JPH07249888A - Electromagnetic wave absorption sheet - Google Patents

Abstract

PURPOSE:To effectively cope with an unnecessary electromagnetic wave of several hundreds of MHz or more by forming of one layer alloy magnetic material, and providing uniaxial magnetic anisotropy in a direction parallel to a film surface of the material. CONSTITUTION:An electromagnetic wave absorption sheet 1 is formed of one layer alloy magnetic material 2, and a sheet board 4 made of a nonmagnetic insulator is arranged to be held at a lower part of the material 2. An external magnetic field is applied toward a film surface of the material 2 at the time of manufacturing, and uniaxial magnetic anisotropy 5 is imparted to the surface. Thus, unnecessary electromagnetic wave of several hundreds of MHz can be coped with, and its manufacture can be facilitated.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an electromagnetic wave absorbing sheet.

[0002]

2. Description of the Related Art In recent years, with the spread of high-speed digital equipment,
The phenomenon that unwanted electromagnetic waves generated from these devices interfere with other devices (electromagnetic environment problem, EMC problem) has been taken up as new pollution. For example, unnecessary electromagnetic waves of 30 to 1000 MHz generated due to a common mode noise current superposed on a cable of a digital communication device have been regarded as a problem to be a disturbing wave to a television or the like. 30 above
An Mn-Zn ferrite plate has been conventionally used as an electromagnetic wave absorber for unwanted electromagnetic waves of up to 1000 MHz, and it is used by being attached to a cabinet of a communication device or the like. The electromagnetic wave absorber uses the property of magnetic loss of a magnetic material, and as a magnetic material, the relative magnetic permeability (μ _r = μ _r ′ −j
μ _r ″) is high, and resistance (μ _r ″> μ _r ′) is required. FIG. 10 shows frequency characteristics of relative permeability in Mn-Zn ferrite. Μ _r ″ ＞ several MHz or more
Although μ _r ′ is satisfied, the absolute value of μ _r is small, so
In order to obtain a large electromagnetic wave absorption effect, it was necessary to use a large amount of Mn-Zn ferrite plates. Further, as seen in FIG. 10, since the relative magnetic permeability of Mn-Zn ferrite has a very small value in the high frequency band, the effect as an electromagnetic wave absorber is drastically reduced at several hundred MHz or more. That is, the conventional electromagnetic wave absorber has a large volume, a heavy weight, and several hundred M
There was a drawback that it was not effective above Hz.

[0003]

SUMMARY OF THE INVENTION The present invention has been proposed in order to improve the above-mentioned drawbacks, and its purpose is to increase the volume and weight of conventional electromagnetic wave absorbers by several hundred MH.
It is intended to provide a sheet-like electromagnetic wave absorber that is small and lightweight, and that is effective against unnecessary electromagnetic waves of several hundred MHz or more, which solves the problem that it is not effective at z or more.

[0004]

[Means for Solving the Problems]

(1) In order to achieve the above object, the present invention comprises a single-layer alloy magnetic body, wherein the alloy magnetic body has a uniaxial magnetic anisotropy in a direction parallel to the film surface of the alloy magnetic body. The gist of the invention is an electromagnetic wave absorbing sheet characterized by having: (2) Further, the present invention comprises an alloy-based magnetic body bonded to a non-magnetic insulating sheet substrate, and the alloy-based magnetic body has a uniaxial magnetic anisotropy in a direction parallel to the film surface of the alloy-based magnetic body. Characterized in that a plurality of electromagnetic wave absorbing sheets having the above are laminated, and the directions of the uniaxial magnetic anisotropy of the alloy-based magnetic body in the respective electromagnetic wave absorbing sheets deviate from each other at a desired angle. The electromagnetic wave absorbing sheet is defined as the gist of the invention. (3) Further, the present invention comprises a multilayer body in which an alloy magnetic body and a non-magnetic insulator are alternately laminated, and the alloy magnetic body is arranged in a direction parallel to the film surface of the alloy magnetic body. The gist of the invention is an electromagnetic wave absorbing sheet having uniaxial magnetic anisotropy. (4) The electromagnetic wave absorbing sheet according to (3), wherein the uniaxial magnetic anisotropy directions of the alloy-based magnetic body are displaced from each other at a desired angle. (5) Further, in the present invention, the first alloy-based magnetic material is deposited on the substrate, then the non-magnetic insulator is formed thereon, and then the second alloy-based magnetic material is deposited on the non-magnetic insulator. SUMMARY OF THE INVENTION An electromagnetic wave absorbing sheet, wherein at least three or more multi-layered sheets are stacked, wherein each of the alloy-based magnetic bodies has uniaxial magnetic anisotropy in a direction parallel to the film surface. It is a thing. (6) The electromagnetic wave absorbing sheet as described in (5), wherein the directions of the uniaxial magnetic anisotropy of the respective alloy-based magnetic bodies are displaced at a desired angle. (7) Further, according to the present invention, there is provided an electromagnetic wave absorbing sheet characterized in that the thickness of the alloy-based magnetic material is 1/10 to 10 times the skin depth of the alloy-based magnetic material. It is what Here, the desired angle is a range in which the angle deviation of the uniaxial magnetic anisotropy can be set from 0 degree to 90 degrees, and it is practically preferable that it is from 10 degrees to 90 degrees. If it is less than 10 degrees, the effect due to the shift of the uniaxial magnetic anisotropy is small and it is not preferable in practice. A more preferable range is 45 degrees to 90 degrees, and in this range, the effect due to the shift of the uniaxial magnetic anisotropy can be more effectively obtained. (8) NiFe, CoZrNb as an alloy magnetic material
The electromagnetic wave absorbing sheet according to (1), (3) or (5), characterized in that As described above, the present invention is different from the conventional electromagnetic wave absorber in material configuration and the like.

