JP4281858B2 - Magnetic film - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic film, and more particularly to a magnetic film for absorbing unnecessary electromagnetic waves generated during operation of a communication device or the like.
[0002]
[Prior art]
With the recent deterioration of the electromagnetic environment, a high-performance electromagnetic wave absorbing material is desired. In addition, with the development of high frequency electronic equipment, high performance electromagnetic wave absorbing materials are also demanded in various magnetic device fields such as inductors, transformers and magnetic heads mounted on high frequency circuit boards.
[0003]
As such an electromagnetic wave absorbing material, a soft magnetic material having a high magnetic permeability can be used. This soft magnetic material has (1) a large saturation magnetization, (2) a small magnetocrystalline anisotropy constant K and magnetostriction λ, a small anisotropic dispersion, and (3) a high electric resistance. Characteristics are required.
[0004]
In order to obtain an electromagnetic wave absorbing material that satisfies these conditions, JP-A-8-250330, JP-A-10-270246, and JP-A-10-241938 propose magnetic films having a nanogranular structure. This is because the crystal grain size of the metal soft magnetic material is about 1 nm to 10 nm, and the particles are electrically insulated from each other, so that alumina (Al ₂ O _Three ) And silica (SiO ₂ ) Is deposited. As a result, the magnetic film achieves high magnetic permeability and high electrical resistance.
[0005]
However, these existing magnetic films with a nano-granular structure have a metal soft magnetic material as the main phase and a non-magnetic phase at the grain boundary, so the non-magnetic phase at the grain boundary has deteriorated the magnetic properties of the magnetic film. . Further, the electric resistance of this magnetic film is an order of magnitude higher than that of a normal metal soft magnetic material, but the electric resistance is basically low because the main phase is a metal soft magnetic material.
[0006]
In general, when a metal soft magnetic material having a low electric resistance is used in a high frequency band of 1 MHz or more, eddy current loss increases and its use becomes difficult. Therefore, when a magnetic film containing a conventional metal soft magnetic material is used in a high frequency band, for example, Si or Al is added to Fe, which is a soft magnetic material, For example, an amorphous magnetic material with high resistance was used. However, in the high frequency band, a desired electric resistance cannot be obtained, and instead of these magnetic materials, ferrite, which is a soft magnetic and high electric resistance oxide magnetic body, has been used exclusively. For example, the electrical resistivity of NiZn ferrite is 10 ^Ten Ω · cm, metal electrical resistivity is 10 ^-6 Considering that it is about Ω · cm, the electrical resistance is extremely large, and the occurrence of eddy current loss in the high frequency band is reduced.
[0007]
[Problems to be solved by the invention]
Incidentally, in recent years, mobile phones have exploded in popularity, and at the same time, there is a concern about local input of electromagnetic waves (Specific Absorption Rate, SAR) to the human body. Methods for preventing this have been proposed in Japanese Patent Application Laid-Open Nos. 2001-339496, 2001-352382 to 2001-352388, and in Japanese Patent Application Laid-Open No. 2001-320457. In this method, a sheet-like component in which a soft magnetic material is dispersed in a resin is arranged in the vicinity of a hot spot (point where SAR is maximized) of a mobile phone. Thereby, the magnetic field distribution in the vicinity of the hot spot is forcibly changed, and the penetration of the magnetic flux into the human body is suppressed. The soft magnetic material used for this is required to have a high magnetic permeability. Moreover, in order to lose energy by magnetic loss, a high magnetic permeability is required for the soft magnetic material. When ferrite is used for such a soft magnetic material, although electric resistance is high, there is a problem that it is difficult to achieve a desired magnetic permeability.
[0008]
In the high frequency circuit board, the CPU clock signal exceeds 2 GHz, and the noise accompanying this is a higher frequency. Conventionally, ferrite beads have been widely used to remove this noise. Ferrite beads have high impedance (mainly resistance components) in a high frequency band, and the generated noise is removed by heat conversion. However, in the high frequency band such as the GHz band, the impedance is insufficient, and noise cannot be sufficiently removed. Therefore, further increase in magnetic permeability of ferrite has been demanded.
