Patent Publication Number: US-2016225512-A1

Title: Power inductor

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims benefit of priority to Korean Patent Application No. 10-2015-0014419 filed on Jan. 29, 2015, with the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a power inductor. 
     BACKGROUND 
     An inductor, an important passive element configuring an electronic circuit, together with a resistor and a capacitor, is commonly used as a component removing noise or forming an LC circuit. 
     The inductor may be classified as a wire-wound inductor, a multilayer inductor, a thin film inductor, or the like, depending on a structure thereof, and has generally been manufactured by stacking, compressing, and sintering a plurality of insulating layers on which coils are formed by printing conductive patterns. 
     Recently, in information technology (IT) products such as smartphones, and the like, power consumption has increased, and available space for the mounting of passive elements has been reduced. Therefore, demand for miniaturization and high current in direct current (DC)-bias of electronic components required to be mounted in an electronic device has increased. 
     In order to satisfy the demand for miniaturization and high current, it is advantageous to increase initial saturation magnetization of a magnetic material. Therefore, research into a power inductor using magnetic metal powder having high saturation magnetization has been actively undertaken. 
     SUMMARY 
     An aspect of the present disclosure may provide a power inductor satisfying both miniaturization and high current characteristics. 
     According to an aspect of the present disclosure, a power inductor having a structure capable of overcoming limitations of existing magnetic metal powder that may not satisfy requirements for use in an inductor, in consideration of high current and miniaturization, may be provided. 
     To this end, a power inductor includes a metal thin plate bonding structure including a plurality of metal thin plates as a magnetic material for cover parts enclosing a coil. 
     Here, the plurality of metal thin plates of the metal thin plate bonding structure may be arranged in a direction parallel with respect to a direction of a magnetic field generated by the coil. 
     In addition, the plurality of metal thin plates may have a rectangular shape or a lattice shape. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The above and other aspects, features and advantages of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a perspective view of a power inductor according to an exemplary embodiment in the present disclosure; 
         FIG. 2  is a cross-sectional view taken along line I-I′ of  FIG. 1 ; 
         FIG. 3  is an exploded perspective view of coils and a coil support layer of  FIG. 2 ; 
         FIG. 4  is a perspective view illustrating another example of the coil support layer of  FIG. 2 ; 
         FIG. 5  is a perspective view of an example of a cover part of  FIG. 1 ; 
         FIG. 6  is a perspective view of another example of a cover part of  FIG. 1 ; 
         FIG. 7  is a perspective view of another example of the cover part of  FIG. 1 ; 
         FIG. 8  is a cross-sectional view of a power inductor according to another exemplary embodiment in the present disclosure; 
         FIG. 9  is an exploded perspective view of coils and a coil support layer of  FIG. 8 ; 
         FIG. 10  is a perspective view illustrating another example of the coil support layer of  FIG. 8 ; 
         FIG. 11  is a cross-sectional view of a power inductor in which the cover part of  FIG. 7  is used; and 
         FIG. 12  is a view illustrating a direction of a magnetic field formed in the cover part when a current is applied to the power inductor of  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. 
     The disclosure may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. 
     In the drawings, the shapes and dimensions of elements may be exaggerated for clarity, and the same reference numerals will be used throughout to designate the same or like elements. 
     Hereinafter, a power inductor according to exemplary embodiments in the present disclosure will be described with reference to  FIGS. 1 through 12 . 
       FIG. 1  is a perspective view of a power inductor according to an exemplary embodiment,  FIG. 2  is a cross-sectional view taken along line I-I′ of  FIG. 1 ,  FIG. 3  is an exploded perspective view of coils and a coil support layer of  FIG. 2 ,  FIG. 4  is a perspective view illustrating another example of the coil support layer of  FIG. 2 ,  FIG. 5  is a perspective view of an example of a cover part of  FIG. 1 ,  FIG. 6  is a perspective view of another example of the cover part of  FIG. 1 , and  FIG. 7  is a perspective view of another example of the cover part of  FIG. 1 . 
