Patent Publication Number: US-7212094-B2

Title: Inductive components and electronic devices using the same

Description:
THIS APPLICATION IS A U.S. NATIONAL PHASE APPLICATION OF PCT INTERNATIONAL APPLICATION PCT/JP2003/013894. 
   TECHNICAL FIELD 
   The present invention relates to inductive components for use in power supply circuits of portable telephones and the like and to electronic devices using the inductive components. 
   BACKGROUND ART 
   Referring to  FIG. 11 , a description of power supply circuits for use in portable telephones and the like will be given. 
   Using a voltage of 4V, for example, of battery  101  as the input voltage, it is possible to obtain an output voltage of 2V. Here, coil  102  is called a choke coil. By putting coil  102  in the circuit, a stable output voltage can be obtained. Also, in order to more stabilize the output voltage, it is necessary to increase the inductance of coil  102 . In this way, the power supply circuit of  FIG. 11  is capable of supplying a DC output voltage which is more stabilized. 
   Generally, in order to increase the inductance of coil  102 , it is necessary to increase the cross-sectional area of the core of coil  102  and to increase the number of turns. This presents a problem of a need to increase the volume of coil  102 . On the other hand, in association with the requirement in recent years for a smaller size and lower profile design of portable telephones, there is an increasingly stronger requirement for smaller size and lower profile design of coils for the power supply circuit of portable telephones. For example, coil  102  with an area smaller than 5 mm×5 mm and a thickness of less than 1 mm is being required. Furthermore, the switching frequency has increased from several hundred kHz to several tens of MHz. In association with such a trend toward higher frequencies of the switching frequency, reduction in the core loss is being required. Also, as devices have come to be used at lower voltages and higher currents, there is a case in which a maximum current greater than 0.1 A flows in a coil having a small size and a low profile. For this reason, it is necessary to reduce the resistance of the coil to a lower value. 
   Japanese Laid-Open Patent Application No. H09-223636 (page 3,  FIG. 1 ) discloses a method for solving these issues. 
   Referring to  FIG. 12 , a description of a conventional inductive component will be given. Multilayer magnetic films  112  support coil  111  in a manner sandwiching with the intervention of interlayer insulating layer  115 . And through-hole sections (hereinafter “THP”)  114  are provided on the sides and in the center of coil  111 . Furthermore, THP  114  is filled with magnetic material  113 . Also, as coil  111  is formed by winding a strip of high electric-conductivity materials such as copper, coil  111  can be made thin. However, the above-mentioned coil with a conventional configuration suffered a problem that the inductance could not be increased to a high enough value. Furthermore, as magnetic layer  113  is formed inside THP  114 , the cross-sectional area of magnetic layer  113  becomes large. When a current is fed through coil  111 , a magnetic flux that vertically penetrates THP  114  is generated, and an eddy current is generated in the horizontal plane of magnetic layer  113 . As the cross-sectional area of magnetic layer  113  is large, the eddy current is large. 
   As a result, the magnetic flux that vertically penetrates THP  114  is reduced. 
   Consequently, the inductance of the coil cannot be increased. On the other hand, by using a magnetic material having a higher specific resistance, the eddy current can be reduced to a certain extent. However, when the switching frequency increases from several hundred kHz to several tens of MHz, a satisfactory effect of eddy current reduction cannot be obtained. Also, when the diameter of a through hole is 1 mm or smaller, and the depth is 0.1 mm or greater and 1 mm or smaller, for example, it is difficult to fill or dispose a magnetic material into the THP by sputtering or vapor deposition because of difficulties in quality and productivity. The present invention addresses these issues and provides inductive components with which sufficient inductance is obtainable even when designed with a smaller size and a lower profile, and electronic devices that use those inductive components. 
   SUMMARY OF THE INVENTION 
   The present invention provides an inductive component including a coil, a through hole part and a multilayer magnetic layer, wherein the multilayer magnetic layer is disposed on the inner wall of the through hole part and the top and the bottom surfaces of the coil. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of an inductive component of Embodiment 1 of the present invention. 
       FIG. 2  is a cross-sectional view of an inductive component of Embodiment 1 of the present invention. 
       FIG. 3  is an enlarged cross-sectional view of THP of Embodiment 1 of the present invention. 
       FIG. 4  is an enlarged cross-sectional view of the top surface of a coil of Embodiment 1 of the present invention. 
       FIG. 5  is an enlarged cross-sectional view of the inner wall of THP of Embodiment 1 of the present invention. 