[0009]
In the field of micro magnetic devices, there has been a demand for soft magnetic materials having high electrical resistance and high magnetic permeability, particularly in a high frequency band. From the viewpoint of high electrical resistance, ferrite is ideal because it is an oxide, but it has the disadvantage of low magnetic permeability compared to metallic materials.
[0010]
In the field of communications, higher frequencies are being developed for mobile phones (800 MHz, 900 MHz, 1.5 GHz, 2 GHz), Bluetooth (2.45 GHz), wireless LAN (5 GHz), GPS (1.5 GHz), and the like. In this band, if the impedance matching type radio wave absorber for preventing radio wave interference is formed of spinel ferrite, the magnetic permeability is lowered due to the limit of the snake. Therefore, there has been a drawback that the thickness of the impedance matching type radio wave absorber has to be made very thick.
[0011]
Hexagonal ferrite, which is said to exceed the snake limit, is disclosed in Japanese Patent No. 2717815 and Japanese Patent Application Laid-Open No. 9-110432. However, since the magnetic permeability is also low, the thickness of the radio wave absorber is accordingly reduced. Become thicker. Among hexagonal ferrites, the M-type ferrite disclosed in JP-A-10-162675, the IEICE General Conference, B-4-65, p350 (1998), and JP-A-11-354972 is a high-frequency ferrite. Application has been attempted as an impedance matching type electromagnetic wave absorber in a band, but the magnetic permeability is as low as about μ ″ = 5.
[0012]
The present invention has been made in view of these points, and an object of the present invention is to provide a magnetic film with high magnetic permeability and high electrical resistance that has high electromagnetic wave absorption ability even under a use environment in a high frequency band. To do.
[0013]
[Means for Solving the Problems]
According to the present invention, in the magnetic film having electromagnetic wave absorbing ability, the first magnetic phase composed of the crystal grains of the plurality of types of oxide magnetic materials and the plurality of types of oxidation around the first magnetic phase. And a second magnetic phase that is a grain boundary formed of a magnetic material. It has a nanogranular structure, and the composition ratio of the plurality of types of oxide magnetic materials in the first magnetic phase is equal to the composition ratio of the plurality of types of oxide magnetic materials in the second magnetic phase. A magnetic film is provided.
[0014]
In such a magnetic film, the first magnetic phase that is a crystal grain and the second magnetic phase that is the grain boundary both have a ferrite, for example. Multiple species It is made of an oxide magnetic material. That is, the phases constituting the magnetic film are all formed of an oxide magnetic material having a high electrical resistance. Thereby, compared with the case where a metal magnetic body is included conventionally, higher electrical resistance can be achieved, and high magnetic permeability can be obtained.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 2 is a schematic diagram of a magnetic film forming apparatus.
[0016]
For the formation of the magnetic film of the present invention, an aerosol deposition (AD) method is used in which the fine particle powder, which is a raw material of the magnetic film to be formed, is aerosolized and collides with a deposition object such as a substrate to form a thick film. . In this AD method, the raw material powder mixed at a ratio equal to the composition of the target magnetic film is aerosolized and sprayed onto the film formation object, thereby efficiently forming a magnetic film having a desired composition and film thickness. Can do.
[0017]
A magnetic film forming apparatus 10 for performing this AD method includes a mixer 11, a chamber 12, and a rotary pump 13.
The raw material powder 14 is charged into the mixer 11, and the raw material powder 14 charged therein is mixed by the vibration of the mixer 11. Thereby, the raw material powder 14 can be mixed uniformly and the deviation of the particle size distribution can be eliminated.
