JP2000269035A - Planar magnetic element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a planar magnetic element, such as a planar inductor, capable of reducing the effects of the magnetic saturation of a magnetic material and superior in DC superimposing characteristics. SOLUTION: This planar magnetic element comprises a planar coil 13, having a coil structure such that longitudinal single spiral coils 131 and 132 are arranged side by side with their longer sides extend in parallel with each other, and a pair of magnetic films 15 and 11 interposing the upper and lower sides of the coil 13 through insulating films 14 and 12, respectively. The conductors of the coils 131 and 132 are arranged, such that the direction of the current flowing through one of the coils is made opposite to the direction of the current flowing through the other coil. The easy axis of magnetization of the coil is formed so as to extend in the direction of the longer side. Superior current superposition characteristics and high inductance density can be obtained at the same time. This planar magnetic element can be applied to DC/DC converters and transformers.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic passive element, and more particularly to a planar magnetic element using a planar coil.

[0002]

2. Description of the Related Art In recent years, various electronic devices have been actively miniaturized, and accordingly, various devices have been produced by using a thin film process. In this process, magnetic elements such as inductors, transformers, and magnetic heads are wound on a conventional bulk magnetic material, while a flat coil having a spiral or zigzag pattern is covered with a magnetic material. Planar inductors having an iron-type structure have been proposed (for example, IEEE Trans., Magn., MA).
G-20, no. 5, pp. 1804-1806). On the other hand, as seen in the example of a DC-DC converter for a small electronic device, there is an increasing demand to operate at a frequency of MHz or more in order to reduce the size and weight. Among them, the high-frequency inductor is one key component,
There are demands for (1) small size and light weight, (2) good frequency characteristics, and (3) appropriate power capacity.

[0003]

However, in the current high-frequency planar inductor, although the improvement in the frequency characteristics is seen, it cannot be said that the required characteristics are satisfied because the power capacity is small. . When an inductor is used as a choke coil, a DC current corresponding to a load current and an AC current due to switching of a semiconductor switch flow. The choke coil is required to have a DC superposition characteristic in which electrical characteristics such as inductance are constant even when a large DC current is superimposed. However, when the DC superimposed current increases, when the operating point of the magnetic body reaches the saturation region of the BH curve, the incremental magnetic permeability decreases, so that the inductance sharply decreases. In particular, in a planar inductor, a coil conductor and a magnetic body are very close to each other in order to obtain a large inductance per unit area, and a generated magnetic field becomes large even with a small coil current. As a result, the magnetic body is liable to cause magnetic saturation. With reference to FIG. 10, a description will be given of a conventional planar inductor composed of a conventional double spiral planar coil using plated Cu as a conductor, insulator layers provided on both surfaces thereof, and magnetic material layers provided on both surfaces thereof. (INTELEC 96 Proceedings
p485-490 (1996)). The planar inductor 5 is configured by combining a rectangular first single spiral coil 3 and a second single spiral coil 4.

[0004] The first single spiral coil 3 has an electrode pad 1 at the center of the coil, from which four plated copper conductors are led out, wound counterclockwise, and the second adjacent spiral coil is wound. It is connected to the single spiral coil 4. This plated copper conductor is wound clockwise from the outside to the center from the first single spiral coil 3 to the second single spiral coil 4 and is connected to the electrode pad 2 at the center. That is, the two coils are wound in opposite directions. The conductor constituting this single spiral coil has a width of 35 μm and a thickness of 50 μm.
m, the interval between conductors is 50 μm, and the number of turns is 3 turns on one side (6 turns at the center). For example, an insulator layer made of an organic material such as polyimide or fluororesin has a thickness of 5 μm. Magnetic material such as ferrite has a thickness of 6
μm (1.5 μm, 4 layers laminated, insulating film thickness between laminated magnetic films 0.4 μm), saturation magnetic flux density 1.6T, magnetic permeability 1143
(Measured value on a smooth magnetic film). The DC superposition characteristics of the planar inductor 5 are as shown in FIG. FIG.
1, the vertical axis represents the inductance L (μH), and the horizontal axis represents the DC superimposed current Idc (A). The maximum current Im when using the DC current value when the inductance is reduced by 5%.
amax, the maximum current Imax in this case is 0.3
A. This is determined because the magnetic material is magnetically saturated and the effective magnetic permeability is reduced.