       FIG. 6  is an enlarged cross-sectional view of the inner wall of THP of Embodiment 2 of the present invention. 
       FIG. 7  is an enlarged cross-sectional view of a corner section of a multilayer magnetic layer of Embodiment 3 of the present invention. 
       FIG. 8  is an enlarged cross-sectional view of the top section of THP of Embodiment 4 of the present invention. 
       FIG. 9  is a perspective view of a multilayer magnetic layer of Embodiment 5 of the present invention. 
       FIG. 10  is an enlarged perspective view of the inner wall of THP of Embodiment 6 of the present invention. 
       FIG. 11  is a circuit diagram of a power supply circuit used in a portable telephone. 
       FIG. 12  is a cross-sectional view of a conventional inductive component. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION 
   Referring to drawings, a description of preferred embodiments of the present invention will be given in the following. The drawings are schematic diagrams and do not represent dimensionally correct positions. 
   (Embodiment 1) 
     FIG. 1  and  FIG. 2  illustrate an inductive component of Embodiment 1. In  FIG. 2 , coil  21  and through-hole electrode  50  are formed with a plated high-conductivity material such as copper and silver. Needless to say, coil  21  may be formed with a copper wire. THP  22  is formed in the center of coil  21 . Depending on the occasion, THP  22  may be formed on the outside of coil  21 . While the thickness of coil  21  differs depending on the device in which it is to be used, at least a thickness of 10 μm is necessary in order to cope with a large current. Also, the coil on the upper level of coil  21  is spirally wound toward THP  22  starting from terminal  23  located on one of the sides of the inductive component. The coil then moves to the lower level at the center and is spirally wound toward terminal  24  located at the other side of the inductive component starting from through-hole electrode  50 . Here, the directions of winding of the upper level and lower level coils of coil  21  are the same. Accordingly, when a current is fed from terminal  23 , it spirally flows from a side of the inductive component toward the center through the upper level of coil  21 . The current further flows from the upper level to the lower level, and spirally flows through the lower level of coil  21  from the center of the inductive component toward the side, and is put out from terminal  24 . Coil  21  may not necessarily be of two levels and may be of one level or three or more levels. Coil  21  is buried inside coil insulating material  25 . Coil insulating material  25  prevents coil  21  from short-circuiting. 
   Next, multilayer magnetic layer (hereinafter “MLM”)  30  is disposed on the top surface of coil  21  and the inner wall of THP  22  is formed at the same time. Here, MLM  3 O consists of magnetic layers  26  and insulating layers  29 . Furthermore, MLM  30  is also formed on the bottom surface of coil  21 . Insulating material  27  is formed in a manner covering MLM  30 . That is, it covers MLM  30  on the top and bottom surfaces of coil  21  as well as MLM  30  inside THP  22 . Insulating material  27  is also filled in the space formed by MLM  30  inside THP 22 . Insulating material  27  is provided in order to prevent short-circuit when mounting the inductive component on an electronic component in a state in which MLM  30  is exposed. 
   While  FIG. 2  illustrates a state in which the space formed by MLM  30  inside THP 22  is totally filled with insulating material  27 , it is not necessary to totally fill the space. However, when sucking and mounting the inductive component on a substrate, it is more preferable that insulating material  27  be totally filling the space formed by MLM  30  inside THP  22 . Also, as insulating material  27 , an organic resin such as epoxy resin, silicone resin, or acrylic resin is preferable. 
   In  FIG. 2 , although all of MLM  30  is formed into an integrated unit, it need not necessarily be integrated. However, in order not to produce a magnetic gap, it is preferable to form a continuous magnetic layer at corner section  71  of THP  22  where magnetic fluxes tend to concentrate most intensely. By forming the magnetic layer in this way, leakage flux can be made smaller and inductance can be made larger. By the way, a magnetic material may be disposed on MLM  30  inside THP  22 . When doing this, it is more preferable that the magnetic material be brought into as intimate contact as possible in order not to produce a magnetic gap. Also, the magnetic material is made of at least one material selected from the group consisting of a ferrite magnetic material, a composite of ferrite magnetic powder and an insulating resin, and a composite of metal magnetic powder and an insulating resin. With this configuration, superior reliability is obtainable as superior insulation can be obtained and possibility of occurrence of short-circuit in the circuit can be reduced even without insulating material  27 . 