     As illustrated in  FIGS. 1 and 2 , a power inductor  100  according to the present exemplary embodiment may mainly include a body  110  including a coil  130  and a cover part  150  covering the coil  130  and external electrodes  160  formed on both end surfaces of the body  110 . 
     In detail, the body  110  may have a rectangular parallelepiped shape, and may include a coil support layer  120 , the coil  130  being formed on both surfaces of the coil support layer  120 , a sealing part  140  embedding the coil  130  therein, and the cover parts  150  provided as outermost layers of the body  110 . 
     Among the components of the body  110 , the coil  130 , conductor patterns by which a current is conducted to generate a magnetic field when power is applied thereto, may be wound one or more times in spiral form on both surfaces of the coil support layer  120 , as illustrated in  FIG. 3 . 
     As illustrated in  FIG. 3 , the coil  130  may include a first coil  132  formed on one surface of the coil support layer  120  and a second coil  134  formed on the other surface of the coil support layer  120  opposite to one surface of the coil support layer  120 . 
     Here, one end of the first coil  132  may be led out to one end portion of the coil support layer  120 , and one end of the second coil  134  may be led out to the other end portion of the coil support layer  120  opposite to one end portion of the coil support layer  120 . 
     In addition, the other ends of the first and second coils  132  and  134  may be positioned to correspond to each other to thereby be electrically connected to each other by a via (not illustrated) formed in the coil support layer  120 . Here, the via may be formed by filling a via hole  124  penetrating through the coil support layer  120  in a thickness direction with a conductive material. 
     Therefore, the first and second coils  132  and  134  stacked on and below the coil support layer, respectively, may be electrically connected to each other by the via. 
     The first and second coils  132  and  134  and the via configuring the coil  130  may be formed of a material having excellent electrical conductivity, for example, at least one selected from the group consisting of gold (Au), silver (Ag), platinum (Pt), copper (Cu), nickel (Ni), palladium (Pd), aluminum (Al), titanium (Ti), and alloys thereof. However, materials of the first and second coils  132  and  134  and the via are not limited as long as they are general conductive materials. 
     The first and second coils  132  and  134  may be formed as plating layers on one surface and the other surface of the coil support layer  120 , respectively, by plating, advantageous in terms of slimness of the power inductor  100 . 
     The via may be formed by punching or drilling a region of the coil support layer  120  in which the via is to be formed in the thickness direction of the coil support layer  120  to form the via hole  124  and filling the via hole  124  with a conductive material. For example, the via may be formed of a plating layer on which a conductive material is formed by plating or may be formed of a conductive film by filling a through hole with a conductive paste and firing the same. 
     The coil support layer  120  may be formed of a planar printed circuit board (PCB). However, a material of the coil support layer  120  is not limited thereto, but may be a material commonly known in the art. 
     As illustrated in  FIGS. 3 and 4 , the coil support layer  120  may include a through-hole  122  formed in a central portion thereof, disposed in the center of the coil  130  and the via (not illustrated) formed in the via hole  124  corresponding to the other ends of the first and second coils  132  and  134 . Referring to  FIG. 4 , the coil support layer  120  may have chamfers  126  formed at corner portions thereof, and may secure a magnetic path by the through-hole  122  and the chamfers  126 . 
     Meanwhile, although the chamfers  126  are formed in all corners of the coil support layer  120  as illustrated in  FIG. 4 , the chamfer  126  may be formed at one or more corner portions. Alternatively, the chamfers  126  may be omitted as illustrated in  FIG. 3 . 
     As illustrated in  FIG. 2 , the coil  130  may be embedded by the sealing part  140  provided in the body  110 . The sealing part  140  may include an insulating layer  142  and a magnetic composite layer  144 . 
     The insulating layers  142  may enclose surfaces of the first and second coils  132  and  134  so as to prevent short-circuits occurring between conducting wires in each of the first and second coils  132  and  134  and to insulate the first and second coils  132  and  134  and the cover parts  150  from each other. 
