JPH04368105A - Planar inductor - Google Patents

Abstract

PURPOSE:To obtain a planar inductor having large inductance and excellent DC superposition characteristics. CONSTITUTION:In a planar inductor wherein a plurality of ferromagnetic material layers 5a-5f are formed on both surfaces of spiral coils 2a, 2b, via insulating layers, the ferromagnetic layers 5a-5f have magnetic anisotropy having an uni- axis of easy magnetization in the direction perpendicular to magnetic flux. The magnitude of magnetic anisotropy becomes small as the distance from the spiral coils 2a, 2b increases.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a planar inductor.
In particular, the present invention relates to a planar inductor with improved DC superimposition characteristics.

0002

2. Description of the Related Art Conventionally, planar inductors are known in which a spiral conductor coil is sandwiched between ferromagnetic layers with an insulating layer interposed on both sides. An example of such a planar inductor is shown in FIGS. 5A and 5B. Note that (A) is a plan view of this planar inductor, and (B) is a plan view of this planar inductor.
) is a sectional view taken along line AA'.

In FIGS. 5A and 5B, a spiral conductor coil 1 includes spiral coils 2a and 2b provided on both sides of an insulating layer 3b, and these spiral coils 2a and 2b.
b electrically through through hole 4 and spiral coil 2
It has a structure in which the terminals a and 2b are connected so that currents flow in the same direction. Here, the solid line and the broken line in FIG. 5A represent the loci of the centers of the spiral coils 2a and 2b on the front and back sides of the insulating layer 3b, respectively. A planar inductor is constructed by sandwiching both surfaces of this spiral conductive coil 1 between ferromagnetic layers 5a and 5b with insulating layers 3a and 3c interposed therebetween. An inductance is formed between the terminals 6a and 6b of the planar inductor made of the above members.

The above-mentioned planar inductor is, for example, DC-D.
Applicable to output choke coils of C inverters, etc. In this case, since a high frequency current with a superimposed direct current flows through the planar inductor, good direct current superimposition characteristics are required. However, conventional planar inductors have a problem in that they do not have sufficient DC superimposition characteristics. Therefore, Fe is added to the ferromagnetic material.
It is possible to use materials with high saturation magnetization such as amorphous alloys, but this cannot be said to be effective when a large direct current is superimposed.

[0005]

SUMMARY OF THE INVENTION As described above, conventional planar inductors have had the problem of insufficient DC superimposition characteristics. The present invention takes the above-mentioned problems into consideration, and aims to improve the DC superimposition characteristics of a planar inductor.

[0006]

Means for Solving the Problems and Effects In order to achieve the above object, the present invention provides a planar inductor in which a laminate consisting of a plurality of ferromagnetic layers is provided on both sides of a spiral coil with an insulating layer interposed therebetween. The ferromagnetic layer has magnetic anisotropy with a uniaxial magnetic easy axis in a direction perpendicular to the magnetic flux, and the magnitude of the magnetic anisotropy decreases as the distance from the spiral coil increases. The present invention provides a planar inductor characterized by the following.

The spiral coil in the planar inductor of the present invention is, for example, a two-layer spiral coil having a structure in which conductors are provided in a spiral shape on the front and back surfaces of an insulating layer and each conductor is connected through a through hole. Further, a spiral coil having only one layer of spiral conductors may be used as long as there is no problem in taking out the terminal. Also,
In addition to spiral coils, meandering coils can also be used.

Although the planar inductor having the above-mentioned structure is a so-called outer iron type, the planar inductor according to the present invention is not limited thereto. For example, a so-called inner iron type planar inductor may be configured, which has a structure in which spiral coils are formed on both sides of a laminate of ferromagnetic layers.

Furthermore, when spiral coils are stacked, the inductance increases, but in this case, it is desirable that only an insulating layer be interposed between the spiral coils, and that no ferromagnetic layer be interposed. This is because interposing a ferromagnetic layer between the spiral coils hardly contributes to an increase in inductance, but rather increases the overall thickness of the planar inductor and lowers the performance per unit volume.

The insulating film is preferably one that can be electrically insulated and has a low dielectric constant close to 1, such as polyimide or SiO
2 etc. can be used. Also, its thickness is 1 μm
The above is practical. This is because when a capacitance component occurs between the coil and the magnetic material, the performance as an inductor deteriorates. However, if it is too thick, the performance per unit volume will deteriorate, so it is desirable that it be as thin as possible.