     FIG. 3  is an enlarged cross-sectional view of THP  22 . Plating under-layer  28  is provided in order to form MLM  30  on coil insulating material  25 . That is, it is provided to facilitate formation of magnetic layer  26  on plating under-layer  28  by electroplating. Plating under-layer  28  is formed by electroless plating, for example, and copper, nickel or metal magnetic layer having good conductivity is preferably used. 
   MLM  30  is formed in a manner such that insulating layer  29  interposes magnetic layers  26  as illustrated in  FIG. 4 . MLM  30  is formed as follows. First, magnetic layer  26  is formed by electroplating on plating under-layer  28  followed by forming insulating layer  29  on top of it by electroplating or electrodeposition. Furthermore, thin MLM  30  can be formed by succeedingly forming a magnetic layer, an insulating layer, and a magnetic layer. In  FIG. 4 , MLM  30  has three layers. However, the number of the magnetic layers may be one or two, or four or more. Same thing applies to the structure of MLM  30  to be disposed under the coil. Furthermore, when forming MLM  30 , in order to facilitate formation of a magnetic layer by electroplating, an under layer similar to plating under-layer  28  may be provided between the insulating layer and the magnetic layer. The magnetic layer may be formed by electroplating. Needless to say, similar advantage is obtainable by laminating MLM  30  by a method other than what is described above so far as the structure is the same. 
   MLM  30  is formed in a manner such that the main component of at least one of the layers of MLM  30  includes at least one element selected from the group consisting of Fe, Ni, and Co. In this way, a magnetic layer having superior magnetic properties for satisfying requirement for a high saturation magnetic flux density and a high magnetic permeability to cope with a large current can be obtained, and a high inductance can be realized. Thickness of each of the magnetic layers differs depending on the switching frequency. Assuming a switching frequency range of several hundred kHz to several tens of MHz, the thickness is preferably between 1 μm to 50 μm. Also, while the thickness of each insulating layer differs depending on the specific resistance, the preferable range is from 0.01 μm to 5 μm. While the specific resistance of the insulating layer is the higher the better, the insulating layer is effective so far as the ratio of its specific resistance to that of the magnetic layer is 10 3  or higher. As the material for the insulating layer, organic resins or inorganic materials such as metal oxides are preferable. A mixture of these materials is also good. 
     FIG. 5  is an enlarged cross-sectional view of the inner wall of THP  22 . As shown in  FIG. 5 , MLM  30  is formed in a manner such that insulating layer  29  interposes between magnetic layers  26 . MLM  30  is formed as described below. First, magnetic layer  26  is formed by electroplating on top of plating under-layer  28  followed by formation of insulating layer  29  by electroplating or electrodeposition. MLM  30  is formed by further sequentially forming a magnetic layer, an insulating layer, and a magnetic layer on top of insulating layer  29 . In this way, the cross-sectional area of the magnetic layer per layer of MLM  30  is sufficiently minimized by electroplating. In  FIG. 5 , MLM  30  has three layers. However, the number of the magnetic layers may be one or two, or four or more. 
   Furthermore, in forming MLM  30 , an under layer similar to plating under-layer  28  may be provided between the insulating layer and the magnetic layer in order to facilitate the formation of magnetic layer  26  by electroplating. The magnetic layer may also be formed by electroless plating. Needless to say, when MLM  30  is formed by a method other than the above described, the same advantage is obtainable so far as the structure is the same. MLM  30  is formed in a manner such that the main component of at least one layer of MLM  30  includes at least one element selected from the group consisting of Fe, Ni, and Co. In this way, MLM  30  having superior magnetic properties for satisfying a requirement for a high saturation magnetic flux density and a high magnetic permeability to cope with a large current can be obtained. At the same time, a high inductance can be realized. Preferable thickness of each of the magnetic layers differs depending on the switching frequency. Assuming a switching frequency range of several hundred kHz to several tens of MHz, the thickness is preferably between 1 μm to 50 μm. While the thickness per layer of the insulating layers differs depending on the specific resistance, the preferable range is from 0.01 μm to 5 μm. 
   Also, while the specific resistance of the insulating layers is the higher the better, the insulating layer is effective so far as the ratio of its specific resistance to that of the magnetic layer is 10 3  or higher. As the material for the insulating layers, organic resins or inorganic materials such as metal oxides are preferable. 
