INDUCTOR ELEMENT AND METHOD OF MANUFACTURING THE SAME

Abstract

An inductor element comprises: a ceramic base member; and a coil composed of a conductor having a shape complementary to the ceramic base member. In the inductor element, a prescribed plural number of steps are formed on at least an inner wall surface of the ceramic base member facing to the coil in one direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an inductor element according to an embodiment of the present invention, from which steps on an outer surface are omitted;

FIG. 2 is a perspective view of an inductor element according to an embodiment of the present invention, which shows a coil inside the element;

FIG. 3 is a sectional view of an inductor element according to an embodiment of the present invention, which is taken along a predetermined line of FIG. 1;

FIG. 4 is a perspective view of an inductor element according to an embodiment of the present invention, which shows how a ceramic base member and a coil are separated in a mode of FIG. 3;

FIG. 5 is a perspective enlarged view of a portion A encircled in FIG. 3 of an inductor element according to an embodiment of the present invention;

FIG. 6 is a perspective enlarged view of a portion B encircled in FIG. 5 of an inductor element according to an embodiment of the present invention;

FIG. 7 is a sectional view of an inductor element according to an embodiment of the present invention, which shows a part (one ceramic layer) of a ceramic base member; and

FIG. 8 is a sectional view of an inductor element according to an embodiment of the present invention, which shows a part (one ceramic layer) of a ceramic base member.

EXPLANATION ON SYMBOLS

3 . . . supporting portion, 4 . . . cutout, 5 . . . step, 10 . . . inductor element, 11 . . . cutting line, 12 . . . coil, 13 . . . ceramic base member, 14 . . . ceramic layer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings as appropriate, but the present invention should not be construed as being limited to the embodiment. Those skilled in the art will recognize that the embodiments can be variously changed, adjusted, modified, and replaced on the basis of their knowledge without departing from the scope of the present invention. For example, the accompanying drawings illustrate preferred embodiments of the present invention but the present invention is not limited by modes illustrated in the drawings nor information in the drawings. Similar and equivalent means to those incorporated in the specification are applicable in embodying and examining the present invention, but preferred means are as follows.

FIGS. 1 to 8 each show an inductor element according to an embodiment of the present invention. FIG. 1 is a perspective view of an outer appearance of the inductor element, and FIG. 2 is a perspective view of a coil incorporated in the element. FIG. 3 is a sectional view taken along a cutting line 11 of FIG. 1, and FIG. 4 is a perspective view showing how a ceramic base member and a coil are separated in a mode of FIG. 3. FIG. 5 is a partial enlarged view of a portion A encircled in FIG. 3, and FIG. 6 is a partial enlarged view of a portion B encircled in FIG. 5. FIGS. 7 and 8 are each sectional views of a part of the ceramic base member (one ceramic layer). Refer to coordinate axes in each figure for information on directions in FIGS. 1 to 8.

An inductor element 10 of FIGS. 1 to 8 includes a ceramic base member 13 and a coil 12 formed in the ceramic base member 13 (see FIGS. 3 and 4). The ceramic base member 13 and the coil 12 are complementary in shape (see FIG. 4). The coil 12 made up of a conductor is surrounded by the ceramic base member 13 (magnetic ceramic base member) made of a magnetic member.

The ceramic base member is completed by laminating plural ceramic layers 14. Plural steps 5 are formed on an inner wall surface of the ceramic base member 13 facing to the coil 12 in accordance with a thickness (dimension in a Z direction) of one ceramic layer 14 in the inductor element 10. The dimension of each step 5 is expressed by reference symbol D (see FIG. 7), reference symbol DL (step on the left side of FIG. 8), and reference symbol DR (step on the right side of FIG. 8).

Further, plural steps 5 are formed in the Z direction also on an outer wall surface of the ceramic base member 13, which is not facing to the coil 12 (see FIGS. 3 and 4; omitted from FIG. 5). Further, the steps 5 formed in the Z direction are formed on a surface parallel to an XZ plane as well as a surface parallel to a YZ plane (not shown) of the inner wall surfaces in the inductor element 10.

