JP2004103623A - Inductor and power supply using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inductor having a thickness of 1 mm or less and a low height and to provide a small-sized power supply which deals with a portable communication apparatus, etc. by using the same. <P>SOLUTION: A flat shape helical coil 4 made of a flat type conductor is disposed on a periphery of a core 3 obtained by forming a magnetic layer by sputtering on a thin substrate having a thickness of 10-25 μm, and a thin substrate with the magnetic layers formed on upper and lower surfaces of the coil 4 is disposed as a magnetic shielding layer. Thus, the inductor having the low height and a thickness of 1 mm or less is obtained. The small-sized power supply can be obtained by using this inductor having the low height. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a low-profile inductor and a power supply mounted in a portable electronic device typified by a mobile phone, a notebook computer, or the like, and reduced in size by using the low-profile inductor.
[0002]
[Prior art]
2. Description of the Related Art Portable electronic devices are rapidly spreading due to the progress of multimedia by transmitting and receiving digital data and the expansion and enhancement of software used. In these portable electronic devices, a large number of devices are built in to operate various functions, and the power supply voltage required for each electronic circuit and LSI is various.
[0003]
Normally, a DC-DC converter and a linear regulator are used for this voltage conversion. DC-DC converters are composed of semiconductor elements such as semiconductor switches, rectifier diodes, and control ICs, magnetic elements such as inductors and transformers, and components such as capacitors. The mounting area is being reduced due to integration and the like.
[0004]
Along with this, downsizing is required for transformers and inductors that have conventional magnetic cores and windings. Conventionally, regulators that are advantageous in terms of downsizing have been used for these applications. There is a growing market demand for DC-DC converters that are compatible with lowering the LSI voltage and saving energy due to power savings and advanced functions.
[0005]
Against this background, among the components that make up a DC-DC converter, to reduce the height of components that use magnetism, such as tall and bulky inductors, the use of thin film manufacturing technology and the like A method of manufacturing a thin-film inductor composed of a coil and a planar coil has been studied, and a small power supply, that is, a micro power supply, which combines the methods, has been actively developed.
[0006]
Here, conventionally, inductors used for power supplies are roughly classified as follows from the viewpoint of a manufacturing method. (1) A ferrite inductor in which a coil is wound around a ferrite sintered body, (2) a laminated type inductor obtained by laminating a ferrite paste and a conductor paste and then firing, and (3) a winding coil is embedded in the ferrite paste. There are known coil-containing sintered inductors and (4) thin-film spiral inductors formed in all thin-film processes.
[0007]
The ferrite inductor is formed by winding a coil around a ferrite sintered body having a thickness of about 1 mm to form an inductor. With this feature, a high inductance value of 10 μH or more and a good superimposition characteristic can be obtained, and it has been used as a practical material so far. The drawback is that the dimensions are as large as 3-4 mm × 3-4 mm × 1-2 mm, and the thickness and area are too large for a micro power supply inductor.
[0008]
A factor that makes it difficult to reduce the height or thickness of the ferrite inductor is that the saturation magnetization is low. This is because a material having a low saturation magnetization needs to secure a certain volume or more in order to obtain sufficient characteristics. Another factor that makes it difficult to reduce the height is the brittleness of ferrite, and these factors limit the reduction in the height of ferrite inductors.
[0009]
In the laminated inductor, a ferrite paste and a silver paste for a conductor are alternately laminated, and after drying is completed, the inductor is cut and sintered at a low temperature to form an inductor structure. However, since the conductor is sintered at a low temperature, when a large current for a power supply is supplied, there is a large amount of heat generation, which causes problems such as a problem in withstand voltage and a reduction in height.
[0010]
Coil-containing sintered inductors are those that place the winding coil in ferrite paste and sinter at low temperature, cover the coil surface with an insulator, and use silver with high oxidation resistance for the coil conductor material. Generally, the winding coil is wrapped in ferrite, so it is difficult to reduce the height.