   Furthermore, a mixture of these materials is also good. A description of operation of an inductive component having above configuration will now be given in the following. Coil  21  is spirally wound with high regularity and has a two-level structure with the same direction of winding. For this reason, when a current is fed to coil  21 , a strong magnetic flux is obtainable enabling an increase in the inductance of the inductive component. Accordingly, an inductive component having a large enough inductance is obtainable even when the size is made smaller and the profile is made lower. Also, coil  21  is formed by copper plating and the like and its cross-section is a square. The advantage of square cross-section of coil  21  lies in that the cross-sectional area can be made greater than that obtainable when the cross-section of coil  21  is round. As a result, coil  21  with a low electric resistance, a small size, and a low profile is obtainable. 
   By using a coil having a high space factor like this, copper loss generated in the coil can also be reduced. When a current is fed to an inductive component, a magnetic flux is generated in the inductive component. Magnetic fluxes are also generated in the direction of the plane of MLM  30  disposed on the top and the bottom surfaces of coil  21 . A magnetic flux is also generated in the direction of the plane of MLM  30  formed on the inner wall of THP  22 . Because of these fluxes, an eddy current is generated in the direction of the thickness of MLM  30 . As this eddy current reduces the magnetic flux generated in the direction of the plane of MLM  30 , the inductance of the inductive component decreases. 
   Also, the eddy current generated in the direction of thickness of MLM  30  causes heat generation from the inductive component. However, in the inductive component of this embodiment, MLM  30 &#39;s are formed on the top and the bottom surfaces of coil  21 . As a result, the cross-sectional area per layer of MLM  30  in the direction of the thickness becomes small enough relative to the eddy current. Furthermore, as MLM  30  is formed on the inner wall of THP  22 , the cross-sectional area per layer of MLM  30  in the direction of the thickness is made small enough. As the eddy current generated in the direction of the thickness of MLM  30  can be suppressed, reduction of the flux generated in the direction of the plane of MLM  30  can be prevented. Inductance of the inductive component can be made large in this way. Also, heat generation from the inductive component can be suppressed. 
   On the other hand, it is difficult to form MLM  30  by sputtering or vapor deposition on the inner wall of THP  22  of which the diameter is 1 mm or smaller and the depth is 0.1 mm or greater and 1 mm or smaller, for example. Formation by plating is most preferable. In this way, an inductive component having a large enough inductance is obtainable. As a large enough inductance is obtainable with the inductive component of this embodiment even when designed with a smaller size and a lower profile as noted above, it can be mounted in various small electronic devices such as portable telephones. 
   (Embodiment 2) 
   Referring to  FIG. 6 , a description of an inductive component in Embodiment 2 will now be given. Basic structure of the inductive component is the same as that of the inductive component of Embodiment 1. What is different from embodiment 1 is that the thicknesses of each of magnetic layers  26  that compose MLM  30  are different. In  FIG. 6 , MLM  30  is formed in a manner such that each of magnetic layers  26  is separated by insulating layer  29 . MLM  30  is formed as described below. First, magnetic layer  26  is formed by electroplating on top of a plating under-layer followed by formation of insulating layer  29  by electroplating or electrodeposition. MLM  30  is completed by further sequentially forming a magnetic layer, an insulating layer, and a magnetic layer. In this way, the cross-sectional area per layer of the magnetic layers of MLM  30  is made small enough. Differently from Embodiment 1, MLM  30  to be formed on the inner wall of THP  22  of the inductive component in this Embodiment is formed in the following way. MLM  30  is formed in a manner such that the thickness of each of magnetic layers  26  that compose MLM  30  increases as magnetic layer  26  comes closer to the center of coil  21 . In  FIG. 6 , though MLM  30  has three magnetic layers, the number of layers may be two or four or more. Also, in forming MLM  30 , an under layer similar to plating under-layer  28  may be provided between an insulating layer and a magnetic layer to facilitate formation. 
   A description of the operation of the inductive component as formed above will now be given in the following. When a current is fed to coil  21 , a magnetic flux is generated. This magnetic flux creates a magnetic circuit primarily along the outer wall, the top surface, the bottom surface, and the inner wall of THP  22  of coil  21 . The magnetic flux of the outer side of the magnetic circuit is weaker as the magnetic path length is greater. The magnetic flux generated in the direction of the plane of MLM  30  formed on the inner wall of THP  22  shifts toward the outside of the magnetic circuit formed by MLM  30  as the center of coil  21  becomes nearer. 