     The insulating layer  142  may be formed of a material having insulating properties, for example, a polymer, or the like. However, a material of the insulating layer  142  is not limited thereto. 
     The magnetic composite layer  144  may be formed in an empty space between the cover parts  150  formed in upper and lower portions of the body  110 , and may enclose the entirety, or portions of, the coil  130  as well as at least a region corresponding to the through-hole  122  (see  FIG. 3 ) of the coil support layer  120 .  FIG. 2  illustrates that the magnetic composite layer  144  is formed to have a height matching that of the coil  130  coated with the insulating layer  142  to enclose portions of the coil  130 . 
     The magnetic composite layer  144  may be formed of a composite material of a magnetic metal powder  144   a  and a binder  144   b , and may contain spherical magnetic metal powder particles in order to have a high packing factor. 
     The magnetic metal powder  144   a  may be formed of a magnetic material, for example, at least one selected from the group consisting of iron (Fe), an iron-nickel (Fe—Ni)-based alloy, an iron-silicon (Fe—Si)-based alloy, an iron-silicon-aluminum (Fe—Si—Al)-based alloy, an iron-chromium-silicon (Fe—Cr—Si)-based alloy, an iron (Fe)-based amorphous alloy, an iron (Fe)-based nanocrystalline alloy, a cobalt (Co)-based amorphous alloy, an iron-cobalt (Fe—Co)-based alloy, an iron-nitrogen (Fe—N)-based alloy, manganese-zinc (Mn—Zn)-based ferrite, and nickel-zinc (Ni—Zn)-based ferrite. 
     Since the magnetic composite layer  144  containing the magnetic metal powder particles  144   a  as described above has a high magnetic flux density, the magnetic composite layer  144  may apply a large bias magnetic field to contribute to a high output current of a direct current (DC) to DC converter and generate a significant effect. 
     In addition, the magnetic composite layer  144  may be formed of a mixture of two or more kinds of magnetic metal powder  144   a  including coarse particles and fine particles having different average particle sizes. This may allow for an increase in the density of the magnetic metal powder  144   a  in the magnetic composite layer  144  to increase magnetic permeability. 
     In this case, as the difference in size between the coarse particles and the fine particles of the magnetic metal powder  144   a  is increased, the magnetic permeability is improved. However, it may be more advantageous in terms of improvement of the magnetic permeability when an average particle size of the fine particles of the magnetic metal powder  144   a  is 1.0 μm or more. The reason is that when a surface area of the magnetic metal powder  144   a  after being bonded to each other is excessively increased due to a decrease in the size of the magnetic metal powder particles, a packing density of the magnetic metal powder particles  144   a  may not be increased due to the binder  144   b  bonding the magnetic metal powder particles  144   a  to each other. 
     Meanwhile, a material of the binder  144   b  may be a polymer, such as an epoxy resin, but is not limited thereto. 
     The magnetic composite layer  144  may be formed by preparing a magnetic paste in which two or more kinds of spherical magnetic metal powder particles  144   a  having different average particle sizes and the binder  144   b  such as the epoxy resin, are contained in an organic solvent, applying the magnetic paste to enclose the entirety or portions of the coil  130  as well as the region corresponding to the through-hole  122  (see  FIG. 3 ) of the coil support layer  120 , and then hardening the applied magnetic paste. 
     As illustrated in  FIG. 2 , the cover parts  150 , among components of the body  110 , may be formed on the sealing part  140  embedding the coil  130  therein. 
     The cover parts  150  may be positioned above and below the coil  130  to prevent deteriorations in electrical characteristics of the coil  130 . 
     In the present exemplary embodiment, the cover part  150  may be formed of a metal thin plate bonding structure including a plurality of metal thin plates  152  formed of a magnetic material and bonding members  154  bonding neighboring metal thin plates  152  to each other. 
     In general, a cover part of an inductor has been formed of a composite material of magnetic metal powder particles and a polymer. The reason is that the magnetic metal powder particles have saturation magnetization greater than that of ferrite to have a high magnetic flux density, thereby satisfying requirements for high current according to the following Equation 1: 
     