[0011]
The thin film inductor uses a film forming technique such as sputtering, and various inductors such as a spiral structure and a helical structure have been developed. However, there is a problem that the inductance value and efficiency are low. Furthermore, since the thin-film inductor is formed on a substrate, the substrate needs to have a certain thickness or more, and there is a problem that the reduction in height is limited due to the thickness of the substrate as a whole.
[0012]
In order to obtain a thin or low-profile inductor, it is necessary to use a thin magnetic material for the magnetic core. As one method for obtaining a thin magnetic body, there is a ribbon obtained by rapidly cooling a molten metal of a magnetic alloy. However, this also has a problem that the specific resistance of the whole ribbon is small, and the loss is large in a frequency band of several MHz due to high magnetic permeability.
[0013]
[Problems to be solved by the invention]
As described above, various inductors have been put to practical use, but none of them has been sufficiently adapted to a reduction in height for use in a micro power supply. Therefore, a technical problem of the present invention is to produce a low-profile inductor which cannot be obtained by a conventional method, and to construct a particularly small-sized, that is, a micro-power supply using a power supply using the same. And
[0014]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present invention has been made as a result of reexamining the film forming method, the structure, and the like, focusing on a thin film inductor among conventional inductors.
[0015]
That is, the present invention provides a magnetic core formed by laminating one or more substrates on which a magnetic layer is formed, a helical coil formed around the magnetic core, and a vertical position with respect to the magnetic core; An inductor, comprising a substrate provided with a magnetic layer formed outside the coil.
[0016]
Further, the present invention is the above-mentioned inductor, wherein the thickness is 1 mm or less.
[0017]
Further, the present invention is a power supply characterized in that the step-down or step-up power supply circuit using the inductor, the control IC, the capacitor, and the resistor is formed on a thin substrate.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
A magnetic material that is obtained in a thin film and has high magnetic permeability is suitable for the magnetic core of a low-profile inductor. In general, a thin film magnetic material obtained by rf sputtering in vacuum is suitable for such an application. The problem here is that such a thin-film magnetic material cannot be present only with a thin-film magnetic material because it is formed on a substrate.
[0019]
Therefore, in order to make the magnetic core itself thin, it is necessary to form a magnetic layer on a thin substrate. However, if the film is formed on a substrate having a thickness of about 10 to 25 μm, warpage occurs, and It was impossible to obtain a thin-film magnetic material in a specific manner. In the present invention, this problem has been solved by uniformly forming the magnetic layers on both surfaces of the substrate. Specifically, for example, a magnetic layer is formed on both surfaces of a film having a thickness of 10 to 25 μm, which is made of a polymer material having excellent heat resistance such as polyimide, and the substrate is cut and processed. A flat and thin magnetic core can be obtained.
[0020]
Then, by performing winding processing using a rectangular conductor, a low-profile inductor can be formed. Further, by disposing the thin magnetic core as a shielding layer on both sides of the obtained low-profile inductor, it is possible to prevent the magnetic flux from leaking to the outside, and to suppress the influence of the magnetic flux on peripheral devices. it can.
[0021]
With such a structure, the thickness of the entire low-profile inductor can be easily reduced to 1 mm or less. Furthermore, a low-profile micro power source can be obtained by arranging the low-profile inductor and other necessary components on a thin substrate.
[0022]
In the present invention, in order to obtain a thin magnetic core, a magnetic layer having a thickness of several μm is formed on a substrate having a thickness of about 10 to 25 μm. For film formation, sputtering or the like can be used. In this case, by forming the magnetic layers on both surfaces with a uniform thickness, even if a polyimide film is used for the substrate, the film can be formed without warping. In forming the magnetic layer, it is necessary to take measures such as cooling so that the heat of the plasma does not affect the substrate and the magnetic layer.
[0023]
As the magnetic layer, for example, an amorphous alloy exhibiting high magnetic permeability and a magnetic material providing a high saturation magnetization thin film are formed in a multilayer film to form a thin magnetic core having a low coercive force and corresponding to a high frequency band. It is also possible. In such a thin magnetic core having a multilayer structure, the magnetic layers are separated from each other by the substrate, there is no interaction between the magnetic layers, and it is easy to optimize the magnetic characteristics as the magnetic core of the low-profile inductor.