[0018]
Inside the chamber 12, a nozzle 15 connected to the mixer 11 is disposed, and the raw material powder 14 is aerosolized and injected from the tip of the nozzle 15. A substrate 20 on which a mask 16 is mounted is arranged on the tip side of the nozzle 15. When the raw material powder 14 is sprayed from the tip of the nozzle 15, the particles 14a of the raw material powder 14 are laminated on the surface of the substrate 20 to form a film.
[0019]
The rotary pump 13 is used for adjusting the pressure in the chamber 12. Here, the pressure in the chamber 12 is 10 ^-2 Set to Torr.
In addition, the magnetic film can be formed at a low temperature of room temperature to about 200 ° C. Further, after the magnetic film is formed on the substrate 20, a heat treatment is performed for the purpose of expressing an optimum structure by a conventional sputtering method. Absent.
[0020]
When forming a nano-granular magnetic film by the AD method, the powder constituting the crystal grain as the main phase and the grain boundary as the boundary between the crystal grains is charged into the mixer 11 as the raw material powder 14, and the aerosol is discharged from the nozzle 15. And sprayed onto the substrate 20.
[0021]
The composition ratio between the crystal grains and the grain boundaries of the magnetic film formed here substantially coincides with the mixing ratio of the raw material powder 14 charged in the mixer 11 before the magnetic film is formed. In contrast, in the conventional sputtering method, the composition of the magnetic film to be formed is the target used (Fe and Al ₂ O _Three It is necessary to determine the composition ratio based on the area ratio and the like, and to develop an optimum structure by heat treatment, and it is difficult to control the composition. In this regard, when the AD method is used for forming the magnetic film, the degree of freedom of the composition of the magnetic film that can be formed can be remarkably improved.
[0022]
Furthermore, according to the AD method, since no heat treatment is performed, the crystal structure of the raw material powder 14 is not changed by heat, and a magnetic film having a target crystal structure can be formed. Further, unlike the conventional sputtering method, a target is not required, so that the magnetic film can be formed at a low cost.
[0023]
Further, this AD method has a high film forming speed, and can adjust the spraying time of the raw material powder 14 to form a magnetic film with an arbitrary film thickness. Furthermore, the film can be well attached to the film formation object and can be firmly attached. Therefore, a magnetic film having an appropriate film thickness can be formed with a desired composition on the deposition objects (substrate, housing, parts, etc.) of various materials.
[0024]
Here, a method for forming the magnetic film will be described with a specific example.
First, as the raw material powder 14, Ni _0.5 Zn _0.5 Fe ₂ O _Four 70 g of powder (average particle size 200 nm), Mn _0.4 Zn _0.6 Fe ₂ O _Four 30 g of powder (average particle size 200 nm) is weighed and mixed so that the total amount becomes 100. And these raw material powders 14 are thrown into the mixer 11, and the mixer 11 and the raw material powders 14 are vibrated. The chamber 12 is driven by a rotary pump 13 to 10 ^-2 Depressurize to Torr. Next, SiO, which is the substrate 20 with the mask 16 mounted in the chamber 12. ₂ Set the board. Thereafter, when the nozzle 15 is opened at room temperature, the raw material powder 14 is aerosolized and injected from the nozzle 15 due to a pressure difference between the inside of the chamber 12 and the mixer 11. The film thickness of the magnetic film to be formed is adjusted by the jetting time at this time.
[0025]
FIG. 1 is a schematic diagram of a part of a magnetic film structure.
In the above AD method, Ni _0.5 Zn _0.5 Fe ₂ O _Four Powder and Mn _0.4 Zn _0.6 Fe ₂ O _Four The magnetic film 30 formed by using two kinds of powders has crystal grains having NiZn ferrite 31 and MnZn ferrite 32 as a first oxide magnetic body as a first magnetic phase. Furthermore, the magnetic film 30 has a thin grain boundary having the NiZn / MnZn ferrite 33 as the second oxide magnetic body as the second magnetic phase. Both the first magnetic phase and the second magnetic phase are formed of a ferrite material, and the magnetic film 30 has a nanogranular structure.
