Inductor and method for manufacturing inductor

Abstract

Provided is an inductor in which magnetic characteristics and insulation characteristics are improved, and a method for manufacturing the inductor. An inductor 1 according to the present disclosure comprises: an element body 10 comprising a plurality of magnetic metal particles MP coated with an oxide film OL and containing the elements Fe and Si, with adjacent magnetic metal particles MP being directly bonded to each other by the oxide films OL; and a coil C that is embedded in the element body 10. The oxide film OL comprises: an inner oxide film OLi that is in contact with the surface of the magnetic metal particles MP and has the element Si as a main component; and an outer oxide film OLo that contains an easily oxidizable metal element. The content ratio of the metal element and the element Fe in the outer oxide film OLo is 0.9 atom% or greater.

Description

Inductor and method for manufacturing inductor

[0001] The present disclosure relates to an inductor and a method for manufacturing an inductor.

[0002] Patent Document 1 discloses a magnetic base comprising a plurality of metal magnetic particles and a binding part that binds the plurality of metal magnetic particles, wherein the binding part is formed of an amorphous mixture containing an oxide of at least one element selected from silicon, aluminum, chromium, magnesium, titanium, and zirconium, and carbon, the magnetic base covers at least a part of surfaces of the plurality of metal magnetic particles and includes an oxide film that does not substantially contain carbon in the film, and the binding part binds the plurality of metal magnetic particles by binding the oxide films to each other via the binding part (see claim 1 and claim 4 of Patent Document 1).

[0003] Furthermore, Patent Document 1 discloses that a resinate containing at least one element selected from silicon (Si), aluminum (Al), chromium (Cr), magnesium (Mg), titanium (Ti), and zirconium (Zr) is used as the binding part, as an example of a method for manufacturing the magnetic base, a plurality of metal magnetic particles, a resin composition and a solvent are mixed to prepare a magnetic paste, and the resin composition contains a binder resin and a resinate dissolved in the binder resin and containing at least one element selected from Si, Al, Cr, Mg, Ti, and Zr (see paragraphs

[0022] to

[0023] of Patent Document 1).

[0004] Japanese Unexamined Patent Publication No. 2021-132077

[0005] As described in Patent Document 1, when a resinate is contained in a magnetic paste and metal magnetic particles coated with oxide films are bound to each other via a binding part derived from the resinate, the resinate is not uniformly arranged on the oxide films, resulting in insufficient binding between the metal magnetic particles, which causes a problem that the filling rate of the metal magnetic particles decreases. This may cause a decrease in the magnetic properties (e.g., magnetic permeability) and insulation properties of the inductor.

[0006] This disclosure has been made in view of the above issues. Specifically, the primary object of this disclosure is to provide an inductor with improved magnetic properties and insulating properties, and a method for manufacturing an inductor.

[0007] The inductor of the present disclosure comprises a base body coated with an oxide film and comprising a plurality of metallic magnetic particles containing Fe and Si elements, wherein adjacent metallic magnetic particles are directly bonded to each other by the oxide films, and a coil embedded in the base body, wherein the oxide film comprises an inner oxide film in contact with the surface of the metallic magnetic particles and mainly composed of Si elements, and an outer oxide film containing an easily oxidizable metal element that is more easily oxidized than Fe elements, and the content ratio of the easily oxidizable metal element to the Fe element in the outer oxide film is 0.9 atom% or more.

[0008] The method for manufacturing an inductor according to the present disclosure is the method for manufacturing an inductor as described above, comprising: a surface treatment step of surface-treating metallic magnetic particles with a coupling agent; a metallic magnetic material formation step of forming a metallic magnetic material using the metallic magnetic particles surface-treated with the coupling agent; and a heat treatment step of increasing the density of the metallic magnetic material by applying pressure and heat-treating the metallic magnetic material, wherein the heat treatment step is performed by supplying 2 vol% to 21 vol% of oxygen in an atmosphere, and the ratio of the thickness of the inner oxide film to the thickness of the outer oxide film is 0.22 to 0.91.

[0009] According to this disclosure, it is possible to provide an inductor with improved magnetic properties and insulating properties, as well as a method for manufacturing an inductor.