In the inductor element 10, the ceramic base member 13 and the coil 12 are complementary in shape, and the steps 5 are formed on an inner wall surface of the ceramic base member 13 facing to the coil 12, so steps complementary to the steps 5 formed in the ceramic base member 13 are formed also in the coil 12 (see FIG. 4). Then, in the ceramic base member 13, the steps 5 formed in the Z direction are formed on the surface parallel to the XZ plane as well as to the surface parallel to the YZ plane of the inner wall surfaces, so steps are also formed on a surface parallel to the XZ plane as well as a surface parallel to the YZ plane in the coil 12. The steps are formed on all side surfaces of the coil 12 (see FIG. 2).

As shown in FIGS. 3 and 4, in the inductor element 10, the coil 12 takes a square spiral shape, and its width (dimension in the Y direction) is large, so a resistance generated upon supplying a current in a wiring direction can be reduced. In the inductor element 10, the same coil 12 pattern appears on the XZ plane as a section of the laminated ceramic layers 14. In other words, the coil 12 of the inductor element 10 has such a square spiral shape that a predetermined pattern appears on every section parallel to the XZ plane.

Cutouts 4 are further formed in the same direction as a depth direction of each step 5 on beneath the step 5 in the inductor element 10. The depth direction of each step 5 is an X direction in the step 5 formed on the surface parallel to the YZ plane. In FIG. 5, as for the steps 5 formed on the inner wall surface of the ceramic base member 13 on the left side, the depth direction is a right-handed direction. As for the steps 5 formed on the inner wall surface of the ceramic base member 13 on the right side, the depth direction is a left-handed direction. The dimension of each cutout 4 is expressed by reference symbol KL (cutout on the left side of FIG. 8) and reference symbol KR (cutout on the right side of FIG. 8). In the inductor element 10, the dimension of each cutout 4 is preferably ⅕ to 1/200 of the maximum width of the ceramic base member 13 in the X direction that is the same direction as a depth direction of each cutout 4 (as the depth direction of each step 5). The maximum width of the ceramic base member 13 is denoted by reference symbol W (see FIG. 8).

In the inductor element 10, the steps 5 and the cutouts 4 are formed on both sides of the ceramic base member 13 as described above. The ceramic layers 14 constituting the ceramic base member 13 are not connected but are jointed by a supporting portion 3 at the center. The dimension of the supporting portion 3 is denoted by reference symbol C (see FIG. 8).

Preferred examples of the dimension DL of the step 5 on the left side (of FIG. 8), the dimension DR of the step 5 on the right side, the dimension KL of the cutout 4 on the left side, the dimension KR of the cutout 4 on the right side, the dimension C of the supporting portion 3, and the maximum width W of the ceramic base member 13 are given below.

Example 1

DL=DR=1.6 μm, KL=KR=3.4 μm, C=10 μm, and W=20 μm. In this case, KL (or KR)/W≅1/5.9.

Example 2

DL=DR=1.6 μm, KL=KR=4.9 μm, C=12 μm, and W=25 μm. In this case, KL (or KR)/W≅1/5.1.

Example 3

DL=DR=6 μm, KL=KR=6.5 μm, C=25 μm, and W=50 μm. In this case, KL (or KR)/W≅1/7.7.

Example 4

DL=DR=1.6 μm, KL=KR=2 μm, C=42.8 μm, and W=50 μm. In this case, KL (or KR)/W=1/25.

Example 5

DL=DR=6 μm, KL=KR=20 μm, C=148 μm, and W=200 μm. In this case, KL (or KR)/W=1/10.

Example 6

DL=DR=1.6 μm, KL=KR=2 μm, C=192.8 μm, and W=200 μm. In this case, KL (or KR)/W=1/100.

Further, as for the outer dimension of the inductor element 10, a ratio of a length DX of each step 5 in X direction different from the Z direction in which the steps 5 are formed to a length DZ of each step 5 in the Z direction in which the steps 5 are formed is preferably 0.4 to 1.0. Examples of preferred outer dimension are given below together with available examples of an inductance and a DC resistance.