       
         
           
             
               
                 
                   L 
                   = 
                   
                     
                       N 
                        
                       
                         φ 
                         1 
                       
                     
                     = 
                     
                       
                         
                           N 
                           · 
                           A 
                           · 
                           B 
                         
                         1 
                       
                       . 
                     
                   
                 
               
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     1 
                   
                   ] 
                 
               
             
           
         
       
     
     Here, L is inductance of the inductor, B is magnetic flux density, A is an area through which a magnetic flux passes, N is the number of windings of the coil, and I is an amount of current. 
     Recently, in order to satisfy requirements for high efficiency, high DC-bias at high current, miniaturization, and the like that have been demanded in a power inductor product group, magnetic permeability of magnetic metal powder needs to be further increased. However, at present a magnetic metal material in a powder state has reached a limit in terms of increasing the magnetic permeability thereof. 
     The applicant has concluded that bulk metal needs to be used in order to improve the magnetic permeability of the magnetic metal material as a result of a test performed on various materials, material compositions, and the like. 
     Therefore, in the present disclosure, a magnetic metal material forming the cover part  150  of the power inductor  100  has been changed from an existing powder type into a thin film type divided from the bulk metal, an example and an effect of which will be described in detail below. 
     As a size of a metal material such as bulk metal is increased, eddy current loss may be increased, and thus, energy efficiency may be decreased and magnetic characteristics may be deteriorated. 
     In order to solve the above-mentioned problems, the metal thin plates  152  divided from the bulk metal were used in the cover parts  150 . In the present exemplary embodiment, a thickness of the metal thin plates  152  is equal to a distance between neighboring metal thin plates  152  in  FIG. 5 . 
     The metal thin plate  152  may be formed of at least one selected from the group consisting of a crystalline material, an amorphous material, a nanocrystalline material created in a crystalline structure having a nano size through heat treatment, and the like. 
     Here, an alloy composition of the metal thin plate  152  may be an alloy of two or more components such as iron-silicon-chromium (Fe—Si—Cr), iron-silicon (Fe—Si), iron-silicon-chromium-boron (Fe—Si—Cr—B), or iron-silicon-boron-phosphorus-copper-niobium (Fe—Si—B—P—Cu—Nb). 
     Magnetic permeability characteristics and loss characteristics of the amorphous material and the nanocrystalline material may be improved through the heat treatment of the amorphous material and the nanocrystalline material. In a case of performing the heat treatment on the amorphous material and the nanocrystalline material, the amorphous material and the nanocrystalline material may be heat-treated before an adhesive is applied to the metal thin plate  152 , and needs to be heat-treated under an inert gas atmosphere in order to prevent oxidation of a metal at the time of being heat-treated. 
     Particularly, in a case of the nanocrystalline material, it may be confirmed by X-ray diffraction (XRD) analysis that crystal peaks are created through the heat treatment of the nanocrystalline material, and it may be confirmed from an analysis such as a transmission electron microscope (TEM) analysis, that crystal grains having a size of 20 nm or less are created. 
     The amorphous material may be more advantageous in improvements of magnetic permeability as compared with the crystalline material. However, since low saturation magnetization is formed in the amorphous material due to a decrease in the content of iron (Fe) and an increase in the content of a non-magnetic component for amorphization, the crystalline material of which a content of iron (Fe) is high may have better characteristics in terms of improvements of DC-bias. Therefore, the crystalline material and the amorphous material may be mixed with each other in tuning magnetic permeability and DC-bias, thereby more flexibly coping with improvements of characteristics of a magnetic element. 
     In consideration of improvements of the DC-bias, only the crystalline material may be used as a material of the metal thin plate  152 . In this case, Fe-6.5 wt % Si alloy may be used. The Fe-6.5 wt % Si alloy may have excellent magnetostrictive characteristics to improve loss characteristics of a material. However, when the content of Si is decreased to 6.5 wt % or less, the loss characteristics may be deteriorated, which is undesirable. 
     In addition, the metal thin plate  152  may be formed to be relatively thin, for example, a thickness of 20 μm or less, in order to improve eddy current loss. 
     The metal thin plate  152  may be processed in a plate shape from a melt of at least one selected from the group consisting of the crystalline material, the amorphous material, the nanocrystalline material, and the like, having an alloy composition such as Fe—Si—Cr, Fe—Si, Fe—Si—Cr—B, or Fe—Si—B—P—Cu—Nb. 