[0010] Figure 1 is a perspective view of the inductor of this disclosure. Figure 2 is an exploded perspective view of the inductor of this disclosure. Figure 3 is a cross-sectional view of the metallic magnetic particles used in the inductor of this disclosure. Figure 4 is a graph showing the results of EDX quantitative analysis of the metallic magnetic particles shown in Figure 3. Figure 5 is a graph showing the relationship between the degree of IR degradation and the ratio of easily oxidized metal elements to Fe elements. Figure 6 is a graph showing the relationship between the saturation magnetic flux density and the ratio of easily oxidized metal elements to Fe elements. Figure 7 is a graph showing the relationship between the degree of IR degradation and the thickness of the oxide film. Figure 8 is a graph showing the IR reduction rate. Figure 9 is a graph showing the permeability.

[0011] The inductor described herein will be explained in detail below. While the explanation will be given with reference to the drawings as necessary, the illustrations are provided for illustrative purposes only to help understand this disclosure, and the appearance and dimensional ratios may differ from those of the actual product.

[0012] <Description of the Inductor of the Disclosure> The inductor of the Disclosure will be described with reference to Figures 1 and 2. The inductor of the Disclosure comprises a base body 10 which is formed by laminating a magnetic layer ML containing a plurality of metallic magnetic particles and a coil conductor CD.

[0013] The base body 10 is, for example, a rectangular prism shape or a roughly rectangular prism shape having six faces. The corners and edges of the base body 10 may be rounded. The corners are the parts where three faces of the base body 10 intersect, and the edges are the parts where two faces of the base body 10 intersect.

[0014] In Figure 1, the length, width, and height directions of the inductor 1 and the base body 10 are shown as the L direction, W direction, and T direction, respectively. The length direction L, the width direction W, and the height direction T are orthogonal to each other. The mounting surface of the inductor 1 is, for example, a surface parallel to the length direction L and the width direction W (LW surface).

[0015] The base body 10 shown in Figure 1 has a first main surface 11 and a second main surface 12 facing the height direction T, a first end surface 13 and a second end surface 14 perpendicular to the height direction T and facing the length direction L, and a first side surface 15 and a second side surface 16 perpendicular to the width direction W, which is perpendicular to both the length direction L and the height direction T. In the example shown in Figure 1, the first main surface 11 of the base body 10 corresponds to the mounting surface (bottom surface) of the base body 10. The second main surface 12 may also be the mounting surface of the base body 10.

[0016] The base body 10 has a laminated structure in which multiple layers, each having a magnetic layer ML and a coil conductor CD, are stacked in the stacking direction (for example, the height direction T). In this embodiment, the base body 10 is constructed by stacking layers G1 to G8 as shown in Figure 2. A coil is constructed by stacking multiple coil conductors CD. Constructing a coil by stacking coil conductors CD contributes to miniaturization. Note that the boundaries between each layer of the laminated structure of the base body 10 are lost. Furthermore, each layer G1 to G8 may be constructed by stacking multiple identical patterns.

[0017] The main body 10 contains a coil formed by stacking multiple coil conductors CD. In the example shown in Figure 2, two coils (a first coil and a second coil) are provided within the main body 10 along the stacking direction. More specifically, the first coil is formed by the coil conductors CD of layers G4 and G5, and the second coil is formed by the coil conductors CD of layers G2 and G3. The coil conductors CD mainly consist of Ag. Using Ag can improve the inductance characteristics. As an example of the material for the coil conductors CD, metal conductors such as Cu, Au, or their alloys may be used instead of Ag. Furthermore, the inductor 1 of the first embodiment is not limited to this example, and for example, three or more coils may be provided along the stacking direction. In addition, a coil array may be formed by arranging multiple coils side by side in a direction intersecting the stacking direction (direction L in Figure 1) inside the main body 10.

[0018] External electrodes E are provided on the mounting surface (first main surface 11) of the base body 10. In the example shown in Figure 2, the external electrodes E include a first external electrode E1 and a second external electrode E2 connected to each end of the first coil, and a third external electrode E3 and a fourth external electrode E4 connected to each end of the second coil. Note that two external electrodes are provided for each coil. Therefore, if the number of coils is three, the number of external electrodes may be six.