Example 7

DX=2.6 mm, DY=1 mm, and DZ=3.2 mm. In this case, DX/DZ≅0.81, and DY/DZ≅0.31. As available inductance and DC resistance, inductance L=10 nH and DC resistance R=0.16Ω.

Example 8

DX=0.81 mm, DY=0.61 mm, and DZ=1.6 mm. In this case, DX/DZ≅0.51, and DY/DZ≅0.38. As available inductance and DC resistance, inductance L=1.2 nH and DC resistance R=0.04Ω.

Referring also to FIGS. 1 to 8, a method of manufacturing an inductor element according to the present invention is next described taking as an example the case of manufacturing the inductor element 10 illustrated in FIGS. 1 to 8. In all figures including the coordinate axes, the X axis direction and the Y axis direction (XY plane) correspond to a layer direction of the ceramic layers or ceramic green sheets, and the X axis direction corresponds to a direction in which the ceramic layers or ceramic green sheets are laminated.

A first embodiment of manufacturing an inductor element according to the present invention is described first. To manufacture the inductor element 10, 12 ceramic green sheets (see FIGS. 3 and 4) having a predetermined shape and a predetermined thickness and mainly made of a ceramic material are prepared first. The ceramic green sheets (also simply referred to as “sheets”) can be manufactured by a conventional ceramic manufacturing method. For example, powder of a magnetic ceramic material is prepared and mixed with a binder, a solvent, a disperser, a plasticizer, or the like at a desired blending ratio to prepare a slurry, followed by degassing to thereby form a sheet by a sheet forming process such as a doctor blade process, a reverse roll coater process, or a reverse doctor roll coater process. Incidentally, a size and shape of the ceramic green sheet may be determined in accordance with a target size of the inductor element.

Next, holes of a predetermined shape are formed in each of the resultant 12 ceramic green sheets by a punching machine including a punch and a die to complete the ceramic green sheets each having a hole formed therein. The respective holes formed in each of the ceramic green sheets form a cavity in such a way that the ceramic green sheets are laminated to form collectively a hole as a whole. The shape of the hole in each ceramic green sheet is set so that the cavity shape corresponds to a desired shape of the coil 12.

Next, the ceramic green sheets with the holes are laminated one on top of the other to form a green laminate. In the resultant green laminate, a hole is formed as a whole to define a cavity corresponding to the shape of coil 12. Thus, if the green laminate is fired, the ceramic base member 13 that serves as a die and has a cavity corresponding to the shape of coil 12 and defined by the cumulatively formed hole is obtained. Twelve sheets of ceramic green sheets are backed to form the ceramic layers 14 composed of twelve laminated punched sheets to thereby complete the ceramic base member 13. At this point, the coil 12 is not yet formed in the ceramic base member 13.

Subsequently, a conductive material is filled by, for example, a dispensing method into the cavity of the ceramic base member 13 that serves as a die and the resultant is fired, thereby the conductive material is formed into the coil 12 and the inductor element 10 is completed. Incidentally, the formation of terminals for establishing connections with the outside or coverage (sealing) with a protective film (insulating film) is optionally performed (the same thing is applicable to the following second embodiment of manufacturing an inductor element according to the present invention, so repetitive description thereof is omitted below).

If the first embodiment of manufacturing an inductor element according to the present invention is used, the coil 12 shape is determined by the cavity shape, and the cavity shape is determined by the hole shape and the thickness of the ceramic green sheet (ceramic layer 14), so these are important in manufacturing an inductor element according to the present invention with the first embodiment of manufacturing an inductor element according to the present invention. In other words, the shape of the coil 12 is determined by the thickness of one ceramic layer 14 (ceramic green sheet before firing in a manufacturing process) and the shape of the hole formed in one ceramic layer 14 (ceramic green sheet before firing in a manufacturing process). Hence, in the first embodiment of manufacturing an inductor element according to the present invention, it is desirable to set the thickness of the ceramic green sheet (fired ceramic layer 14) in accordance with an intended shape of the coil 12 of the inductor element 10.