[0005]

According to the electromagnetic wave absorbing sheet of the present invention, a large eddy current loss can be generated by setting the thickness of the alloy-based magnetic body to 1/10 to 10 times the skin depth. As a result, a large electromagnetic wave absorption effect due to eddy current loss can be realized despite the fact that it is sheet-shaped, small and lightweight. Further, since it has a large relative magnetic permeability even at several hundreds MHz or more, it is also effective for unnecessary electromagnetic waves at several hundreds MHz or more.

[0006]

EXAMPLES Next, examples of the present invention will be described. Figure 1
Shows the electromagnetic wave absorbing sheet of the present invention, wherein (a) is 1
(B) is composed of a multilayer structure in which a plurality of layers of the alloy magnetic body 2 and the non-magnetic insulator 3 are alternately laminated, and both have the same effect. Obtainable. In FIG. 1, a sheet substrate 4 made of a non-magnetic insulator is used for holding the electromagnetic wave absorbing sheet. With or without the sheet substrate 4, the same effect can be obtained. (C) is a partially enlarged view of FIG.

The alloy magnetic body 2 has in-plane uniaxial magnetic anisotropy 5 as shown in FIG. FIG. 2 shows the magnetization curves of the alloy-based magnetic body in the case of having in-plane uniaxial magnetic anisotropy (a) and in the case of not having it (b). The solid line and the broken line are magnetization curves in two directions that are orthogonal to each other. In the case of (a), the hard axis direction corresponds to the solid line and the easy axis direction corresponds to the broken line.
Here, a NiFe film was used as the alloy magnetic body.
In (a), excellent soft magnetic characteristics with small hysteresis are obtained, but in (b), large hysteresis appears, and in this case, large relative permeability cannot be obtained. The absorption effect of the electromagnetic wave absorber is proportional to the relative magnetic permeability of the alloy magnetic body. Therefore, it can be understood that it is effective to give the alloy-based magnetic body in-plane uniaxial magnetic anisotropy in that a large relative magnetic permeability can be obtained. Note that only a magnetization process in the hard axis direction responds to a high frequency magnetic field having a frequency of several MHz or more.
Therefore, it can be said that it is effective to give the alloy-based magnetic material in-plane uniaxial magnetic anisotropy as shown in (a) from the viewpoint that it can cope with high frequency unnecessary electromagnetic waves.

FIG. 3 shows the alloy magnetic film thickness t _m and the relative magnetic permeability μ.
_r (: μ _r ′ −j · μ _r ″) is shown. Relative permeability is the value in the direction of the hard axis.
An e film and a CoZrNb film were used. In Fig. 3, μ _r ′,
μ _r ″ is standardized by the static relative permeability μ _r ′ (0), and t _m is standardized by the skin depth δ. δ is the electrical resistance ρ _m , μ _r ′ (0), frequency of the alloy-based magnetic material. f and the magnetic permeability μ _{0 of} vacuum, δ = [2ρ _m / (2πf · μ _r ′ (0) · μ ₀ )] ^1/2 (1) In the case of NiFe film, μ _r ′ (0) = 300
0, ρ _m = 20 μΩcm, and in the case of CoZrNb film,
μ _r ′ (0) = 3000 and ρ _m = 120 μΩcm. As shown in FIG. 3, μ _r ″ has t _m / δ of 0.1 to 1
In the range of 0, it has a value that is 1/100 or more of the maximum value of μ _r ″. When t _m is less than 1/10 of δ, and when t _m exceeds 10 times δ, With the electromagnetic wave absorbing sheet of the present invention, conventional parts (Mn-Zn ferrite plate)
It is not practically preferable because a larger electromagnetic wave absorption effect cannot be realized. From this, it is understood that it is effective to set t _m to a thickness of 1/10 to 10 times δ.