[0019] A through-hole conductor TH may be used to connect the coil to the external electrode E. That is, the first through-hole conductor TH1 to the fourth through-hole conductor TH4 may be provided corresponding to the first external electrode E1 to the fourth external electrode E4. Furthermore, the first through-hole conductor TH1 to the fourth through-hole conductor TH4 may extend along the lamination direction.

[0020] As described above, if the base body 10 has a laminated structure comprising layers G1 to G8, the design freedom of the inductor is increased. For example, when manufacturing an inductor having first external electrodes E1 to fourth external electrodes E4 on the bottom surface (first main surface 11) of the base body 10, it becomes easier to draw out the coils (first coil and second coil) to the bottom surface side using through-hole conductors. The laminated structure comprising layers G1 to G7 may be laminated from the second main surface 12 side or the first main surface 11 side of the base body 10. Furthermore, the material constituting the through-hole conductor TH and / or via conductor may be repeatedly printed sequentially by screen printing or the like until the desired thickness of the via conductor is achieved, or it may be formed by sputtering, inkjet printing, or other known methods.

[0021] Here, we will describe in detail, with reference to Figure 3, the metallic magnetic particle MP, which is one of the characteristic components of the inductor of this disclosure.

[0022] The metallic magnetic particles MP may contain the elements Fe (iron) and Si (silicon). More specifically, they may be Fe alloy particles. Examples of Fe alloys include Fe-Si alloys, Fe-Si-Cr (chromium) alloys, Fe-Si-Al (aluminum) alloys, Fe-Si-B (boron)-P (phosphorus)-Cu (copper)-C (carbon) alloys, Fe-Si-B (niobium)-Cu alloys, etc.

[0023] The surface of the aforementioned metal magnetic particles MP is coated with an oxide film OL. Adjacent metal magnetic particles MP are directly bonded to each other by the oxide films. In this specification, "directly bonded to each other by the oxide films" means that the oxide films are in direct contact with each other without the use of other components. In other words, the metal magnetic particles MP of this disclosure are bonded by direct contact between the oxide films, without using the bonding portion described in Patent Document 1, which is disclosed as prior art. Furthermore, by covering the surface of the metal magnetic particles with the oxide film OL, insulating properties can be provided to the metal magnetic particles MP.

[0024] More specifically, regarding the surface of the metallic magnetic particle MP, as shown in Figure 3, an example, the oxide film OL comprises an inner oxide film OLi and an outer oxide film OLo positioned outside the inner oxide film OLi. In this case, the inner oxide film OLi and the outer oxide film OLo may be formed by thermal oxidation through a heat treatment process after surface treatment of the metallic magnetic particle with a coupling agent, as will be described in detail later in the manufacturing method.

[0025] The inner oxide film OLi is in contact with the surface of the metallic magnetic particles MP and is mainly composed of Si. In this specification, "main component" refers to the element with the highest content among the metallic or metalloid elements constituting the oxide film. The inner oxide film OLi may be determined by EDX quantitative analysis (see, for example, Figure 4) as described later.

[0026] The outer oxide film OLo may be positioned outside the inner oxide film OLi. The outer oxide film OLo contains an easily oxidizable metal element that is more readily oxidized than Fe. More specifically, easily oxidizable metal elements include Cr, Ti, Al, Zr, or Mg, or combinations thereof. In this embodiment, an example of a configuration containing the element Al will be described.

[0027] One of the characteristic features of the inductor of this disclosure is that the content ratio of easily oxidizable metal elements (for example, Al) and Fe in the outer oxide film OLo is 0.9 atom% or more.