[0011] In the present invention, the plurality of ferromagnetic layers include F.
E-based amorphous alloys, Co-based amorphous alloys, etc. can be used, and the forming method is not particularly limited, and even if foils such as amorphous ribbons are used, known film forming methods such as sputtering and CVD can be used. A film separated by an insulating film using a method may also be used. At that time, it is desirable that the thickness of each layer is 100 μm or less. Generally, when a planar inductor is applied to a DC-DC converter and used in a frequency band of 10 kHz or higher, if the thickness of the ferromagnetic layer exceeds 100 μm, the magnetic flux will not penetrate inside the ferromagnetic layer due to the skin effect. This is because the inductance does not increase even though the thickness of the inductor increases, and the inductance per unit volume actually decreases, resulting in a decrease in the performance of the inductor. Further, when used for high frequencies, it is preferable that each ferromagnetic layer is separated by an insulating film such as SiO2.

In the present invention, by providing a plurality of ferromagnetic layers, good DC superimposition characteristics can be obtained even when a large DC current is superimposed. At this time, the magnetic path for the magnetic flux flowing in the ferromagnetic layer far from the coil is longer than the magnetic path for the magnetic flux flowing in the ferromagnetic layer near the coil, so if the thickness and permeability of both are If they are the same, the magnetic resistance of the latter will be smaller than the magnetic resistance of the former, and most of the magnetic flux will flow through the ferromagnetic layer closest to the coil, and the ferromagnetic layer farther from the coil will not be utilized effectively. , the inductance does not improve.

Therefore, when the plurality of ferromagnetic layers in the present invention are combined with a spiral coil to form a planar inductor, the magnetic anisotropy has a uniaxial magnetic easy axis in a direction perpendicular to the direction of magnetic flux, that is, in the circumferential direction. has been granted,
As the ferromagnetic layers move away from the spiral coil, the magnitude of the magnetic anisotropy imparted to each ferromagnetic layer gradually decreases. Here, the right angle in the right angle direction includes the vicinity of the right angle, and is effective if it has a component in the right angle direction. In other words, if the magnetic permeability of the ferromagnetic layer far from the coil is greater than that of the ferromagnetic layer closer to the coil, the magnetic resistance of the former will also be smaller, and magnetic flux will flow through both. Therefore, the overall magnetic resistance decreases, each layer is effectively utilized, and the inductance increases. On the other hand, the effective magnetic permeability μ is inversely proportional to the magnitude K of the magnetic anisotropy introduced in the direction perpendicular to the magnetic flux, so (μ=2πMs2 /K±δ, 4π
Ms: saturation magnetization), if you start with the ferromagnetic layer closest to the coil and decrease the K of the ferromagnetic layer as you move away from the coil, the μ of the ferromagnetic layer will gradually increase as you move away from the coil. , it is possible to improve the DC superimposition characteristics of the inductance and at the same time increase the value of the inductance itself. Further, in the present invention, the saturation magnetization 4πMs of the ferromagnetic layer is desirably large in order to obtain good DC superimposition characteristics, and is preferably 10 kG or more.

As a method for obtaining the above-mentioned magnetic anisotropy, for example, a hole is made in the center of the ferromagnetic layer, a conductive wire is passed through the hole, and a direct current is passed through the hole and heat treatment is performed in a magnetic field to provide the magnetic anisotropy. , a method of applying by laser patterning, etc., and a method of applying by introducing a plurality of magnetic gaps in the direction perpendicular to the magnetic flux into the ferromagnetic layer. In the case of laser patterning, for example, magnetic anisotropy is achieved by selectively irradiating a part of the ferromagnetic layer with a heating energy beam such as a laser to form regions that are not irradiated and regions that have different magnetic properties. All you have to do is give it. In addition, by imparting magnetic anisotropy with a uniaxial easy axis in the direction perpendicular to the magnetic flux to these ferromagnetic layers, the direct current superimposition characteristics can be improved, and at the same time, high frequency loss can be reduced because rotational magnetization is the main component. The high frequency characteristics are also improved.