If the thickness of the non-magnetic insulator is thin, electrical breakdown occurs and the characteristics shown in FIG. 3 cannot be obtained. FIG. 4 shows a NiFe film as an alloy magnetic material and Si as a non-magnetic insulator.
The frequency characteristic of the relative permeability when the SiO ₂ film thickness is changed by using the O ₂ film is shown. The relative magnetic permeability is a value in the hard axis direction. NiFe film thickness is NiFe in this frequency band
Membrane skin depth of 0.16 to 1.6 μm, sufficiently thinner than 50 n
m (0.05 μm). SiO ₂ film thickness is 5 nm
However, due to poor electrical insulation, μ _r ′ decreases and μ _r ″ increases from around 30 MHz. On the other hand, the SiO ₂ film thickness is 5
At 0 nm, the ferromagnetic resonance frequency of the NiFe film is 650 MHz.
Up to μ _r ′, the electrical insulation is almost maintained, and when the SiO ₂ film thickness is 100 nm, the insulation effect becomes more reliable. As described above, when the SiO ₂ film is used as the non-magnetic insulator, it is effective to set the thickness of the non-magnetic insulator to 50 nm or more in order to maintain the electrical insulation between the alloy magnetic bodies. The upper limit of the thickness of the non-magnetic insulator is practically 1
It is preferably 0 mm or less. As shown in FIG. 2, in order to realize a large relative magnetic permeability, that is, a large electromagnetic wave absorption effect, and to cope with unnecessary high frequency electromagnetic waves,
It is effective to have uniaxial magnetic anisotropy in the film surface of the alloy magnetic body 2.

As a method of imparting in-plane uniaxial magnetic anisotropy to the alloy magnetic body 2, a method of applying an external magnetic field in the in-plane direction of the alloy magnetic body at the time of producing the alloy magnetic body can be mentioned. . As a method of applying an external magnetic field to the film surface of the alloy magnetic body, for example, as shown in FIG. 5, a method of using a permanent magnet 7 arranged inside a cylindrical can 9 can be mentioned. In this case, the polarity of the external magnetic field direction 8 may be any direction. The magnetization curve of the NiFe film produced by this method is shown in FIG. In FIG. 2A, it can be seen that a clear in-plane uniaxial magnetic anisotropy with the easy magnetic axis as the easy axis is imparted. Examples of methods for applying an external magnetic field include a method using a permanent magnet and a method using an electromagnet.
Both can obtain the same effect.

As another in-plane uniaxial magnetic anisotropy imparting method, after the alloy-based magnetic body is produced without an external magnetic field, the temperature is set higher than that at the time of production, and the alloy-based magnetic body is externally moved in the in-plane direction. The method of applying a magnetic field is mentioned. Further, as another in-plane uniaxial magnetic anisotropy imparting method, there is an oblique deposition method. As shown in FIG.
By depositing in an oblique direction 13 on the upper side, the crystal grain size of the alloy-based magnetic body is made into a flaky shape, and due to the shape magnetic anisotropy,
This is a method of imparting in-plane uniaxial magnetic anisotropy. The same effect can be obtained by any of these methods.