[0028] One method for quantitatively analyzing the oxide film (inner oxide film OLi and outer oxide film OLo) is the EDX quantitative analysis method shown in Figure 4. The EDX quantitative analysis is performed as follows: (1) A sample cross-section is obtained by cutting the sample perpendicular to the mounting surface and end face of the sample, passing through the center of the sample body and the winding axis of the coil. The sample cross-section may be made flat by ion milling or the like. (2) In the obtained cross-section, the location of the metallic magnetic particles MP is identified by taking an image with a transmission electron microscope (TEM) (at a magnification of approximately 800,000 times) so that the metallic magnetic particles MP are in the field of view at the winding axis of the coil. At this identified location, compositional analysis is performed using EDX (Noran, system 7) along the arrow in the illustrated example (Figure 3, etc.), straddling the outer edge of the metallic magnetic particles MP, and a graph shown in Figure 4 is created by reflecting the amount of each composition measured by EDX at each position in the TEM. In the graph shown in Figure 4, the vertical axis represents the content percentage (atom%) of O, Si, Fe, and easily oxidizable metal elements (Al), and the horizontal axis corresponds to the measurement position in the line analysis. Also, in the graph in Figure 4, the sum of all constituent elements is set to 100%. (3) Based on the graph in Figure 4, the content percentage (atom%) of easily oxidizable metal elements (Al) / content percentage (atom%) of Fe is calculated at the position where the Fe content of the outer oxide film OLo is maximum.

[0029] Here, the boundary between the inner oxide film OLi and the metallic magnetic particles MP is determined by the Si element content ratio in the EDX quantitative analysis results. Specifically, the boundary position between the inner oxide film OLi and the metallic magnetic particles MP may be determined based on the position where the Si element content ratio exceeds the Fe element content ratio. Similarly, the boundary between the inner oxide film OLi and the outer oxide film OLo is also determined by the Si element and Fe element content ratio in the EDX quantitative analysis results. Specifically, the boundary position between the inner oxide film OLi and the outer oxide film OLo may be determined based on the position where the Si element content ratio falls below the Fe element content ratio. Furthermore, the outer surface of the outer oxide film OLo may be determined at the position where the Fe element content in the outer oxide film OLo is 40% of the maximum value.

[0030] Thus, when the content ratio of easily oxidizable metal elements (Al) and Fe in the outer oxide film OLo is 0.9 atom% or more, oxidation of Al is more likely than oxidation of Fe in the outer oxide film OLo. ２ O ３ The amount of precipitate is reduced, and the deterioration of insulation resistance (IR) can be reduced.

[0031] Furthermore, the content ratio of easily oxidizable metal elements (Al) and Fe in the outer oxide film OLo may be 15 atom% or less. The basis for this numerical range is the measurement results of the degree of IR degradation shown in Figure 5 and the content ratio of easily oxidizable metal elements (atom%) / Fe element (atom%). The "degree of IR degradation" as described herein is an index that represents the degree of deterioration of insulation resistance, expressed as the ratio of the insulation resistance of the oxide film at room temperature to the insulation resistance of the oxide film after heating to about 300°C. A higher degree of IR degradation indicates that IR degradation is occurring. According to these measurement results, it can be understood that the degree of IR degradation is reduced when the content ratio of easily oxidizable metal elements (atom%) / Fe element (atom%) is 0.9 atom% or more, and that the degree of IR degradation saturates at about 15 atom%.

[0032] Furthermore, in the metal magnetic particles MP located inside the inner oxide film OLi, the content ratio of easily oxidizable metal elements to Fe elements may be 0.1 atom% or less. In other words, the metal magnetic particles MP may contain easily oxidizable metal elements (Al elements) at an unavoidable impurity level. The basis for this numerical range is the measurement results of the saturation magnetic flux density (Bs) and the content ratio of easily oxidizable metal elements (atom%) / Fe element (atom%) shown in Figure 6. According to the results shown in Figure 6, in the metal magnetic particles MP located inside the inner oxide film OLi, when the content ratio of easily oxidizable metal elements / Fe element exceeds 0.1 atom%, a decrease in saturation magnetic flux density begins to be observed. Therefore, considering the saturation magnetic flux density, it is preferable that the ratio of easily oxidizable metal elements to Fe elements in the metal magnetic particles MP located inside the inner oxide film OLi is 0.1 atom% or less. Furthermore, even if the content ratio of easily oxidizable metal elements to Fe is 0.1 atom% or more, as mentioned above, if the content ratio of easily oxidizable metal elements to Fe in the outer oxide film is 0.9 atom% or more, the inductor will have improved magnetic and insulating properties compared to before.