[0005] The problem of the DC superposition characteristic is important not only in the case of the inductor for the choke coil but also in the case of the transformer. For example, forward type or flyback type DC-D
In the transformer for the C converter, since a unipolar pulse voltage is applied to the primary coil, a sudden decrease in inductance due to magnetic saturation is a problem. In addition, push bull type DC
In the -CD converter, the voltage applied to the transformer is, in principle, positive / negative symmetric, but the positive / negative ON time fluctuates due to variations in switching transistor characteristics and the transformer is demagnetized. Is a problem. If the influence of the magnetic saturation of the magnetic material of the planar inductor or the transformer can be reduced, the DC superposition characteristics can be improved. The present invention has been made in view of such circumstances, and provides a planar magnetic element such as a planar inductor which can reduce the influence of magnetic saturation of a magnetic material and has excellent DC bias characteristics.

[0006]

According to the present invention, there is provided a flat coil having a coil structure in which two vertically long single spiral coils are arranged so that long sides thereof are parallel to each other, and an insulating film is formed on and under the flat coil. The conductors of these two single spiral coils have a plane magnetic element arranged so that the directions of currents flowing in the coils are opposite to each other. The easy axis is formed in the long side direction.
Excellent DC superimposition characteristics and high inductance density can both be achieved. The planar magnetic element of the present invention has DC-
Used for DC converters and transformers.

That is, a planar magnetic element according to the present invention comprises a planar coil and a pair of magnetic films sandwiching the planar coil above and below via an insulating film, wherein the planar coil includes first and second coils. The second rectangular single spiral coils are arranged such that the long sides thereof are opposed to each other, and the conductors of the adjacent first single spiral coil and the conductor of the second single spiral coil are in the direction of the current flowing therethrough. Are arranged to be opposite to each other. The planar coil may have an axis of easy magnetization formed in a long side direction. A slit is formed in the magnetic film formed on the planar coil via the insulating film, and the slit is disposed at a center of each of the first and second single spiral coils in a long side direction. It may be done. The first and second single spiral coils have electrode pads, and the insulating film and the magnetic film laminated on the planar coil have openings formed to expose the electrode pads. You may do it.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. Here, the planar magnetic element according to the present invention relates to a planar inductor. Among the same planar magnetic elements, a planar transformer is basically the same as a planar inductor except that two planar coils of a primary coil and a secondary coil are stacked, and the effect obtained by the present invention is also the same. Therefore, the description is omitted. First, a first embodiment will be described with reference to FIGS. FIG. 1 is a perspective view of a planar inductor. In this inductor, both surfaces of a rectangular planar coil are sandwiched between insulating films, and the insulating films are further sandwiched between magnetic films. Uniaxial magnetic anisotropy is introduced into the upper and lower magnetic films.

On a base substrate 10 made of a glass substrate, a ceramic substrate, a silicon wafer or the like, for example, N
First uniaxial magnetic anisotropy made of i-Zn ferrite
Ferrite magnetic film 11 is formed. A metal such as zirconium or copper can be used for the base substrate. However, since the metal material may diffuse into the magnetic film, the surface is preferably covered with a diffusion preventing film such as silicon oxide. The first ferrite magnetic film 11 is covered with a first insulating film 12. For the first insulating film 12, an organic insulating material such as polyimide or fluorine resin or an inorganic insulating material such as an insulating plate or a ceramic plate obtained by firing a glass paste in which glass is dispersed is used. A square planar coil 13 is formed on the first ferrite magnetic film 11 with the insulating film 12 interposed therebetween. The planar coil 13 includes first and second rectangular single spiral coils 13.
1 and 132 are arranged such that the long sides thereof are opposed to each other, and the conductors of the adjacent first single spiral coil 131 and the conductor of the second single spiral coil 132 have opposite current directions. (Hereinafter, such a configuration which is a feature of the present invention is referred to as a twin spiral coil). The planar coil 13 of this embodiment, which is called a twin spiral coil, uses, for example, copper as a material. The first single spiral coil 131 is connected to the first electrode pad 1
33 and a second single spiral coil 132
Has a second electrode pad 134.