   And, as the magnetic path length becomes greater, the magnetic flux becomes weaker. As a result, the flux penetrating MLM  30  formed on the inner wall of THP  22  becomes non-uniform. However, in this Embodiment, each of magnetic layers  26  of MLM  30  formed on the inner wall of THP  22  is formed in a manner such that its thickness increases as the center of coil  21  becomes nearer. As a result, the magnetic resistances of each of magnetic layers  26  are unified. And the magnetic flux penetrating each of magnetic layers  26  of MLM  30  in the direction of the plane will not become weaker as the center of coil  21  becomes nearer. As a result, the magnetic flux that penetrates MLM  30  formed on the inner wall of THP  22  will become uniform thus reducing the leakage flux. As is set forth above, in the inductive component of this Embodiment, the magnetic flux that penetrates MLM  30  formed on the inner wall of THP  22  of coil  21  becomes uniform. As a result, the leakage flux can be reduced and a larger inductance can be obtained. 
   (Embodiment 3) 
   Next, a description of an inductive component in this Embodiment will be given referring to  FIG. 7 . The basic structure of the inductive component is the same as that of the inductive component of Embodiment 1. Difference lies in that the thicknesses of the magnetic layers of corner section  71  consisting of MLM  30  formed on the inner wall of THP  22  of coil  21  and MLM  30  disposed on the top and the bottom surfaces of the coil are made thicker. In  FIG. 7 , corner section  71  is formed in a manner such that the thicknesses of magnetic layers of MLM  30  become thicker. As a result, the cross-sectional area in the direction of the thickness of MLM  30  at corner section  71  is made greater than the cross-sectional area in the direction of the thicknesses of MLM  30  disposed on the top and the bottom surfaces of coil  21  and MLM  30  formed on the inner wall of THP  22 . 
   A description of the operation of an inductive component having the above configuration will now be given below. When a current is fed to coil  21 , a magnetic flux is generated. This magnetic flux forms a magnetic circuit primarily along the outer wall, the top surface, and the bottom surface of coil  21 , and the inner wall of THP  22 . Furthermore, a magnetic flux is also generated in the direction of the plane of MLM  30 . The magnetic flux in the direction of the plane of MLM  30  is easy to leak from the magnetic circuit formed by MLM at corner section  71  of MLM  30  of THP  22  where the magnetic flux concentrates most easily. 
   However, the inductive component in this Embodiment is formed in a manner such that the thicknesses of each of the magnetic layers of MLM  30  at corner section  71  are greater. Accordingly, the cross-sectional area of MLM  30  in the direction of thickness is made greater at corner section  71 , and the magnetic resistance at corner  71  against the magnetic flux that penetrates MLM  30  in the direction of the plane becomes smaller. As a result, leakage from the magnetic circuit formed by MLM  30  at corner section  71  of the magnetic flux that penetrates MLM  30  in the direction of the plane can be prevented. 
   Inductance of the inductive component can be increased in this way. In summary, an inductive component having a large enough inductance is obtainable according to this Embodiment. 
   (Embodiment 4) 
   Next, a description of an inductive component in this Embodiment will be given referring to  FIG. 8 . The basic structure of the inductive component is the same as that of the inductive component in Embodiment 1. However, difference lies in that a recess is provided on insulating material  27  of at least either of the top and the bottom surfaces of THP  22 .  FIG. 8  is an enlarged view of a vicinity of the upper part of THP  22  of the inductive component of this Embodiment. In  FIG. 8 , insulating material  27  is filled in the space formed by MLM  30  inside THP  22 . And a recess is provided on at least either of the top and the bottom surfaces of THP  22 . As insulating material  27 , an organic resin material such as epoxy resin, silicone resin, and acrylic resin is preferable. 
   A description of the operation of the inductive component having the above structure will be given below. When mounting the inductive component of this Embodiment onto a power supply circuit board of an electronic device such as a portable telephone, a finished inductive component is sucked and mounted onto the circuit board. In this process, provision of a recess on at least either the top or the bottom surface of THP  22  of the inductive component facilitates suction. The depth of the recess is as required to facilitate suction and the shallower the better. By providing a recess, falling of the inductive component while being sucked and transferred can be prevented. The inductive components of the first to the fourth Embodiments may be covered with a magnetic material, a metal plate, or a multilayer magnetic layer. Leakage flux can be further reduced by such an arrangement. In this case, a recess for suction may be provided on these magnetic layers. 