According to the first embodiment of manufacturing an inductor element of the present invention, the cavity for forming the coil 12 is defined by the hole collectively formed from each hole formed in each green sheet by punching process as a result of lamination. The hole formed in every sheet by the punching process is tapered due to a difference in dimension between an opening at the inlet and an opening at the outlet (in general, smaller at the outlet). Thus, the step 5 corresponding to the thickness of one ceramic layer 14 is formed on the cavity formation surface (wall surface) of the ceramic base member 13 as a laminate of the ceramic layers 14 formed by firing the sheets (see FIGS. 3 and 4).

Next, the second embodiment of manufacturing an inductor element according to the present invention is described. To manufacture the inductor element 10, 12 ceramic green sheets (see FIGS. 3 and 4) having a predetermined shape and a predetermined thickness and mainly made of a ceramic material are prepared first. The ceramic green sheets can be manufactured by a conventional ceramic manufacturing method as described above.

Next, the hole of a predetermined shape is formed in each of the resultant 12 ceramic green sheets by a punching machine including a punch and a die, and in addition, a conductive material for forming a part of the coil 12 is filled into each hole by a printing method using metal mask photolithography. Through the above steps, the ceramic green sheets having a hole, respectively formed therein and filled with a conductive material are obtained. The hole formed in the respective ceramic green sheets serves as a part to form collectively a cavity by laminating a prescribed number of ceramic green sheets. The conductive material filled into each hole formed in each ceramic green sheet forms a coil 12 as a result of laminating the ceramic green sheets so as to form a hole collectively.

Next, the ceramic green sheets with the holes filled with the conductive material are laminated one on top of the other to form a green laminate. In the resultant green laminate, a hole is collectively formed to define a cavity corresponding to the coil 12 shape. At this point, the conductive material for forming the coil 12 later is already filled in the cavity. Thus, if the green laminate is fired, the conductive material is formed into the coil 12 to complete the inductor element 10. The 12 ceramic green sheets are backed to form the 12 ceramic layers 14 to thereby complete the ceramic base member 13.

Even in the second embodiment of manufacturing an inductor element according to the present invention, similar to the first embodiment of manufacturing an inductor element according to the present invention, the coil 12 shape is determined by the cavity shape, and the cavity shape is determined by the hole shape and the thickness of the ceramic green sheet (ceramic layer 14), so these are important in manufacturing an inductor element according to the present invention with the second embodiment of manufacturing an inductor element according to the present invention. In other words, the shape of the coil 12 is determined by the thickness of one ceramic layer 14 (ceramic green sheet before firing in a manufacturing process) and the shape of the hole formed in each ceramic layer 14 (ceramic green sheet before firing in a manufacturing process). Hence, in the second embodiment of manufacturing an inductor element according to the present invention, it is desirable to set the thickness of the ceramic green sheet (fired ceramic layer 14) in accordance with an intended shape of the coil 12 of the inductor element 10.

Even in the second embodiment of manufacturing an inductor element according to the present invention, the cavity for forming the coil 12 is defined by the hole formed collectively from a hole in each green sheet by a punching process. The hole formed in the sheet by the punching process is tapered due to a difference in dimension between an opening at the inlet and an opening at the outlet (in general, smaller at the outlet). Thus, the step 5 corresponding to the thickness of each ceramic layer 14 is formed on the cavity formation surface (wall surface) of the ceramic base member 13 as a laminate of the ceramic layers 14 formed by firing the sheets (see FIGS. 3 and 4).

In the inductor 10 manufactured by the first or second method of manufacturing an inductor element according to the present invention, the wall portion (real portion) of the ceramic base member 13 that defines the cavity is formed by laminating the ceramic layers 14, and the hole in the ceramic layer 14 (ceramic green sheet before firing in a manufacturing process) can be formed into a simple rectangular shape. Thus, it can be easily formed with a very small thickness. Thus, according to the method of manufacturing an inductor element of the present invention, it is possible to manufacture an inductor element having the coil 12 that occupies a large area of the entire circuit area in the compact size with ease.