[0010] The planar coil 13 is covered with a second insulating film 14. The second insulating film 14 may be made of the same material as the first insulating film 12, or may be made of a different material. An opening 141 is formed in the second insulating film 14. The opening 141 is arranged so as to surround the electrode pads 133 and 134 formed below the second insulating film 14. On the second insulating film 14, for example, Ni-Z
n ferrite, Mn-Zn ferrite, Cu-Ni-Z
A uniaxial magnetic anisotropic second ferrite magnetic film 15 made of n ferrite or the like is formed. An opening 151 is formed in the second ferrite magnetic film 15. The opening 151 coincides with the opening 141 of the second insulating film 14, and the electrode pads 133 and 134 are exposed inside. The electrode pad is connected to an external terminal via these openings. A slit 152 is formed in the second ferrite magnetic film 15 so as to penetrate the opening 151. The slit 152 overlaps the center of the first and second single spiral coils 131 and 132 in the long side direction.

FIG. 2 shows the direction of the magnetic field generated on the ferrite magnetic film 11 when a coil current flows through the planar coil 13 of the planar inductor shown in FIG. First single spiral coil 131 and second single spiral coil 132 constituting planar coil 13
Have a coil structure in which vertically elongated single spiral coils are arranged so that their long sides are parallel. First single spiral coil 131
, The coil is wound counterclockwise from the center, and the second single spiral coil 132 is wound clockwise from the center. Therefore, the electrode pads 133, 13
When a current flows between the conductors 4, the conductors of the adjacent first single spiral coil 131 and the conductor of the second single spiral coil 132 have opposite current directions. The planar coil 13 has an easy axis of magnetization in a long side direction as indicated by an arrow, and a hard axis of magnetization in a short side direction. In the planar coil of FIG. 2, in the region A of the magnetic film 11 formed along the short side, the direction of the magnetic field generated by the coil current indicated by the arrow and the easy axis direction of uniaxial magnetic anisotropy are parallel. . On the other hand, the magnetic film 1 which is a region other than the region A
In the area B, the direction of the magnetic field generated by the coil current is perpendicular to the easy axis direction of the uniaxial magnetic anisotropy.

FIG. 3 is a characteristic diagram showing BH curves of the magnetic film having uniaxial magnetic anisotropy in the easy axis direction and the hard axis direction. Although the magnetic permeability is very high in the direction of the easy magnetization, it is easily saturated, and is hardly saturated in the direction of the hard magnetization. Therefore, the region A shown in FIG. 2 is easily saturated, but the region B is hardly saturated. FIG. 4 is a characteristic diagram showing the DC superposition characteristics of the respective inductances when the magnetization in the easy axis direction (curve A) and the magnetization in the hard axis direction (curve B) of the twin spiral coil of the present invention are performed. This is when the excitation is performed at a frequency lower than MHz, and when the operation is performed at a higher frequency, the inductance value in the case of the magnetization in the easy axis direction rapidly decreases with the frequency. As shown by a curve C, the DC superposition characteristic of the inductance when the hard axis excitation of the conventional double spiral coil (see FIG. 10) is performed is deteriorated even if the inductance characteristic is good. In the present invention, since the structure of the planar coil is a twin spiral coil or a twin coil in which two vertically long single spiral coils are arranged side by side, both the inductance density and the DC superimposition characteristics are improved.