[0033] The thickness of the inner oxide film OLi and the outer oxide film OLo is preferably 1 nm to 50 nm, more preferably 1 nm to 30 nm, and even more preferably 1 nm to 20 nm. For example, the location of the metallic magnetic particles MP is identified by photographing a cross-section obtained by polishing an inductor sample with a scanning electron microscope (SEM). At this identified location, compositional analysis is performed using EDX (Noran, system 7) so as to straddle the outer edge of the metallic magnetic particles MP, and by reflecting the respective composition amounts in EDX at each location in TEM, the boundary between the metallic magnetic particles MP and the inner oxide film OLi and the boundary between the inner oxide film OLi and the outer oxide film OLo can be determined as described above, thereby measuring the thickness of the inner oxide film OLi and the outer oxide film OLo covering the surface of the metallic magnetic particles MP.

[0034] A suitable relationship between the thickness of the inner oxide film OLi and the outer oxide film OLo is that the ratio of the thickness of the inner oxide film OLi to the thickness of the outer oxide film OLo may be 0.22 or more and 0.91 or less. The basis for this numerical range is the relationship between the degree of IR degradation and the thickness of the inner oxide film / the thickness of the outer oxide film, as shown in Figure 7. With such a relationship between the thickness of the inner oxide film OLi and the outer oxide film OLo, it is possible to suitably achieve a lower degree of IR degradation than that of the comparative example in which surface treatment with the coupling agent described in the [Examples] below is not performed (the degree of IR degradation of Comparative Example 1 shown in Figure 8 is 2.5).

[0035] The elements constituting the inner oxide film OLi may have decreasing elemental ratios in the order of Si, Fe, and easily oxidizable metal elements. These elemental ratios can be determined from the EDX quantitative analysis results shown in Figure 4. If the inner oxide film OLi is composed of such elemental ratios, then SiO will form the oxide film. ２ This configuration allows for good insulation characteristics to be obtained.

[0036] The elements constituting the outer oxide film OLo may have decreasing elemental ratios in the order of Fe, Si, and easily oxidizable metal elements. These elemental ratios can be determined from the EDX quantitative analysis results shown in Figure 4. With an outer oxide film OLo composed of such elemental ratios, the oxide film contains metals that are more easily oxidized than Fe, thus reducing the oxidation of Fe and allowing for the acquisition of good magnetic properties (permeability).

[0037] Furthermore, to differentiate it from the prior art described in Patent Document 1 above, the oxide film (inner oxide film OLi and outer oxide film OLo) substantially does not contain element C. This is due to the volatilization of organic components during the heat treatment process in the inductor manufacturing method described later. Therefore, the inductor according to this disclosure can have its magnetic properties further improved.

[0038] <Method for Manufacturing the Inductor of the Present Disclosure> Next, the method for manufacturing the inductor of the present disclosure will be described. The method for manufacturing the inductor of the present disclosure comprises a preparation step including a surface treatment step, a metal magnetic material formation step, and a heat treatment step. As will be described later, a degreasing step may be optionally added.

[0039] - Preparation process including surface treatment process - Prepare the magnetic material (magnetic paste) that constitutes the magnetic layers ML of layers G1 to G8 as described in Figure 2, and the conductive paste that constitutes the coil conductor CD (and through-hole conductor TH).

[0040] As an example of a method for producing a magnetic paste, a metallic magnetic powder containing Fe and Si with a D50 (cumulative 50% particle size by volume) of 2 μm to 20 μm is prepared. The metallic magnetic powder is then surface-treated with a coupling agent containing a metal element that is more easily oxidized than Fe (easily oxidizable metal element). The coupling agent containing the easily oxidizable metal element may be a coupling agent containing any of the elements Ti, Al, Zr, or Mg. A magnetic paste is produced by kneading the metallic magnetic powder surface-treated with this coupling agent with a binder such as cellulose or polyvinyl butyral (PVB) and a solvent such as a mixture of terpineol and butyl diglycol acetate (BCA).

[0041] As a conductive paste, for example, a paste containing Cu as a conductive material is prepared. Note that the conductive material is not limited to Cu; a paste made from conductive materials such as Ag, Au, or their alloys may also be used.