Unwanted electromagnetic waves enter the electromagnetic wave absorber at various directions and angles. As described above, the electromagnetic wave absorbing sheet of FIG. 1 is effective only for unnecessary electromagnetic waves having a magnetic field component in the hard axis direction. As a method that is effective for unnecessary electromagnetic waves in all directions and angles, there is a method in which the uniaxial magnetic anisotropy directions of the alloy magnetic bodies 2 in FIG. Can be mentioned. In addition, FIG.
As shown in, even if a plurality of electromagnetic wave absorption sheets 1 having uniaxial magnetic anisotropy are stacked by arranging the directions of the uniaxial magnetic anisotropy at a desired angle with respect to each other, the same effect can be obtained. be able to. The alloy magnetic material and the non-magnetic insulator are prepared by ion beam sputtering, R
The F-sputtering method, the magnetron sputtering method, the vapor deposition method and the like can be mentioned, and any of them can obtain the same effect. The alloy-based magnetic body 2 is a magnetic material based on Fe, Co, Ni, and the non-magnetic insulator 3 and the non-magnetic insulator sheet substrate 4 are SiO ₂ , AlN, Al.
₂ O ₃ , BN, TiN, SiC, polyethylene naphthalate (PEN), polyethylene terephthalate (PE
T), polyimide, Kapton, and photoresist can be used, and the same effect can be obtained. In addition to the above, the following alloy magnetic materials are also used. N
iFeMo, NiFeCu, NiFeCr, NiFeN
b, NiFeTi, NiFeSi, FeSi, FeC,
FeN, CoFe, FeSiAl, FeB, FeBS
i, CoBSi, FeCoBSi, FeCoNiBS
i, CoXa (Xa: Y, Zr, Hf, Ti, Nb, M
o, W, Re, Ni, Fe, Mn), CoXbXc (X
b: Y, Zr, Hf, Ti, Nb, Mo, W, Re, N
i, Fe, Mn, Xc: Y, Zr, Hf, Ti, Nb,
Mo, W, Re, Ni, Fe, Mn), etc.

Specific examples will be shown below. CoZrNb is used for the alloy magnetic body 2 and SiO is used for the non-magnetic insulator 3.
₂ is a 6 μm thick PET on the non-magnetic insulator sheet substrate 4.
Was manufactured by the ion beam sputtering method. The sputtering conditions were an operating vacuum degree of Ar1 × 10 ⁻⁴ Torr, an acceleration voltage of 1 kV, and a substrate temperature of room temperature to 160 ° C. The external magnetic field was applied by a permanent magnet. CoZrNb during deposition
Since the in-plane uniaxial magnetic anisotropy magnetic field of the film was 20 Oe,
It was reduced to 3 Oe by heat treatment in a rotating magnetic field. Μ _r ′ (0) in the hard axis direction is 3000, ρ _m is 120 μΩc
It was m. The CoZrNb film thickness was set to 2.0 μm that satisfies δ / 10 to 10δ, and the SiO ₂ film thickness was set to 0.1 μm so that electrical insulation can be maintained. In the rotating magnetic field heat treatment, for example, as shown in FIG. 7, in the electric furnace 10, an external magnetic field 11 is applied in parallel to the film surface of the alloy magnetic material so that the electromagnetic wave absorbing sheet is perpendicular to the film surface of the alloy magnetic material. It is a heat treatment method in which the alloy-based magnetic material is installed so that the direction of the uniaxial magnetic anisotropy and the direction of the external magnetic field change with the passage of time. The heat treatment was performed in a nitrogen gas atmosphere, the heat treatment temperature was 350 ° C., the heat treatment time was 1 hour, the magnitude of the external magnetic field was 100 Oe, and the rotation speed was 4 rpm.

FIG. 8 shows the frequency dependence of the relative permeability in the hard axis direction. At 10 MHz or higher, μ _r ″> μ _r ′, and the μ _r and μ _r ″ values are significantly larger than those of the Mn—Zn ferrite shown in FIG. Further, as is clear from the figure, μ _r ″ maintains a large value even at several hundred MHz or more, and thus it is also effective for unwanted electromagnetic waves at several hundred MHz or more. NiFe in 2
An example in which SiO _{2 is used} for the non-magnetic insulator 3 and PEN having a thickness of 6 μm is used for the non-magnetic insulator sheet substrate 4 is prepared by a vapor deposition method. The substrate temperature was room temperature to 160 ° C., and the external magnetic field was applied by an electromagnet. The in-plane uniaxial magnetic anisotropy magnetic field of NiFe was 3 Oe, μ _r ′ (0) in the hard axis direction was 3000, and ρ _m was 20 μΩcm. The NiFe film thickness was set to 20 μm satisfying δ / 10 to 10δ, and the SiO ₂ film thickness was set to 0.1 μm capable of maintaining electrical insulation. Figure 9
Shows the frequency dependence of relative permeability in the hard axis direction. 10M
Above Hz, μ _r ″> μ _r ′, and the μ _r and μ _r ″ values are significantly larger than those of the Mn—Zn ferrite of FIG. Further, as is clear from the figure, since μ _r ″ maintains a large value even at several hundred MHz or more, several hundred M
It can be seen that it is also effective for unnecessary electromagnetic waves of Hz or higher.