Next, a second embodiment will be described with reference to FIGS. 5, 6, 8 and 9. FIG. 5 shows a planar coil (twin spiral coil or twin coil) of the present invention.
FIG. The planar coil 20 includes first and second coils.
Rectangular single spiral coils 21 and 22 are arranged such that their long sides face each other, and the conductor of the adjacent single spiral coil 21 and the conductor of the second single spiral coil 22 determine the current flowing therethrough. They are arranged and formed so that their directions are opposite to each other. These single spiral coils 21 and 22 have electrode pads 23 and 24, respectively. This planar coil 2
The conductor constituting 0 has a width of 35 μm, a thickness of 50 μm, an interval between the conductors of 50 μm, 8 turns on each side (16 turns at the center), and an insulating film (not shown) sandwiching the planar coil 20 has a film thickness. 5 μm, a plane coil 20 via an insulating film
The magnetic film (not shown) sandwiching the film has a thickness of 6 μm (1.5 μm).
m, four-layer laminate, insulating film thickness between laminated magnetic films is 0.4 μm), saturation magnetic flux density is 1.6 T, and magnetic permeability is 850. The electrode pads 23 and 24 have a width of 455 μm.

At this time, the maximum current Ima when the DC current is used
x is 0.63 A, and the inductance is 4.05 m in width.
0.38μH per device unit length of m
The inductance density per vice unit area is 0.0
94μH / mm^TwoIt is. Similarly, a planar coil (twin
(Spiral coil) 20 turns with 6 turns per side
(12 turns at the center), the maximum current I
The max is 0.87 A and the inductance is 3.3 in width.
0.21 μH per 7 mm device unit length,
The inductance density per actual device unit area is 0.
062 μH / mm ^TwoIt is. In addition, the number of turns is 10
(20 turns at the center), the maximum current
The Imax is 0.55 A, and the inductance is 4.
0.59 μH per 73 mm device unit length
The inductance density per unit area of the actual device is
0.12 μH / mm^TwoIt is. FIG. 6 shows the second embodiment.
FIG. 5 is a characteristic diagram showing characteristic values of a planar coil, where the horizontal axis indicates
Ductance density (μH / mm^Two), Vertical axis uses DC current
It is displayed as the maximum current Imax (A) at the time. This implementation
The characteristic curve of the example is represented by characteristic curve A.

On the other hand, in the flat coil using the conventional double spiral coil shown in FIG. 8, the maximum current Imax obtained with the same coil specifications, insulating film thickness and magnetic film magnetic characteristics is 0.34 A. Yes, inductance is width 4.
It is 0.61 μH per unit length of the device of 05 mm, and the inductance density per unit area of the actual device is 0.15 μH / mm ² . The characteristic curve of the double spiral coil shown in FIG. When the double spiral coil is used, the inductance density increases, but the maximum current Imax decreases. Similarly, when a double spiral coil is used and the number of turns is 6 turns on one side (12 turns at the center), the maximum current Imax is 0.40 A and the inductance is 0.33 mm per device unit length of 3.37 mm.
8 μH, and the inductance density per unit area of the actual device is 0.11 μH / mm ² . Furthermore, when the number of turns is 4 turns on one side (8 turns at the center), the maximum current Imax is 0.54 A, and the inductance is 0.19 μH per unit length of a 2.69 mm wide device.
And the inductance density per unit area of the actual device is 0.07 μH / mm ² .

In the conventional planar coil using a double spiral coil shown in FIG. 8, a planar coil 5 'has first and second rectangular single spiral coils 3' and 4 'whose long sides are opposed to each other. The conductors of the adjacent first single spiral coil 3 'and the conductors of the second single spiral coil 4' are arranged and formed so that the direction of the current flowing therethrough is the same. These single spiral coils 3 ', 4' have electrode pads 1 ', 2', respectively. On the other hand, the flat coil 5 ″ using the conventional single spiral coil shown in FIG. 9 has a maximum current Imax of 0.6 when using a DC current obtained by the same coil specifications, insulating film thickness, and magnetic characteristics of the magnetic film.
6A, the inductance is 0.18 μH per unit length of the device having a width of 2.59 mm, and the inductance density per unit area of the actual device is 0.070 μH / m.
m ² . Similarly, the flat coil 5 ″ using a single spiral coil and having six turns per side (12 turns at the center) has a maximum current Imax of 0.93.
A, the inductance is 0.28 μH per unit length of the device having a width of 2.25 mm, and the inductance density per unit area of the actual device is 0.043 μH / mm.
²