     As illustrated in  FIG. 5 , the metal thin plate  152  may have a rectangular shape. A plurality of metal thin plates  152  having the rectangular shape described above may be bonded to each other by the bonding members  154  to form the cover part  150 , the metal thin plate bonding structure. 
     The bonding member  154  bonding neighboring metal thin plates  152  to each other may be formed of an insulating material, for example, a single organic material or a composite of an inorganic material and an organic material. Here, the organic material may be a thermosetting epoxy resin, enamel, or the like, but is not limited thereto. 
     In the cover part  150  having the structure illustrated in  FIG. 5 , as illustrated in  FIG. 2 , the plurality of metal thin plates  152  may be arranged in a length direction of the body  110 . That is, the plurality of metal thin plates  152  may be arranged perpendicularly with respect to an upper surface of the coil  130 . 
     In this case, the metal thin plates  152  may be arranged in a direction parallel with respect to a direction of a magnetic field generated by the coil  130 . 
     As illustrated in  FIG. 6 , the entire thin plate bonding structure may be formed in a lattice shape by forming one or more cut surfaces in a direction perpendicular to a length direction of the metal thin plates  152  illustrated in  FIG. 5 , in order to improve additional eddy current loss and improve a quality (Q) factor. 
     In this case, the metal thin plates  152  each having a block shape may be arranged in both a direction parallel with respect to, and a direction perpendicular with respect to, the direction of the magnetic field generated by the coil  130 . 
     Meanwhile, the bonding members  154 , insulating materials, may be filled between the cut surfaces of the metal thin plates  152  having the lattice shape. 
     Unlike the example of  FIG. 5 , as illustrated in  FIG. 7 , the plurality of metal thin plates  152  may be arranged in a width direction of the body  110 . Also, in this case, the plurality of metal thin plates  152  may be arranged perpendicularly with respect to the upper surface of the coil  130 . 
     In addition, in  FIG. 7 , the neighboring metal thin plates  152  may be bonded to each other by the bonding members  154  to form the cover part  150 , the metal thin plate bonding structure. 
     In  FIGS. 5 through 7 , it may be advantageous, in terms of increasing magnetic permeability and improving DC-bias, that the bonding members  154  are formed to be as thin as possible. Therefore, the bonding members  154  may be formed at a thickness of 5 μm or less. However, in a case in which volumes of the metal thin plates  152  are decreased in the metal thin plate bonding structure due to a design factor, forming the bonding members  154  to have a thickness of 5 μm or more may also be considered. 
     In addition, a packing factor of the metal thin plates  152  in the cover part  150  may be maintained at a level of 80% or more, preferably, 80 to 95%, in order to improve magnetic permeability and DC-bias through control of the numbers, thicknesses, and the like, of the metal thin plates  152  and the bonding members  154  in the cover part  150 . 
     Here, when the packing factor of the metal thin plates  152  is lower than 80%, the content of magnetic material may be excessively low, and thus, it may be difficult to implement high magnetic permeability and high DC-bias. On the contrary, when the content of the metal thin plates  152  exceeds 95%, adhesion may be decreased, and thus, it may be difficult to maintain a shape of the cover part. 
     A general thin film power inductor may be formed of a composite of metal powder and a hardening member such as epoxy, such that a packing factor of a metal may be 80% or more at the time of implementing a PI chip. Therefore, even when the metal thin plates are used in the exemplary embodiments, a metal volume needs to be secured so that a packing factor of a metal is 80% or more, similar to that of an existing thin film power inductor, in order to secure a characteristic improvement effect. 
     Again, referring to  FIGS. 1 and 2 , a pair of external electrodes  160  among components of the power inductor  100  may be formed on both end surfaces of the body  110 . 
     One of the pair of external electrodes  160  may be connected to the first coil  132  led out to one end portion of the coil support layer  120 , and the other of the pair of external electrodes  160  may be connected to the second coil  134  led out to the other end portion of the coil support layer  120 . That is, the external electrodes  160  may serve as external terminals electrically connecting the coil  130  and external circuits to each other. 
     The external electrodes  160  may be formed of a general conductive material, for example, a conductive material selected from the group consisting of gold (Au), silver (Ag), platinum (Pt), copper (Cu), nickel (Ni), palladium (Pd), and alloys thereof. 
     The external electrodes  160  may be formed by plating the metal to cover both end surfaces of the body  110  using a dipping method, or the like, and sintering the metal at a temperature of about 700° C. to 900° C. 
     Meanwhile,  FIG. 8  is a cross-sectional view of a power inductor according to another exemplary embodiment in the present disclosure,  FIG. 9  is an exploded perspective view of coils and a coil support layer of  FIG. 8 , and  FIG. 10  is a perspective view illustrating another example of the coil support layer of  FIG. 8 . 