[0042] -Metal Magnetic Material Formation Process- Using the magnetic paste and conductive paste described above, layers G1 to G8 shown in Figure 2 are prepared and laminated by screen printing or the like.

[0043] - Heat Treatment Step - After laminating layers G1 to G8, layers G1 to G8 are pressed. Said pressing may be performed at a pressure of 300 MPa or higher. Through the pressing of layers G1 to G8, two or more metal magnetic particles MP are bonded to form a metal magnetic body. Then, heat treatment is performed on the metal magnetic body. The heat treatment temperature is a temperature at which the coil conductor is sintered, and for example, may be approximately 400°C or higher and 1000°C or lower; furthermore, to achieve both reduction in coercivity and suppression of thermal diffusion of coil conductor material components into the element body, the temperature is desirably 650°C or higher and 900°C or lower. In the heat treatment step, oxygen of 2 vol% or more and 21 vol% or less may be supplied into the atmosphere. Through heat treatment in such an atmosphere, the ratio of the thickness of the inner oxide film to the thickness of the outer oxide film can be set to 0.22 or more and 0.91 or less, and through this heat treatment, an oxide film is formed on the surfaces of the metal magnetic particles in the element body, and adjacent metal magnetic particles can be bonded to each other via the oxide film.

[0044] Here, before heat-treating the metal magnetic body, a degreasing step of removing binders contained in the magnetic paste and the conductive paste may be performed. In the degreasing step, for example, degreasing is performed at a temperature of approximately 300°C or higher and 500°C or lower. This allows the binders contained in the magnetic paste and the conductive paste to be removed.

[0045] Furthermore, in order to increase the strength of the metal magnetic body, resin may be impregnated into gaps between oxide films of adjacent metal magnetic particles and then cured. An epoxy resin is used as the impregnating resin, but one or more resins selected from the group consisting of phenolic resins, polyester resins, polyimide resins, polyolefin resins, silicone resins, acrylic resins, polyvinyl butyral resins, cellulose resins, alkyd resins, and the like may also be used. Through the above steps, the element body of the inductor of the present disclosure is formed.

[0046] Thereafter, external electrodes electrically connected to the coil conductors are formed on the formed element body. The external electrodes are formed by electrolytic plating at positions where the through-hole conductors are exposed on the mounting surface (first main surface 11) of the element body 10. The plating material may be Cu plating. Other examples include, but are not limited to, Ni-Sn, Ni-Au, Ni-Cu and / or Cu-Ni-Au. After forming the external electrodes, element singulation cutting is performed to manufacture the inductor of the present embodiment.

[0047] A detailed description of verification tests for the inductor of the present disclosure will be given below with reference to tables showing the verification test results in FIG. 8 and FIG. 9. Specifically, inductors described in the following examples and comparative examples were manufactured.

[0048] -Inductor of Example- As described in the above-mentioned method for manufacturing an inductor, the inductor of the example was manufactured through a preparation step including a surface treatment step, a metal magnetic material forming step, and a heat treatment step, to obtain an inductor having the EDX quantitative analysis results shown in FIG. 4. In other words, an inductor was manufactured in which, as an oxide film coating metal magnetic particles, the inductor comprises: an inner oxide film OL_i that is in contact with the surface of the metal magnetic particles MP and contains Si element as a main component; and an outer oxide film OL_o that contains an easily oxidizable metal element (Al element); and the content ratio of Al element to Fe element in the outer oxide film is 0.9 atom% or more.

[0049] -Inductor of Comparative Example- In the inductor of the comparative example, in the above-mentioned method for manufacturing an inductor, surface treatment with a coupling agent containing an easily oxidizable metal element is not performed. In other words, although the oxide film coating the metal magnetic particles has a two-layer structure of an inner oxide film and an outer oxide film, neither oxide film contains an easily oxidizable metal element.

[0050] <Verification Test 1> Resistance Reduction Rate (IR) Evaluation The resistance reduction rate was evaluated for the inductors of the example and comparative example. As described above, the resistance reduction rate was evaluated by the ratio of the insulation resistance of the oxide film at room temperature to the insulation resistance of the oxide film after heating to about 300°C, to assess the degree of deterioration in insulation resistance. The evaluation results are shown in Figure 8. A higher degree of IR deterioration indicates that IR deterioration has occurred. According to the evaluation results shown in Figure 8, the inductor of the example had a lower resistance reduction rate than the inductor of the comparative example, and good insulation characteristics were obtained.