[0026]
In the formation of the magnetic film 30, the diameter of each crystal grain is about 1 nm to 50 nm, preferably about 2 nm to 20 nm, in order to develop soft magnetism. If the crystal grains are too small, they exhibit superparamagnetic behavior and soft magnetism decreases. If the crystal grains are too large, the properties as ferrite crystals become strong, which is not preferable. In order to achieve high permeability, the particles must be magnetically coupled by the nano-granular structure, and the crystal magnetic anisotropy must be small because it is a microcrystal, and the magnetic moment must not be reduced by thermal fluctuations. There is. Therefore, the crystal grain size of the magnetic film 30 is preferably about 2 nm to 20 nm.
[0027]
Note that the crystal grain size greatly depends on the particle size of the powder used as a raw material. Therefore, when the magnetic film 30 is formed, the crystal grain size can be controlled at the nano level as described above by controlling the grain size of the powder as a raw material.
[0028]
FIG. 3 and FIG. 4 show the result of the characteristic evaluation for the magnetic film 30. Here, the characteristics of the magnetic film 30 having a film thickness of 50 μm formed for 10 minutes at a film formation rate of about 5 μm / min were evaluated. At this time, the sample size was 5 mm × 8 mm.
[0029]
FIG. 3 is a diagram showing the measurement results of magnetic characteristics. In FIG. 3, the horizontal axis represents the magnetic field (Oe), and the vertical axis represents the magnitude of magnetization (kG).
The magnetic properties of the magnetic film 30 formed using the AD method were measured by a VSM (Vibrating sample magnetometer, BHV35) manufactured by Riken Denshi.
[0030]
As a result of the measurement, the saturation magnetization of the magnetic film 30 was 3.7 kG, and the coercive force was 0.01 Oe. The value of the saturation magnetization is equal to the value containing 67 vol% and 33 vol% of NiZn ferrite 31 and MnZn ferrite 32, respectively. Further, the value of the holding force is about one tenth of that of MnZn ferrite alone. Therefore, it can be said that the magnetic film 30 exhibits excellent soft magnetic characteristics.
[0031]
FIG. 4 is a diagram showing the results of permeability measurement. In FIG. 4, the horizontal axis represents frequency (GHz), and the vertical axis represents magnetic permeability (μ ′, μ ″).
The magnetic permeability of the magnetic film 30 was measured in a frequency band up to 3 GHz with a thin film magnetic permeability measuring device (PMF3000) manufactured by Ryowa Denshi.
[0032]
The maximum value of the magnetic permeability μ ″ exceeds 70 at a frequency of 4 GHz, and the maximum value of μ ′ also exceeds 70. It can be said that the magnetic film 30 exhibits excellent soft magnetic characteristics in a high frequency band.
[0033]
The electric resistance of the magnetic film 30 is about 10 ^Four Ω showed a very high value comparable to NiZn ferrite alone. Thus, it can be said that the magnetic film 30 whose crystal grains are NiZn ferrite 31 and MnZn ferrite 32 and whose grain boundary is NiZn / MnZn ferrite 33 is very excellent in high frequency characteristics.
[0034]
In the above example, the raw material powder 14 is Ni. _0.5 Zn _0.5 Fe ₂ O _Four Powder and Mn _0.4 Zn _0.6 Fe ₂ O _Four Although the case where two types of ferrite powders are used has been described, the magnetic film can also be formed by one type of ferrite powder.
[0035]
FIG. 5 is a schematic view of a magnetic film structure formed using NiZn ferrite powder.
The magnetic film 30a is formed in a nano-granular shape in which both crystal grains and their grain boundaries are NiZn ferrites 31a and 32a. Also in the magnetic film 30a, as described above, the crystal grain size is preferably about 1 nm to 50 nm and preferably about 2 nm to 20 nm. Even with such a configuration, good high-frequency characteristics are exhibited.