Next, materials used for the inductor element according to the present invention are described. As a material (ceramic material) for the ceramic base member (ceramic layer), a magnetic ceramic material of a spontaneous magnetization function, which mainly contains iron oxide, can be used. Examples thereof include a soft magnetic material as spinel-structure ferrite and garnet-structure ferrite, and a hard magnetic material as magnetoplum bite structure ferrite. Specific examples thereof include a material made of oxides of an iron group element generally called “ferrite” (MFe.O₃ in a molecular formula), which is a solid solution of Zn-ferrite such as Mn-ferrite or Ni-ferrite (ZnFe₂O₄).

As a coil material, conductive noble metal is used. Examples thereof include Ag, Au, Pd, and Pt. Incidentally, the conductive material is mixed with a binder when in use (filled and formed). Examples of the binder include glass fine particles mainly containing oxides such as SiO₂, B₂O₃, Na₂O, PbO, or ZnO.

In the case of partially or completely covering the inductor with a protective film, silicon dioxide, silicon nitride, borophosphosilicate glass (BPSG), and phosphosilicate glass (PSG) may be used as a material for the protective film.

Claims

1. An inductor element, comprising: a ceramic base member; anda coil composed of a conductor having a shape complementary to the ceramic base member,wherein a prescribed plural number of steps are formed on at least an inner wall surface of the ceramic base member facing to the coil in one direction.

2. The inductor element according to claim 1, wherein a cutout is formed beneath of each of the steps in the same direction as a depth direction of each of the steps.

3. The inductor element according to claim 2, wherein the cutout has a dimension that is ⅕ to 1/200 of the maximum width of the ceramic base member in the same direction as a depth direction of the cutout.

4. The inductor element according to claim 2, wherein the cutout has a dimension of 2 to 20 μm.

5. The inductor element according to claim 3, wherein the cutout has a dimension of 2 to 20 μm.

6. The inductor element according to claim 1, wherein the inductor element has a square spiral shape.

7. The inductor element according to claim 1, wherein a ratio of a length of each of the prescribed plural number of steps in another direction different from the one direction in which the prescribed plural number of steps is formed to a length of each of the prescribed plural number of steps in the one direction is 0.4 to 1.0.

8. The inductor element according to claim 6, wherein a ratio of a length of each of the prescribed plural number of steps in another direction different from the one direction in which the prescribed plural number of steps is formed to a length of each of the prescribed plural number of steps in the one direction is 0.4 to 1.0.

9. The inductor element according to claim 1, wherein the ceramic base member is a magnetic ceramic base member composed of a magnetic member.

10. A method of manufacturing an inductor element, comprising: preparing a prescribed plural number of ceramic green sheets;punching out a hole of a predetermined shape in each of the ceramic green sheets;laminating the prescribed plural number of ceramic green sheets each having the hole to form a green laminate;firing the green laminate to form a ceramic base member that serves as a form including a cavity that is defined as a coil shape by the holes;filling a conductive material into the cavity of the ceramic base member that serves as a form;firing the ceramic base member; andintegrally forming a coil in the cavity.

11. A method of manufacturing an inductor element, comprising: preparing a prescribed plural number of ceramic green sheets;punching out a hole of a predetermined shape in each of the ceramic green sheets;filling the hole with a conductive material;laminating the prescribed plural number of ceramic green sheets each having the hole filled with the conductive material to form a green laminate; andfiring the green laminate to form a ceramic base member where a coil is integrally formed in a cavity of a coil shape defined by the holes.

12. The method of manufacturing an inductor element according to claim 10, wherein the ceramic green sheet is a magnetic ceramic green sheet composed of a magnetic ceramic material.

13. The method of manufacturing an inductor element according to claim 11, wherein the ceramic green sheet is a magnetic ceramic green sheet composed of a magnetic ceramic material.