[0024]
As the substrate material, various substrate materials can be used in addition to the above-mentioned polyimide, and there is no particular limitation as long as it can be obtained in a thin plate shape, such as a glass fiber reinforced plastic substrate or polycarbonate. Further, as long as the material has flexibility, a film can be formed using a continuous film forming apparatus or the like. The above-mentioned materials generally have lower thermal conductivity than metals, but by using the above-mentioned magnetic materials, the magnetic layer functions as a heat sink and a magnetic core with a small rise in temperature can be formed.
[0025]
Next, a flat conductor is wound around the thin magnetic core to form a flat helical coil. After the helical coil is formed, a laminated body of a substrate and a magnetic thin film having the same configuration as the magnetic core is disposed on the upper and lower surfaces of the coil to prevent magnetic flux leakage from the helical coil.
[0026]
A low-profile inductor used for a micro power supply is required to be small and thin, and have a required inductance value and superimposed characteristics. In the thin magnetic core according to the present invention, in-plane magnetization is induced by the magnetic field generated from the helical coil, and the original magnetic permeability is exhibited in a magnetic field range where the magnetic flux density of the thin magnetic core is not saturated, that is, in a driving current range of the helical coil. , Inductance is obtained.
[0027]
In general, in the case of a low-profile type inductor, when the thickness of the magnetic core is reduced, in a magnetic material having a small saturation magnetization, the magnetic core tends to saturate in a low magnetic field region, and the superimposition characteristics tend to deteriorate. For example, in a single-layer core made of ferrite, quenched ribbon, etc., when the high-frequency magnetic flux penetrates the core, the effective thickness of the core becomes thin due to the skin depth, which tends to cause a decrease in inductance. No superimposition characteristics can be obtained.
[0028]
In the magnetic core used in the low-profile inductor according to the present invention, a composite multilayer structure can be obtained by forming a rectangular thin-film magnetic body elongated in the direction of the hard axis on a thin substrate and laminating it. In addition, since the magnetic shielding layers are arranged above and below the helical coil, the magnetic core is less affected by an external magnetic field and is not easily saturated. Therefore, the low-profile microinductor of the composite multilayer structure according to the present invention has excellent superimposition characteristics. Further, by using this, a micro power supply having excellent characteristics can be provided.
[0029]
【Example】
Next, specific examples will be described with reference to the drawings.
[0030]
(Example 1)
A Co-Fe-Si-B amorphous magnetic film having a thickness of 5 m was formed on both surfaces of a polyimide film having a thickness of 25 m. This was cut into a rectangle having a width of 3 mm and a length of 4 mm, and four pieces were laminated to form a magnetic core. Here, the layers are cut and then laminated, but four layers may be formed by bending.
[0031]
Next, a 25-turn winding was applied to the magnetic core using a rectangular conductor having a width of 100 μm and a thickness of 35 μm to form a helical coil. Here, the coil is wound directly on the magnetic core, but a coil whose dimensions when crushed are set so that the magnetic core used in this embodiment can be inserted may be separately prepared, and this may be crushed flat.
[0032]
Next, the polyimide film having a magnetic film having a thickness of 5 μm formed on both surfaces was cut into a width of 3.1 mm and a length of 4.2 mm, and each of the polyimide films was disposed above and below as a shielding layer. The above-mentioned polyimide film was attached as a substrate, and a through-hole for connecting to a circuit was formed at the end of the winding using paste solder to obtain a low-profile inductor having a thickness of 310 μm.
[0033]
FIG. 1 is a view showing a state where the upper shielding layer of the low-profile inductor 1 is removed. In FIG. 1, 2 is a substrate (polyimide film), 3 is a magnetic core, 4 is a helical coil, and 5 is a through hole.
[0034]
As a result of evaluating the characteristics of this inductor, good inductor characteristics were obtained in which the inductance value in the frequency range of 1 MHz to 10 MHz was 4 μH and the DC resistance: R _DC was 1Ω or less. This characteristic is a sufficient value for use in a control IC driven at a switching frequency of 3 MHz of a step-down micro power supply.