[0036]
As shown in the above example, the magnetic film has a nanogranular structure in which the first magnetic phase is a crystal grain of an oxide magnetic material and the second magnetic phase is a grain boundary of the oxide magnetic material. The oxide magnetic material for forming the first magnetic phase and the second magnetic phase is a high electrical resistance ferrite, and particularly has a high magnetic permeability in a high frequency band from MHz to GHz. Are preferably used. That is, it is desired that the magnetocrystalline anisotropy and magnetostriction are small and the saturation magnetization is high. As such a ferrite material, spinel magnetic oxide MeFe ₂ O _Four (Me is a divalent metal ion) or hexagonal magnetic oxide (BaFe ₁₂ O ₁₉ , SrFe ₁₂ O ₁₉ , Ba ₂ Me ₂ Fe _{twenty two} O _{twenty two} , BaMe ₂ Fe ₁₆ O ₂₇ Or Ba _Three Me ₂ Fe _{twenty four} O ₄₁ , Me is preferably a divalent metal ion).
[0037]
Where MeFe ₂ O _Four In addition to Me = Ni, Ni as shown in the above example _x Zn _1-x It is more preferable to use a composite and substituted spinel type ferrite as described above because the magnetic permeability increases.
[0038]
MeFe ₂ O _Four Is MeO · Fe ₂ O _Three It is a compound of metal oxide and iron oxide as represented by Fe ²⁺ In order to suppress the generation of ions, the composition was changed to MeO: Fe ₂ O _Three = 51: 49 or MeO: Fe ₂ O _Three = 52: 48 can also be controlled.
[0039]
As the hexagonal magnetic oxide, MeO.6Fe ₂ O _Three (Or MeFe ₁₂ O ₁₉ ) Type M ferrite (Me = Ba, Sr, Pb), Ba ₂ Me ₂ Fe ₁₂ O ₁₉ Y-type ferrite (Me = Mg) ²⁺ , Mn ²⁺ , Fe ²⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ , Zn ²⁺ ), BaMe ₂ Fe ₁₆ O ₂₇ W-type ferrite (Me = Mg) ²⁺ , Mn ²⁺ , Fe ²⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ , Zn ²⁺ ), And Ba _Three Me ₂ Fe _{twenty four} O ₄₁ Z-type ferrite (Me = Mg) ²⁺ , Mn ²⁺ , Fe ²⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ , Zn ²⁺ ) Etc. can be used.
[0040]
Among these, Ba, Z, and Y type ferrites are Ba. ²⁺ Sr instead of ions ²⁺ Even if ions are used, they have the same crystal structure and substantially the same magnetic characteristics. Further, regarding M and W type ferrite, as disclosed in JP-A-11-354972, Fe ³⁺ Ions, for example Ti ⁴⁺ Mn ²⁺ Or Zr ⁴⁺ Zn ²⁺ By performing the composite replacement as described above, it is possible to change the resonance frequency and suppress the decrease in the permeability in the high frequency band. Furthermore, in order to obtain a desired frequency characteristic by changing the resonance frequency, as a raw material powder, BaFe _Ten Sn _1.5 Ni _0.5 O ₁₉ A hexagonal ferrite having a composition can also be used.
[0041]
One or two or more of these ferrite materials are selected, and a magnetic film in which both crystal grains and grain boundaries are composed of ferrite can be formed by an AD method using the powder. That is, even a magnetic film having a grain boundary in a state where a plurality of types of ferrite crystal grains or a plurality of types of ferrite are mixed can be formed.
[0042]
Examples of applying the magnetic film to various applications will be described below.
The film thickness of the magnetic film varies slightly depending on the application. In the case of chip beads, the component size is a so-called 1608 (1.6 mm × 0.8 mm × 0.8 mm) type, 1005 (1.0 mm × 0.00 mm). 5mm × 0.5mm) type and 0603 (0.6mm × 0.3mm × 0, 3mm) have been miniaturized, and it is preferable to form a magnetic film with a film thickness that matches the standard of the product. In recent years, a material having a film thickness of 500 μm or less has been increasingly used, and the magnetic film of the present invention has a thinner film thickness and exhibits excellent high frequency characteristics.