     In the power inductor according to the exemplary embodiment of  FIG. 8 , components the same as the components of the power inductor according to the exemplary embodiment of  FIG. 2  described above will be denoted by the same reference numerals, while overlapped descriptions of the same components will be omitted, and only differences between the power inductor according to the exemplary embodiment of  FIG. 8  and the power inductor according to the exemplary embodiment of  FIG. 2  will be described. 
     The power inductor according to the exemplary embodiment illustrated in  FIG. 8  may be the same as the power inductor  100  according to the exemplary embodiment illustrated in  FIG. 2 , except that the through-hole is not formed in the central portion of the coil support layer  120  and a position of the magnetic composite layer  144  is changed since the through-hole is not formed. 
     As illustrated in  FIGS. 8 through 10 , in a power inductor  100 ′ according to another exemplary embodiment, the coil support layer  120  may include a via (not illustrated) formed in the via hole  124  corresponding to the other ends of the first and second coils  132  and  134  and chamfers  126  formed at corner portions thereof, and may secure a magnetic path by the chamfers  126 . 
     Here, the coil support layer  120  may not include the through-hole in the central portion thereof in order to serve as a gap for improving DC-bias. 
     Alternatively, the chamfer  126  formed in all the corners of the coil support layer  120  in  FIG. 10  may be formed in one or more corner portions thereof, and may be omitted as illustrated in  FIG. 9 . 
     As described above, in a case in which coil support layer  120  does not include the through-hole in the central portion thereof, the magnetic composite layers  144  may be disposed on and below the coil support layer  120 . 
     Meanwhile,  FIG. 11  is a cross-sectional view of a power inductor in which the cover part of  FIG. 7  is used. 
     In the power inductor according to the exemplary embodiment of  FIG. 11 , components the same as those of the power inductor according to the exemplary embodiment of  FIG. 8  described above will be denoted by the same reference numerals, while overlapped descriptions of the same components will be omitted, and only a difference between the power inductor according to the exemplary embodiment of  FIG. 11  and the power inductor according to the exemplary embodiment of  FIG. 8  will be described. 
     In a power inductor  100 ″ according to the exemplary embodiment illustrated in  FIG. 11 , the cover part  150  illustrated in  FIG. 7  may be used. Therefore, the power inductor  100 ″ according to the exemplary embodiment illustrated in  FIG. 11  may be the same as the power inductor  100 ′ according to the exemplary embodiment illustrated in  FIG. 8 , except that the thickness of the metal thin plates  152  is arranged in the width direction of the body  110 . Also, in a case in which cut surfaces are formed in the length direction of the metal thin plates  152  as described above, additional improvements in loss characteristics may be expected. 
     In addition, although not illustrated in the drawings, the coil support layer  120  may include the through-hole  122  or the chamfers  126  of  FIG. 4  as in the exemplary embodiment of  FIG. 2 . 
       FIG. 12  is a view illustrating a direction of a magnetic field formed in the cover part when a current is applied to the power inductor of  FIG. 8 . 
     Due to the above-mentioned configuration, when a current flows in the coil  130  of  FIG. 12 , the metal thin plates  152  may be positioned to be perpendicular to a direction P of a magnetic field generated by the coil  130 , such that free electrons in the metal thin plates  152  may generate a flow of a rotating current by an influence of the magnetic field, to cause eddy current loss. 
     However, in  FIG. 12 , a size of a metal may be decreased through the metal thin plates  152  to induce a decrease in eddy current loss, thereby improving loss characteristics. 
     In the power inductors  100 ,  100 ′, and  100 ″ according to the exemplary embodiments configured as described above, the magnetic metal material having the high saturation magnetization may be used, and a thin plate type bulk metal using shape anisotropy rather than a powder type material may be used to realize an increase in magnetic permeability, thereby satisfying demands for improvements in DC-bias, improvements in DC resistance (Rdc) due to a decrease in the number of turns of coil, and miniaturization of the power inductor. 
     1. Manufacturing of Sample 
     Inventive Example 
     A core manufactured by insulating nanocrystalline-based alloy metal thin plates having a thickness of 20 μm from each other by epoxy and winding copper conducting wires was heat-hardened. 
     Comparative Example 
     Core samples formed of a composite of metal powder and epoxy and having a doughnut shape were molded and manufactured by a compression mold and were then heat-hardened, and copper conducting wires coated with an insulating material were wound ten times with respect to respective core samples. 
     2. Evaluation of Physical Property 
     Magnetic permeability values (μ′) and loss values (Q=μ′/μ″) of composites according to an Inventive Example and a Comparative Example are illustrated in Table 1. Here, inductance levels of two core samples according to the Inventive Example and the Comparative Example were measured by an E4982A LCR meter to compare magnetic permeability values with each other. 
     