Further, the planar coil 5 "having 10 turns per side (20 turns at the center) has the maximum current Imax of 0.52 A and an inductance of width 2.
It is 0.28 μH per unit length of 93 mm device, and the inductance density per actual device unit area is 0.097 μH / mm ² . This characteristic curve is represented by a characteristic line C. The conventional planar coil 5 "using a single spiral coil shown in Fig. 9 is formed of a rectangular single spiral coil, and has electrode pads 1" and 2 "at both ends of the coil conductor. In comparison, the twin spiral structure (characteristic line A) of the present invention has both the maximum current Imax and the inductance density as compared with the conventional double spiral structure (characteristic line B) and single spiral structure (characteristic line C). Can be increased together.

This can be explained as follows. The double spiral coil has, for example, a magnetic flux density distribution as shown in FIG. In FIG. 12, the horizontal axis represents the in-plane position of the magnetic film, and the vertical axis represents the magnetic flux density. This magnetic flux density indicates the magnetic flux density distribution of the in-plane direction component of the portion along the line LL 'of the magnetic film of the magnetic element shown in FIG. The horizontal axis is
The left end (L) and right end (L ') of the magnetic film are parallel to the direction of the hard axis of the coil. In the double spiral coil, the absolute value of the magnetic flux density becomes large because the direction of the current of the first coil and the direction of the second spiral coil coincide in the coil at the center. On the other hand, the magnetic flux densities near the right and left coils do not increase as in the center.
For this reason, the inductance is not so large, but the DC superimposition characteristics are improved. On the other hand, the twin spiral coil has a magnetic flux density distribution as shown in FIG. FIG.
The horizontal axis represents the in-plane position of the magnetic film, and the vertical axis represents the magnetic flux density. This magnetic flux density indicates the magnetic flux density distribution of the in-plane direction component of the portion along the line LL 'of the magnetic film of the magnetic element shown in FIG. The horizontal axis represents the left end (L) and the right end (L ') of the magnetic film parallel to the direction of the hard axis of the coil. In the twin spiral coil, the coil at the center also shows the same magnetic flux density distribution as the right and left coils (however, the sign and the direction are reversed), so that the DC superimposition characteristics as well as the inductance are improved. Further, in the case of a single spiral coil, the number of pads is twice that in the case of a twin spiral coil, so that the inductance density is reduced.

Next, a third embodiment will be described with reference to FIGS. The planar coil according to the present invention is constituted by a twin spiral coil or a twin coil, and the first and second rectangular single spiral coils are arranged such that their long sides are opposed to each other, and the adjacent first single spiral coil is arranged. And the conductor of the second single spiral coil are arranged and formed such that the directions of currents flowing therethrough are opposite to each other. Each of these single spiral coils has an electrode pad.
The conductor constituting the planar coil has a width of 90 μm and a thickness of 60 μm.
μm, the spacing between conductors is 30 μm, the number of turns is 8 turns per side (16 turns at the center), and is made of plated copper.
The insulating film sandwiching the planar coil has a thickness of 5 μm, and the magnetic film sandwiching the planar coil via the insulating film has a thickness of 6 μm (1.5 μm).
μm, 4 layers stacked, insulating film thickness between stacked magnetic films 0.4 μm),
An FeCoBC-based amorphous magnetic film having a characteristic of a saturation magnetic flux density of 1.6 T is used. The electrode pad has a width of 480
μm. The outer shape of a planar inductor formed using this planar coil is 5.48 × 5.8 mm.