[0043]
In addition, when the inductor and the transformer are used as a micro magnetic device, a film thickness of several μm is preferable.
Thus, by using the magnetic film of the present invention, beads, inductors and transformers can be formed in a small size with good high frequency characteristics.
[0044]
Next, the case where it uses as an impedance matching type electromagnetic wave absorber is described. In this case, for example, a high magnetic permeability μ ′, μ ″ as shown in FIG. 4 of about 70 at the maximum can be expressed, so that the impedance matching type electromagnetic wave absorber can be thinned.
[0045]
6A and 6B are diagrams showing thickness design curves of the impedance matching type electromagnetic wave absorber, wherein FIG. 6A shows a case where the thickness is 150 μm, and FIG. 6B shows a case where the thickness is 200 μm. In FIG. 6, the horizontal axis represents frequency (GHz) and the vertical axis represents magnetic permeability (μ ′, μ ″).
[0046]
6 (a) and 6 (b), for example, μ = 30−45j can be obtained at 5 GHz, and the impedance matching type radio wave absorber can be formed with a thickness of about 150 μm to 200 μm. Therefore, it is possible to form an impedance matching type radio wave absorber having a thinner thickness than the conventional one.
[0047]
Next, the case where it uses for an electronic device housing | casing is described. The electronic device casing has a thickness of about 1 mm if it is a normal plastic molded product, and is about 0.5 mm in the thinnest part. A magnetic film is formed on the inner surface of such a case to suppress electromagnetic interference. At this time, it is desirable to make the sum of the thickness of the plastic molded product and the thickness of the magnetic film as thin as possible from the viewpoint of securing the component arrangement space inside the housing or miniaturizing the electronic device.
[0048]
In the case of the electromagnetic wave absorbing sheet normally used inside the casing, the thickness (d) is about 0.5 mm, and μ ″ = 5. Here, the electromagnetic wave absorption characteristic (electromagnetic wave absorption energy) is simplified. Therefore, if evaluated by μ ″ × d, in the case of the electromagnetic wave absorbing sheet, μ ″ × d = 2.5. On the other hand, in the magnetic film of the present invention, it is possible to express about μ ″ = 50. In this case, even if the thickness d formed on the inner surface of the casing is reduced to about 50 μm, which is one tenth of the electromagnetic wave absorbing sheet, μ ″ × d = 2.5 and there is no performance degradation. A magnetic film can be thinly formed on the surface, so that a space for arranging components can be secured and the electronic device can be downsized.
[0049]
Next, the case where it uses for a high frequency circuit board is described. In the high frequency circuit board, the magnetic film of the present invention can be used in order to suppress the generation of common mode noise, which is a source of high frequency noise, among normal mode noise and common mode noise.
[0050]
FIG. 7 is a schematic cross-sectional view of a high-frequency circuit board.
The high-frequency circuit board 40 includes glass epoxy substrates 42a, 42b, and 42c on which wiring layers 41a, 41b, and 41c are formed, respectively, and a power supply layer 45 and a ground that sandwich the magnetic film 44 between the glass epoxy substrates 42b and 42c. Layer 46 is formed. Each wiring layer 41a, 41b, 41c is electrically connected by a plurality of via holes 43 formed in the glass epoxy substrates 42a, 42b, 42c and the magnetic film 44. Electronic components 47 such as ICs and various devices are mounted on the wiring layers 41a and 41c.
[0051]
In the high-frequency circuit board 40, the magnetic film 44 is used as one of the layers constituting the same. Since the magnetic film 44 has a frequency dependence of magnetic permeability and μ ″ increases in the MHz to GHz band, the magnetic film 44 is formed between the power supply layer 45 and the ground layer 46 of the high-frequency circuit board 40. Therefore, the common mode noise that passes through the ground layer 46 can be effectively reduced.