   (Embodiment 5) 
   Next, referring to  FIG. 9 , a description will be given on an inductive component of this Embodiment. While the basic structure of the inductive component is the same as that of the inductive component of Embodiment 1, difference lies in that slit  91  is provided in the direction of the plane of MLM  30 . 
   Slit  91  is also provided in the direction of the plane of MLM  30  disposed on the bottom surface of coil  21 , shown in  FIG. 2 . 
   In  FIG. 9 , though four slits  91  are provided, the number may be one, two or more. A description of the operation of an inductive component having the above structure will be given below. When a current is fed to coil  21 , magnetic fluxes are generated in the inductive component. Most of the magnetic fluxes are generated in the direction of the planes of MLM  30  disposed on the top and the bottom surfaces of coil  21 . 
   However, as the inductive component becomes smaller in size and lower in profile, magnetic fluxes are also generated in the directions of the thicknesses of multilayer magnetic layers  30  disposed on the top and the bottom surface of coil  21 . As these magnetic fluxes generate eddy currents in the direction of the plane of MLM  30  disposed on the top and the bottom surfaces, the inductance is reduced. And, the eddy current generated in the direction of the thickness of MLM  30  causes heat generation from the inductive component. However, as the inductive component of this Embodiment has slits  91  in the direction of the plane of MLM  30 , the cross-sectional area of MLM  30  in the direction of the plane can be made small. 
   Consequently, the eddy current generated in the direction of the plane of MLM  30  disposed on the top and the bottom surfaces can be suppressed. In this way, the inductance of the inductive component can be increased. Also, heat generation from the inductive component can be suppressed. Accordingly, an inductive component having a large enough inductance is obtainable even when the size is made smaller and the profile is made lower. The inductive component of this Embodiment has slits  91  in the direction of the plane of MLM  30  disposed on the top and the bottom surfaces of coil  21 . When plating under-layers  28  are to be formed on the top and the bottom surfaces of coil  21 , slits  91  are formed in the direction of the plane of plating under-layers  28 . As a result, cancellation of the magnetic flux generated in the direction of the thickness of plating under-layers  28  can be prevented. Such an arrangement is preferable as the inductance of the inductive component can be increased. Also, heat generation from the inductive component can be suppressed. In this way, an inductive component having large enough inductance is obtainable even when the size is made smaller and the profile is made lower. 
   (Embodiment 6) 
   Referring to  FIG. 10 , a description of an inductive component of this Embodiment will now be given. The basic structure of the inductive component is the same as that of the inductive component of embodiment 1. Difference lies in that slit  92  is formed in the vertical direction from the top to the bottom of MLM  30  formed on the inner wall of THP  22 . The operation of an inductive component having this structure will be given in the following. When a current is fed to coil  21 , magnetic fluxes are generated in the inductive component. Most of the magnetic fluxes are generated in the top and the bottom surfaces of coil  21  and in the direction of the plane of MLM  30  disposed on the inner wall of THP  22 . Furthermore, a vertical magnetic flux is also generated around the center of an empty space formed by MLP  26  in the inner wall of THP  22 . An eddy current is generated in the direction of canceling this magnetic flux, especially in the circumferential direction of annular MLM  30  disposed on the inner wall of THP  22 . As a result, the inductance decreases. 
   However, the inductive component of this Embodiment has slit  92  in the vertical direction of MLM  30  formed on the inner wall of THP  22 . Accordingly, the eddy current in the circumferential direction can be cut and the inductance of the inductive component can be increased. Also, heat generation from the inductive component can be suppressed. While a single vertical slit is provided in  FIG. 10 , needless to say, the number of slits may be two or more. Furthermore, it is preferable to provide in the vertical direction a slit with a thinnest possible thickness from the standpoint of obtaining a high inductance. 
   The width of the slit is in the range 0.01 to 50 μm, preferably 1 to 10 μm. Also, the slit is formed by known methods such as masking-etching method and laser-cut method. 
   In this way, an inductive component having a high enough inductance is obtainable even when the size is made smaller and the profile is made lower. By the way, even when a slit is provided in the lateral direction of MLM  30  formed on the inner wall of THP  22 , it is not possible to cut eddy current in the circumferential direction of MLM  30  formed on the inner wall of THP  22 . 
   INDUSTRIAL APPLICABILITY 
   The inductive components of the present invention have large enough inductance even when the size is made smaller and the profile is made lower. Accordingly, they are most suitable as inductive components for electronic devices that require smaller size and lower profile. They can be used in power supply circuits of portable telephones, for example.