       
         
           
               
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                 Magnetic 
                   
                   
               
               
                   
                 Component 
                 Physical 
                 Frequency Used 
               
            
           
           
               
               
               
               
               
               
            
               
                 Division 
                 of Core 
                 Properties 
                 1 MHz 
                 2 MHz 
                 3 MHz 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 Comparative 
                 Metal Powder 
                 μ′ 
                 29.5 
                 29.3 
                 29.3 
               
               
                 Example 
                   
                 Q = μ′/μ″ 
                 46 
                 54 
                 33 
               
               
                 Inventive 
                 Metal Thin 
                 μ′ 
                 680 
                 433 
                 323 
               
               
                 Example 
                 Plate 
                 Q = μ′/μ″ 
                 1 
                 0.8 
                 0.8 
               
               
                   
               
            
           
         
       
     
     Referring to Table 1, it can be seen that significantly higher magnetic permeability is obtained in a core formed of a metal thin plate according to the Inventive Example than in a core formed of a metal powder according to the Comparative Example. 
     In addition, since the magnetic permeability of the Inventive Example is twenty times higher than that of the Comparative Example at a frequency of 1 MHz, inductance may be increased in the Inventive Example as compared to the Comparative Example at the same number of turns. Therefore, in the case of the Inventive Example, the number of turns of coil needs to be decreased in order to allow inductance to be matched to a designed inductance. Therefore, Rdc of the coil may be decreased, such that loss characteristics may also be improved. 
     As set forth above, in a power inductor according to exemplary embodiments, a thin plate type bulk metal using shape anisotropy may be used as a magnetic material of the cover part, thereby satisfying demands for high current in DC-bias, improvement in DC resistance (Rdc) due to a decrease in the number of turns of coil, and miniaturization of the power inductor. 
     While exemplary embodiments have been shown and described above, it will be apparent to those skilled in the art that modifications and variations could be made without departing from the scope of the present invention as defined by the appended claims.