[0015]

As described above, according to the electromagnetic wave absorbing sheet of the present invention, a great effect can be realized in spite of the sheet shape, the small size and the light weight. Furthermore, hundreds of MH
It is also effective for unnecessary electromagnetic waves of z or more. Further, the manufacturing is easy, and by displacing the directions of the uniaxial magnetic anisotropy at a desired angle with respect to each other, a large electromagnetic wave absorbing effect can be exerted against unnecessary electromagnetic waves incident in various directions and angles. You can

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of an electromagnetic wave absorbing sheet of the present invention, in which (a) is a single-layer alloy-based magnetic body, and (b) is a plurality of alloy-based magnetic bodies and non-magnetic insulators alternately. When the layers are stacked, (c) shows a partially enlarged view of (b).

FIG. 2 is a diagram showing a magnetization curve, where (a) shows a case with uniaxial magnetic anisotropy, and (b) shows a case without it.

FIG. 3 is a diagram showing the dependency of relative magnetic permeability on the thickness of an alloy-based magnetic body.

FIG. 4 is a diagram showing the frequency dependence of the relative permeability when the thickness of the non-magnetic insulator is changed.

FIG. 5 shows a method of applying an external magnetic field to the film surface of an alloy magnetic body.

FIG. 6 is a diagram showing an example of an electromagnetic wave absorbing sheet of the present invention.

FIG. 7 shows a method of performing heat treatment in a rotating magnetic field.

FIG. 8 is a diagram showing frequency dependence of relative permeability.

FIG. 9 is a diagram showing frequency dependence of relative permeability.

FIG. 10 is a diagram showing frequency dependence of relative permeability in a conventional electromagnetic wave absorber (Mn—Zn ferrite).

FIG. 11 shows a diagonal deposition method of raw material particles.

[Explanation of symbols]

 1 Electromagnetic Wave Absorption Sheet 2 Alloy Magnetic Material 3 Non-Magnetic Insulator 4 Non-Magnetic Insulation Sheet Substrate 5 Easy Axis Direction 6 Non-Magnetic Insulation Sheet Substrate 7 Permanent Magnet 8 External Magnetic Field Direction 9 Cylindrical Can 10 Electric Furnace 11 External Magnetic Field 12 Substrate 13 Incident direction of raw material particles

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[Procedure amendment]

[Submission date] June 3, 1994

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Fig. 11

[Correction method] Added

[Correction content]

FIG. 11

Claims (8)

[Claims] 1. An electromagnetic wave comprising a single-layer alloy magnetic body, wherein the alloy magnetic body has uniaxial magnetic anisotropy in a direction parallel to a film surface of the alloy magnetic body. Absorption sheet. 2. An alloy magnetic body bonded to a non-magnetic insulating sheet substrate, wherein the alloy magnetic body has uniaxial magnetic anisotropy in a direction parallel to the film surface of the alloy magnetic body. A plurality of electromagnetic wave absorbing sheets are stacked, and the directions of the uniaxial magnetic anisotropy of the alloy-based magnetic body in each electromagnetic wave absorbing sheet are offset from each other by a desired angle. Electromagnetic wave absorption sheet 3. An alloy magnetic body and a non-magnetic insulator are alternately laminated to form a multilayer body, and the alloy magnetic body is uniaxial in a direction parallel to the film surface of the alloy magnetic body. An electromagnetic wave absorption sheet having magnetic anisotropy. 4. The electromagnetic wave absorbing sheet according to claim 3, wherein the directions of uniaxial magnetic anisotropy of the alloy-based magnetic body are offset from each other by a desired angle. 5. A first alloy-based magnetic material is deposited on a substrate, a non-magnetic insulator is then formed thereon, and then a second alloy-based magnetic material is deposited on the non-magnetic insulator. In the multi-layered sheet having at least three layers, each of the alloy-based magnetic bodies has uniaxial magnetic anisotropy in a direction parallel to the film surface. 6. The electromagnetic wave absorption sheet according to claim 5, wherein the directions of the uniaxial magnetic anisotropy of the respective alloy magnetic bodies are displaced at a desired angle. 7. The thickness of the alloy-based magnetic material is 1/10 to 10 times the skin depth of the alloy-based magnetic material, and the thickness is 1 to 3 or 5. Electromagnetic wave absorption sheet. Where the skin depth δ is
The depth from the surface that can penetrate into the alloy-based magnetic film (alloy-based magnetic layer), the electrical resistance ρ _{m of} the alloy-based magnetic film (layer), the frequency f, the static relative permeability μ _r ′ (0), Using the magnetic permeability μ _{0 of} vacuum, δ = [2ρ _m / (2πf · μ _r ′ (0) · μ ₀ )] ^1/2 . 8. An alloy-based magnetic material comprising NiFe, CoZ
The electromagnetic wave absorbing sheet according to claim 1, 3 or 5, wherein rNb is used.