[0035]
FIG. 2 is a schematic diagram showing an example in which necessary components are arranged on the low-profile inductor 1 to constitute a micro power supply. In the micro power supply shown in FIG. 2, a control IC 6 is mounted on a bare chip, a 0603 series ceramic capacitor is used for the capacitor 8, a low-profile inductor according to the present invention is used, and a thin film resistor is used for the resistor 7. Was.
[0036]
Electrodes and the like were provided thereon, packaged using polyimide, and a micro power supply having an overall thickness of 0.9 mm, a length of 5 mm, and a width of 4 mm was obtained. Here, polyimide is used for packaging, but it is not limited to this as long as it is a polymer compound having a certain heat resistance.
[0037]
In the micro power supply shown in this example, when the input voltage was 4 V and the current was 200 mA, the efficiency was 80% or more when the output voltage was 1.8 V. The efficiency was 75% or more at an output voltage of 1.5 V, the efficiency was 70% or more at an output voltage of 1.2 V, and the efficiency was 60% or more at an output voltage of 0.9 V.
[0038]
(Example 2)
In the same manner as in Example 1, a magnetic film having a thickness of 5 μm was formed on both surfaces of a polyimide film having a thickness of 25 μm, cut into a rectangle having a width of 3 mm and a length of 4 mm, and two sheets were laminated to form a magnetic core. Thereafter, winding was performed for 25 turns in the same manner as in Example 1 to obtain a low-profile inductor.
[0039]
This inductor was evaluated for properties, the inductance value in the frequency band of 1MHz~10MHz _is, 2μH, _{R DC} is the result that less 1Ω was obtained. Since the switching frequency of the step-down type micro power supply is driven at 3 MHz, this inductance value was sufficient for use as a micro power supply.
[0040]
Next, the micro power supply shown in FIG. 2 was constructed using the inductor in the same manner as in the first embodiment. The configuration of the micro power supply shown in FIG. 2 is exactly the same as that of the first embodiment except for the low-profile inductor.
[0041]
In the micro power supply shown in this example, when the input voltage was 4 V and the current was 200 mA, the efficiency was 80% or more when the output voltage was 1.8 V. The efficiency was 75% or more at an output voltage of 1.5 V, the efficiency was 70% or more at an output voltage of 1.2 V, and the efficiency was 60% or more at an output voltage of 0.9 V.
[0042]
In the embodiment shown here, two or four polyimide films each having a magnetic layer formed on both sides were used as a magnetic core, however, even in the case of other numbers, a low-profile inductor and a Can be obtained.
[0043]
【The invention's effect】
As described above, according to the present invention, a magnetic layer is formed and patterned on a substrate made of a polyimide film or the like, a helical coil is formed by winding, and the magnetic layer is formed on the upper and lower surfaces of the helical coil by the same method. By arranging the substrate on which is formed as a shielding layer, it is possible to obtain a low-profile inductor that does not leak magnetic flux to the outside.
[0044]
Therefore, the low-profile inductor according to the present invention has a good inductance value and a superimposed characteristic even in a high frequency band, and is excellent as a low-profile inductor for a micro power supply. By using this, a micro power supply can be provided.
[Brief description of the drawings]
FIG. 1 is a view showing a state in which an upper shielding layer is removed from a low-profile inductor.
FIG. 2 is a schematic diagram illustrating an example in which a micro power source is configured.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Low profile inductor 2 Substrate 3 Magnetic core 4 Helical coil 5 Through hole 6 Control IC
7 resistor 8 capacitor

Claims (3)

A magnetic core formed by laminating one or more substrates on which a magnetic layer is formed; a helical coil formed around the magnetic core; An inductor comprising a substrate on which a magnetic layer is formed. The inductor according to claim 1, wherein the thickness is 1 mm or less. A power supply, wherein the step-down or step-up power supply circuit using the inductor, the control IC, the capacitor, and the resistor according to claim 1 or 2 is formed on a thin substrate.

Images