ms. By adjusting the forward pulse current density, conduction time, turn-off time, duty cycle, and number of pulses, the deposition rate, monolayer thickness, and film density of the soft magnetic alloy layer can be controlled.

[0089] In one specific embodiment, the forward short pulse-reverse short pulse combined waveform includes at least one forward short pulse and at least one reverse short pulse. The conduction time of the forward short pulse can be from 0.01 ms to 1000 ms, preferably from 0.1 ms to 100 ms; the conduction time of the reverse short pulse can be from 0.01 ms to 1000 ms, preferably from 0.1 ms to 100 ms. The reverse average current density can be 0.1 mA / cm². 2 Up to 500 mA / cm 2 Preferably 1 mA / cm 2 Up to 100 mA / cm 2 The forward and reverse short pulses can be applied alternately in the manner of "one forward short pulse - one reverse short pulse", or in combination in the manner of "multiple forward short pulses - one reverse short pulse" or "one forward short pulse - multiple reverse short pulses".

[0090] By repeating the process of "depositing a soft magnetic alloy layer with a forward pulse and forming a high resistivity control layer by combining a forward short pulse and a reverse short pulse", a multilayer magnetic core in which the soft magnetic alloy layer and the high resistivity control layer are alternately arranged along the thickness direction can be obtained.

[0091] Compared to applying a single reverse pulse directly after the soft magnetic alloy layer is deposited, this embodiment introduces a forward short pulse to compensate for the deposition and interface repair process. This reduces excessive etching and net consumption of the deposited soft magnetic alloy layer's main structure by the reverse pulse, minimizing surface roughening, porosity, and localized over-dissolution. Consequently, it improves the thickness controllability, interface continuity, uniformity, and periodic repeatability of the high resistivity control layer. This method is particularly suitable for high-frequency magnetic integrated devices requiring high consistency in multilayer core periodic thickness, high-frequency loss, and stability in batch fabrication.

[0092] Example 6: Gradient Multilayer Magnetic Core This embodiment provides a gradient multilayer magnetic core.

[0093] In regions near where the alternating magnetic field is strong or where eddy current losses are significant, the soft magnetic metal layer is made thinner, while the high resistivity control layer is made denser. For example, the thickness of the soft magnetic metal layer is 50 nm to 300 nm, and the thickness of the high resistivity control layer is 5 nm to 50 nm.

[0094] In areas far from high-frequency magnetic field concentration regions or main magnetic flux transmission regions, the thickness of the soft magnetic metal layer can be appropriately increased. For example, the thickness of the soft magnetic metal layer can be 300 nm to 2 μm, and the thickness of the high resistivity modulation layer can be 5 nm to 100 nm.

[0095] This gradient stacked design can reduce eddy current losses in high-loss regions while ensuring overall effective permeability and saturation magnetic induction.

[0096] Example 7: Application of multilayer magnetic cores in thin-film inductors like Figure 8 As shown, this embodiment provides a thin-film inductor, including a substrate, a bottom insulating layer, a conductor winding, an interlayer insulating layer, and a multilayer magnetic core.

[0097] Multilayer magnetic cores are located above, below, to the side of, or within the area surrounded by conductor windings to enhance magnetic flux coupling and increase inductance density.

[0098] Because a high resistivity control layer is provided in the multilayer magnetic core, the eddy current loss of the magnetic core is reduced and the quality factor of the inductor is improved when the thin film inductor operates at high frequency. The attenuation of the effective inductance value at high frequency is suppressed.

[0099] This thin-film inductor can be used in DC-DC converters, RF circuits, power management chips, on-chip power modules, or fully integrated voltage regulators.

[0100] Example 8: Post-processing and Magnetic Performance Optimization After the multilayer magnetic core is fabricated, post-processing can be performed according to the device requirements.

[0101] One post-processing method is magnetic field annealing. Annealing under certain temperature and applied magnetic field conditions can reduce the internal stress of the soft magnetic alloy layer, improve the magnetic domain structure, induce magnetic anisotropy, and reduce coercivity.

[0102] Another post-processing method is insulation coating. By covering the surface of the multilayer magnetic core with an insulating dielectric layer, short circuits between the subsequent conductor layers and the magnetic core can be prevented.

[0103] It can also perform patterning etching, chemical mechanical planarization, package interconnection, interlayer dielectric deposition, or conductor winding preparation according to the device processing flow.

[0104] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. All equivalent transformations and modifications made in accordance with the scope of the present application should be within the technical scope of the present invention.