[0051] <Verification Test 2> Permeability Evaluation The permeability of the inductors of the example and comparative example was evaluated. In the comparative example inductor, oxidation of the Fe element occurred because the oxide film did not contain easily oxidizable metal elements, resulting in a relatively low permeability. On the other hand, in the example inductor, the oxidation of the Fe element was reduced because the oxide film contained easily oxidizable metal elements, resulting in a good permeability.

[0052] As described above, the inductor and the method for manufacturing the inductor according to this disclosure can further improve magnetic properties and insulating properties.

[0053] The embodiments disclosed herein are illustrative in all respects and do not constitute a limiting interpretation. Therefore, the technical scope of this disclosure is not construed solely by the embodiments described above, but is defined based on the claims. Furthermore, the technical scope of this disclosure includes all modifications within the meaning and scope of equivalence to the claims. For example, while the embodiments show a case where the oxide film consists of two layers, it may consist of three or more layers. In that case, one or more layers may be formed between the inner oxide film and the outer oxide film.

[0054] The inductor of this disclosure can be used as an electronic component with low DC resistance while reducing excessive oxidation near the interface between the conductor layer and the magnetic layer.

[0055] 1 Inductor 10 Base body 11 First main surface 12 Second main surface 13 First end surface 14 Second end surface 15 First side surface 16 Second side surface G1-G8 Layers MP Metal magnetic particles ML Magnetic layer CD Coil conductor OL Oxide film OLi Inner oxide film OLo Outer oxide film E External electrodes E1-E4 First external electrodes to fourth external electrodes TH1-TH4 First through-hole conductor to fourth through-hole conductor

Claims

1. An inductor comprising: a substrate coated with an oxide film and comprising a plurality of metallic magnetic particles containing Fe and Si elements, wherein adjacent metallic magnetic particles are directly bonded to each other by the oxide films; and a coil embedded in the substrate, wherein the oxide film comprises: an inner oxide film in contact with the surface of the metallic magnetic particles and mainly composed of Si elements; and an outer oxide film containing easily oxidizable metal elements that are more easily oxidized than Fe elements, and the content ratio of the easily oxidizable metal elements to Fe elements in the outer oxide film is 0.9 atom% or more.

2. The inductor according to claim 1, wherein the easily oxidizable metal element contains any of the elements Cr, Ti, Al, Zr, or Mg.

3. The inductor according to claim 1 or 2, wherein the content ratio of the easily oxidizable metal element and the Fe element in the outer oxide film is 15 atom% or less.

4. The inductor according to any one of claims 1 to 3, wherein in the metal magnetic particles located inside the inner oxide film, the content ratio of the easily oxidizable metal element to the Fe element is 0.1 atom% or less.

5. The inductor according to any one of claims 1 to 4, wherein the ratio of the thickness of the inner oxide film to the thickness of the outer oxide film is 0.22 or more and 0.91 or less.

6. The inductor according to any one of claims 1 to 5, wherein the oxide film substantially does not contain element C.

7. The inductor according to any one of claims 1 to 6, wherein the inner oxide film has decreasing elemental ratios in the order of Si element, Fe element, and the easily oxidizable metal element.

8. The inductor according to any one of claims 1 to 7, wherein the elemental ratio of the outer oxide film decreases in the order of Fe element, Si element, and the easily oxidizable metal element.

9. A method for manufacturing an inductor according to any one of claims 1 to 8, comprising: a surface treatment step of surface-treating the metallic magnetic particles with a coupling agent; a metallic magnetic material formation step of forming a metallic magnetic material using the metallic magnetic particles surface-treated with the coupling agent; and a heat treatment step of applying pressure to increase the density of the metallic magnetic material and heat-treating the metallic magnetic material, wherein the heat treatment step involves supplying 2 vol% to 21 vol% of oxygen in an atmosphere, and the ratio of the thickness of the inner oxide film to the thickness of the outer oxide film is 0.22 to 0.91.

Images