[0052]
Usually, the thickness of the high-frequency circuit board 40 is 50 μm to 70 μm, and the magnetic film 44 can be easily formed as a single layer constituting this. Therefore, unnecessary anti-radiation components such as those conventionally used are not required.
[0053]
Here, the structure in which the magnetic film 44 is formed between the power supply layer 45 and the ground layer 46 is shown. A film 44 can also be formed. As a result, noise generated in the electronic component 47 can be prevented from coupling to the wiring layers 41a and 41c.
[0054]
Next, the case where it uses as a SAR suppression body of a mobile telephone is described.
8A and 8B are diagrams for explaining a SAR suppression method in a mobile phone. FIG. 8A shows a case where a magnetic film is formed on the holder, FIG. 8B shows a case where a magnetic film is formed on the high-frequency block shield part, and FIG. It is a side view of a mobile phone when a magnetic film is formed on a substrate.
[0055]
The mobile phone 50 includes a housing 51, a display panel 52 attached to the operation surface side of the mobile phone 50, and a key operation unit 53, and a holder 54 is provided on the back side of the display panel 52. A main board 55 is disposed inside the casing 51, and electronic components 56 such as ICs and various devices are mounted thereon. Furthermore, a speaker 57 and a microphone 58 are provided on the operation surface side. Further, a battery 59 and a high-frequency block shield part 60 are provided on the back side of the mobile phone 50, and an antenna 61 is provided on the mobile phone 50.
[0056]
In such a cellular phone 50, a magnetic film is formed on the surface of the holder 54 as shown in FIG. 8A, or on the surface of the high-frequency block shield part 60 as shown in FIG. 8B. Or can be formed. Further, as shown in FIG. 8C, it can be formed for a specific electronic component 56 mounted on the main board 55. Further, it is possible to suppress SAR by forming a magnetic film on the inner surface of the casing 51 of the mobile phone 50.
[0057]
Thus, by forming a magnetic film inside the mobile phone 50, electromagnetic waves radiated from the mobile phone 50 are reduced, and intrusion of electromagnetic waves from the outside is also suppressed. Therefore, SAR can be suppressed without taking up space.
[0058]
【The invention's effect】
As described above, in the present invention, the first magnetic phase that is the crystal grains of the magnetic film and the second magnetic phase that is the grain boundary are both formed of an oxide magnetic material. By forming the magnetic film from an oxide magnetic material having a high electric resistance, a magnetic film having high magnetic permeability and good high frequency characteristics can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a part of a magnetic film structure.
FIG. 2 is a schematic diagram of a magnetic film forming apparatus.
FIG. 3 is a diagram showing the measurement results of magnetic characteristics.
FIG. 4 is a diagram showing the results of magnetic permeability measurement.
FIG. 5 is a schematic diagram of a magnetic film structure formed using NiZn ferrite powder.
6A and 6B are diagrams showing thickness design curves of an impedance matching type electromagnetic wave absorber, wherein FIG. 6A shows a case where the thickness is 150 μm and FIG. 6B shows a case where the thickness is 200 μm.
FIG. 7 is a schematic cross-sectional view of a high-frequency circuit board.
8A and 8B are diagrams for explaining a SAR suppression method in a mobile phone, in which FIG. 8A shows a case where a magnetic film is formed on a holder, FIG. 8B shows a case where a magnetic film is formed on a high-frequency block shield part, and FIG. FIG. 3 is a side view of a mobile phone when a magnetic film is formed on a substrate.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Magnetic film formation apparatus, 11 ... Mixer, 12 ... Chamber, 13 ... Rotary pump, 14 ... Raw material powder, 14a ... Particle, 15 ... Nozzle, 16 ... Mask, 20 ... Substrate, 30, 30a... Magnetic film, 31, 31a, 32a... NiZn ferrite, 32... MnZn ferrite, 33... NiZn / MnZn ferrite, 40. , 42b, 42c... Glass epoxy substrate, 43 .. via hole, 44 .. magnetic film, 45... Power layer, 46 .. ground layer, 47 .. electronic component, 50. 52 …… Display panel, 53 …… Key operation unit, 54 …… Holder, 55 …… Main board, 56 …… Electronic components, 57 …… Speaker, 58 …… Microphone, 59 …… Battery , 60 ...... high frequency block shield portion, 61 ...... antenna.