Claims

1. A multilayer magnetic core for high-frequency magnetic integrated devices, characterized in that, It includes multiple soft magnetic alloy layers and multiple high resistivity control layers that are alternately arranged along the thickness direction; The soft magnetic alloy layer is a soft magnetic metal alloy layer containing at least one element selected from iron, cobalt, and nickel, formed by electrochemical deposition; The high resistivity modulation layer is a surface high resistivity modification layer formed in situ on the surface of the soft magnetic alloy layer after electrochemical modulation by reverse pulse or a combination of forward and reverse pulses. The resistivity of the high resistivity control layer is higher than that of the soft magnetic alloy layer body, which is used to increase the interlayer resistance between adjacent soft magnetic alloy layers and weaken the continuous eddy current transmission path.

2. The multilayer magnetic core for high-frequency magnetic integrated devices according to claim 1, characterized in that, The soft magnetic alloy layer includes one or more of the following: iron-based soft magnetic alloy layer, cobalt-based soft magnetic alloy layer, nickel-based soft magnetic alloy layer, iron-cobalt-based soft magnetic alloy layer, iron-nickel-based soft magnetic alloy layer, cobalt-nickel-based soft magnetic alloy layer, or iron-cobalt-nickel-based soft magnetic alloy layer.

3. A multilayer magnetic core for high-frequency magnetic integrated devices according to claim 2, characterized in that, The soft magnetic alloy layer also contains one or more elements selected from phosphorus, boron, carbon, nitrogen, silicon, molybdenum, tungsten, copper, and chromium.

4. A multilayer magnetic core for high-frequency magnetic integrated devices according to claim 1, characterized in that, The high resistivity control layer includes a non-metallic element enrichment region, an amorphous region, a nanocrystalline-amorphous composite region, an oxidation-modified region, a phosphating-modified region, a boronizing-modified region, or a combination of the above regions.

5. A multilayer magnetic core for high-frequency magnetic integrated devices according to claim 2, characterized in that, The content of iron, cobalt, or nickel in the high resistivity control layer is lower than the content of the corresponding elements in the main region of the soft magnetic alloy layer.

6. A multilayer magnetic core for high-frequency magnetic integrated devices according to claim 3, characterized in that, The content of phosphorus, boron, carbon, nitrogen, or silicon in the high resistivity control layer is higher than the content of the corresponding elements in the main region of the soft magnetic alloy layer.

7. A method for fabricating a multilayer magnetic core for high-frequency magnetic integrated devices, characterized in that, Includes the following steps: S1, Obtain a substrate and form a conductive substrate or conductive seed layer on the substrate; S2, the substrate is placed in an electrodeposition solution containing soft magnetic metal ions; S3, apply a positive electrodeposition waveform to the substrate to deposit a soft magnetic alloy layer on the conductive substrate or conductive seed layer; S4. Without replacing the electrodeposition solution, an electrochemical modulation waveform of a reverse pulse or a combination of forward and reverse pulses is applied to cause electrochemical high resistivity modulation on the surface of the soft magnetic alloy layer, thereby forming a high resistivity modulation layer in situ on the surface of the soft magnetic alloy layer. S5. Repeat steps S3 and S4 to form a multilayer magnetic core in which the soft magnetic alloy layer and the high resistivity control layer are alternately arranged along the thickness direction.

8. The electrochemical preparation method according to claim 7, characterized in that, Step S3 includes: the first electrodeposition waveform is a forward DC electrodeposition; a soft magnetic alloy layer is deposited on a conductive substrate or a conductive seed layer using an anode plate; Step S4 includes: by directly changing the electrode polarity of the substrate and the anode plate, the surface of the soft magnetic alloy layer undergoes anodic dissolution and composition reconstruction, thereby forming a high resistivity control layer.

9. The electrochemical preparation method according to claim 7, characterized in that, Step S3 includes: forming a soft magnetic alloy layer by forward deposition; Step S4 includes: selectively dissolving the soft magnetic alloy layer surface by directly applying a reverse pulse or a combination of forward short pulse and reverse short pulse waveform, depleting metal elements, and relatively enriching non-metal elements, thereby forming a high resistivity control layer.

10. The electrochemical preparation method according to claim 7, characterized in that, The thickness of the soft magnetic alloy layer can be controlled by adjusting the current density, on-time, off-time, number of pulses, or deposition period of the forward electrodeposition waveform; the thickness, composition, resistivity, or continuity of the high resistivity control layer can be controlled by adjusting the reverse current density, reverse potential, on-time, off-time, number of pulses, or control period of the reverse pulse, bidirectional pulse, or combined forward and reverse pulse electrochemical control waveform.

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