[0015]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. Example 1

As shown in FIG. 1(A) and the AA' cross section in FIG. 1(B), first, a 25 μm thick polyimide film 3b was used as an insulating layer, and 100 μm thick Cu foil was pasted on both sides. Prepare a double-sided FPC board (flexible printed circuit board) connected through the through hole 4 in the center, and etch the Cu foil on both sides to make the outer circumference dimension 11 m.
m x 11mm, coil line width 200μm, coil pitch 2
A planar coil 1 was fabricated by processing spiral coils 2a and 2b having a diameter of 50 μm and a coil winding number of 40 times (20 times on each side).

On the other hand, Fe produced by the single roll method
It has a composition of 67Co18Si1 B14 and an average thickness of 1
A square foil with a side length of 15 mm is cut from a ferromagnetic amorphous alloy ribbon with a width of 6 μm and a width of 25 μm, and a YAG laser is used to pattern the surface (free surface) of the foil as shown in Figure 2(a). The laser beam with a beam diameter of 50 μm was changed to three pitches: 0.5 mm, 1 mm, and 2 mm, and the distance was 10 m.
/min. By irradiating at a scanning speed of did. The magnitude of magnetic anisotropy energy imparted to these three types of ferromagnetic foils is A: 1 x 104 erg/cc.
, B: 5×103 erg/cc, C: 2×103 e
It was rg/cc.

Next, a ferromagnetic foil is applied to both sides of the planar coil 1 through a 7 μm thick polyimide film used as the insulating layers 3a and 3c, starting from the side closest to the planar coil 1.
, B, and C were laminated in this order to form ferromagnetic layers 5a to 5f, thereby manufacturing a planar inductor. Comparative example 1

Three sheets of ferromagnetic foil A are laminated on both sides of the same spiral coil as used in Example 1 via a 7 μm thick polyimide film to form ferromagnetic layers 5a to 5f, and a planar inductor is formed. Created. Example 2

[0020] (Co0.
A planar inductor was produced in the same manner as in Example 1 except that an amorphous alloy having a composition of 8Fe0.2)78Si8B14, an average thickness of 16 μm, and a width of 25 mm was used for the ferromagnetic foil. In addition, three types of ferromagnetic foils A', B',
The magnitude of the magnetic anisotropy energy given to C' is A'
:4×103erg/cc, B':2×103erg
/cc, C': 1 x 103 erg/cc. Comparative example 2

A planar inductor was produced in the same manner as in Comparative Example 1 except that ferromagnetic foil A' was used instead of ferromagnetic foil A. Figure 3 shows the results of measuring the DC superposition characteristics of inductance L for the planar inductors fabricated in Example 1 and Comparative Example 1. Figure 4 shows the measurement results. As is clear from these figures, according to the present invention, the DC superimposition characteristics are improved without a decrease in L of the planar inductor.

[0022]

As described in detail below, according to the present invention, it is possible to provide a planar inductor with high inductance and excellent DC superimposition characteristics.

[Brief explanation of the drawing]

FIG. 1 (a) A plan view of a planar inductor according to an example, and (b) a sectional view taken along line AA' in (a).

FIG. 2 (a) A diagram showing a pattern of laser irradiation according to an example, and (b) a diagram showing the direction of magnetic anisotropy obtained by laser irradiation according to an example.

FIG. 3 is a diagram showing the characteristics of planar inductors manufactured in Example 1 and Comparative Example 1.

FIG. 4 is a diagram showing the characteristics of planar inductors manufactured in Example 2 and Comparative Example 2.

FIG. 5 is a diagram showing a conventional planar inductor.

[Explanation of symbols]

1... Planar coils 2a, 2b... Spiral coils 3a, 3b, 3c, 3d, 3e, 3f, 3g... Insulating layer 4
...Through holes 5a, 5b, 5c, 5d, 5e, 5f...Ferromagnetic layer 6a
, 6b...terminal

Claims (1)

[Claims] 1. A planar inductor in which a plurality of ferromagnetic layers are provided on both sides of a spiral coil with insulating layers interposed therebetween, wherein the ferromagnetic layer has magnetic anisotropy with a uniaxial magnetic easy axis in a direction perpendicular to the magnetic flux. and the magnitude of the magnetic anisotropy decreases as the distance from the spiral coil increases.