Claims (9)

In the magnetic film having electromagnetic wave absorbing ability,
A first magnetic phase comprising crystal grains of a plurality of types of oxide magnetic materials;
A second magnetic phase that is a grain boundary formed of the plurality of types of oxide magnetic bodies around the first magnetic phase;
Having a nano-granular structure consisting of
A magnetic film , wherein a composition ratio of the plurality of types of oxide magnetic materials in the first magnetic phase is equal to a composition ratio of the plurality of types of oxide magnetic materials in the second magnetic phase .   2. The magnetic film according to claim 1, wherein the plurality of kinds of oxide magnetic bodies include ferrite having a crystal structure of spinel type or hexagonal type.   2. The magnetic film according to claim 1, wherein the first magnetic phase has a crystal grain diameter of 1 nm to 50 nm. A first magnetic phase composed of crystal grains of a plurality of types of oxide magnetic materials, and a second magnetism that is a grain boundary formed by the plurality of types of oxide magnetic materials around the first magnetic phase. And a composition ratio of the plurality of types of oxide magnetic materials in the first magnetic phase and a composition ratio of the plurality of types of oxide magnetic materials in the second magnetic phase. Chip beads characterized by using equal magnetic films. A first magnetic phase composed of crystal grains of a plurality of types of oxide magnetic materials, and a second magnetism that is a grain boundary formed by the plurality of types of oxide magnetic materials around the first magnetic phase. And a composition ratio of the plurality of types of oxide magnetic materials in the first magnetic phase and a composition ratio of the plurality of types of oxide magnetic materials in the second magnetic phase. An inductor using equal magnetic films. A first magnetic phase composed of crystal grains of a plurality of types of oxide magnetic materials, and a second magnetism that is a grain boundary formed by the plurality of types of oxide magnetic materials around the first magnetic phase. And a composition ratio of the plurality of types of oxide magnetic materials in the first magnetic phase and a composition ratio of the plurality of types of oxide magnetic materials in the second magnetic phase. An impedance matching type electromagnetic wave absorber using equal magnetic films. A first magnetic phase composed of crystal grains of a plurality of types of oxide magnetic materials, and a second magnetism that is a grain boundary formed by the plurality of types of oxide magnetic materials around the first magnetic phase. And a composition ratio of the plurality of types of oxide magnetic materials in the first magnetic phase and a composition ratio of the plurality of types of oxide magnetic materials in the second magnetic phase. An electronic device casing using an equal magnetic film for all or a part thereof. A first magnetic phase composed of crystal grains of a plurality of types of oxide magnetic materials, and a second magnetism that is a grain boundary formed by the plurality of types of oxide magnetic materials around the first magnetic phase. And a composition ratio of the plurality of types of oxide magnetic materials in the first magnetic phase and a composition ratio of the plurality of types of oxide magnetic materials in the second magnetic phase. A high-frequency circuit board using an equal magnetic film as a part thereof. A first magnetic phase composed of crystal grains of a plurality of types of oxide magnetic materials, and a second magnetism that is a grain boundary formed by the plurality of types of oxide magnetic materials around the first magnetic phase. And a composition ratio of the plurality of types of oxide magnetic materials in the first magnetic phase and a composition ratio of the plurality of types of oxide magnetic materials in the second magnetic phase. An SAR suppressor using equal magnetic films.

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