FIG. 7 is a characteristic diagram showing a DC current superposition characteristic of the planar inductor. The inductance when the DC current is 0 A is 1.27 μH, and the DC current when the inductance is reduced by 5% is 0.62 A. At this time, the inductance in a region where the coils are linearly arranged and the coil current coincides with the direction of the easy axis of magnetization of the magnetic film is 0.337 μH / mm per unit length. Inductor width converted to conductor width of 35 μm / interconductor distance of 50 μm is 3.97 mm
And the inductance density per unit area is 008.
5 μH / mm ² . This is point D shown in FIG.
It is possible to obtain a combination of the inductance density and the DC superimposition characteristic, which cannot be obtained by the conventional single spiral coil and double spiral coil.

[0021]

As described above, both the DC bias characteristics and the inductance density can be maintained large. Therefore, when a magnetic element using the coil structure of the present invention is used, a small-sized magnetic element having excellent DC bias characteristics can be obtained. This magnetic element is DC
-Applied to DC converters and transformers.

[Brief description of the drawings]

FIG. 1 is a perspective view of a magnetic element of the present invention.

FIG. 2 is a plan view illustrating a relationship between a magnetic field generated by a coil current and a direction of uniaxial anisotropy in the magnetic element of the present invention.

FIG. 3 is a characteristic diagram showing magnetic field hysteresis curves in an easy axis direction and a hard axis direction.

FIG. 4 is a DC superposition characteristic diagram of a magnetic element when an easy axis direction and a hard axis direction are main excitation directions.

FIG. 5 is a plan view of a coil structure of a twin spiral coil of the present invention.

FIG. 6 is a characteristic diagram showing a relationship between the inductance density and Imax of a magnetic element using the twin spiral coil of the present invention.

FIG. 7 is a characteristic diagram showing DC current superposition characteristics of the planar inductor of the present invention.

FIG. 8 is a coil structure plan view of a conventional double spiral coil.

FIG. 9 is a plan view of a coil structure of a conventional single spiral coil.

FIG. 10 is a plan view of a coil structure forming a conventional inductor.

FIG. 11 is a characteristic diagram showing a DC superposition characteristic of the inductor.

FIG. 12 is a characteristic diagram showing a magnetic flux density distribution at an in-plane position of a magnetic film in a conventional magnetic element.

FIG. 13 is a characteristic diagram showing a magnetic flux density distribution at an in-plane position of a magnetic film in the magnetic element of the present invention.

[Explanation of symbols]

1, 1 ', 1 ", 2, 2', 2", 23, 24, 13
3, 134 ... electrode pad, 3, 3 ', 21, 131 ... first single spiral coil, 4, 4', 22, 132 ... second single spiral coil, 5, 5 ', 5 ″, 13 ... Planar coil, 10.
..Underlying substrate, 11: first ferrite magnetic film, 12: first insulating film, 14: second insulating film, 15: second ferrite magnetic film, 141, 151 ... opening, 152 ... slit.

Claims (4)

[Claims] 1. A flat coil comprising: a planar coil; and a pair of magnetic films sandwiching the planar coil above and below via an insulating film, wherein the planar coil includes first and second rectangular single spiral coils. Are arranged so that their long sides face each other,
A planar magnetic element, wherein adjacent conductors of the first single spiral coil and conductors of the second single spiral coil are arranged so that the directions of currents flowing therethrough are opposite to each other. 2. The planar magnetic element according to claim 1, wherein the planar coil has an axis of easy magnetization formed in a long side direction. 3. A slit is formed in the magnetic film formed on the planar coil with the insulating film interposed therebetween, and the slit is formed in a long side direction of the first and second single spiral coils. The planar magnetic element according to claim 1, wherein the planar magnetic elements are arranged at respective centers. 4. The first and second single spiral coils have electrode pads, and the insulating film and the magnetic film laminated on the planar coil have openings for exposing the electrode pads. The planar magnetic element according to any one of claims 1 to 3, wherein is formed.