JP2784386B2 - Magnetic multilayer film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic multilayer film for a high-frequency magnetic device.

[0002]

2. Description of the Related Art As a core material of a high-frequency magnetic device such as a coil or a transformer, a magnetic material having a constant large relative permeability and a small loss up to as high a frequency as possible is required. The relative magnetic permeability μr is represented by μr = μr′−j · μr ″ (1), where μr ′ is a real part and μr ″ is an imaginary part. Here, (−1) ^1/2 = j. Since μr ′ corresponds to the effective relative magnetic permeability and μr ″ corresponds to the loss, respectively, the core material is required to have a high μr ′ and a constant μr ″ up to high frequencies and a low μr ″. When a high-frequency magnetic field is applied to a magnetic material, a current flows in the magnetic material, damping the change in magnetization of the magnetic material, and causing loss. This is called eddy current loss. The eddy current loss becomes remarkable when the thickness of the magnetic body is larger than the skin depth δ expressed by the equation (2). δ = {2ρm / (2πf · μr ′ · μ ₀ )} ^1/2 (2) where ρm is the resistivity of the magnetic material, f is the frequency, and μ ₀ is the magnetic permeability of vacuum. Since the ferrite magnetic material has a high ρm, the skin depth δ increases, and eddy current loss does not pose a problem in a frequency band of 100 MHz or less. For these reasons, a ferrite-based magnetic material has been conventionally used as a main material of a core for a high-frequency magnetic device. FIG. 5 shows the characteristics of the conventional material. 5, the horizontal axis represents frequency, and the vertical axis represents μr ′, μr ″. In a typical ferrite (Ni—Zn), the static relative magnetic permeability μr ′ (0) is 35,
The ferromagnetic resonance frequency fk is 300 MHz,
Μr ′ begins to decrease and μr ″ starts to increase from around Hz. On the other hand, in ferroxplanar ferrite, μr ′ (0) is 35 and fk is 700 MHz. (Reference: Electronic materials series "Ferrite" Hiraga, Okutani, Ojima, 1986, Maruzen). In recent years, with the demand for downsizing and high frequency of magnetic devices, development of magnetic materials usable in a high frequency band of 100 MHz or more has been required. However, as described above, the ferrite-based magnetic material, which is a conventional material, has a decrease in μr ′ from 100 MHz to several hundred MHz,
Because of the rapid increase of r ″, it cannot be used above 100 MHz, which makes it difficult to realize a small-sized, high-frequency magnetic device with an operating frequency of 100 MHz or more.

[0003]

SUMMARY OF THE INVENTION The present invention has been proposed in order to improve the above-mentioned drawbacks. It is an object of the present invention to provide a conventional high-frequency magnetic material having a relative permeability in a frequency band of 100 MHz to several hundred MHz. An object of the present invention is to provide a magnetic multilayer film exhibiting high relative permeability and low loss, which solves the problem that the loss is increased and the loss is increased.

[0004]

According to the present invention, there is provided a magnetic multilayer film comprising a magnetic substrate and a non-magnetic insulator alternately laminated on a substrate, wherein the magnetic multilayer film has a stripe shape. Long side direction and short side direction
The most main feature is that a stress difference is generated between the two directions and the film has anisotropy in film stress . The material composition and structure are different from the conventional materials.

[0005]

According to the present invention, the ferromagnetic resonance frequency, which is the upper limit frequency, can be increased in frequency, so that high specific permeability and low loss can be realized in a high frequency band of several GHz.

[0006]

Next, an embodiment of the present invention will be described. FIG.
Is a diagram showing an embodiment of the magnetic multilayer film of the present invention,
(A) is a perspective view and (b) is a partially enlarged view of c in FIG. (A). A magnetic multilayer film 3 in which magnetic materials 1 and non-magnetic insulators 2 are alternately stacked on a substrate 4 is formed, and the magnetic multilayer film has a stripe shape. When an anisotropic film stress σf acts on a magnetic material having a magnetostriction constant λs, the magnetic material has an anisotropic magnetic field Hst expressed by the following equation due to the strain magnetic anisotropy.
Occurs. Hst = 4π · 2 ｛(3/2) σf · λs｝ / 4πMs (3) where 4πMs is the saturation magnetization of the magnetic material. Further, the ferromagnetic resonance frequency fk of this magnetic material is as follows: fk = (γ / 2π) ｛Hst (4πMs + Hst)｝ ^1/2 (4) Here, γ is a gyro magnetic constant. Film stress is mainly caused by the difference in thermal expansion between the film and the substrate. In general, the film stress is isotropic in the film plane. Therefore, in order to generate the anisotropic magnetic field Hst, the film stress needs to have anisotropy. When the shape of the magnetic multilayer film is a stripe as shown in FIG. 1, the stress is released in the short side direction of the stripe pattern and the stress remains in the long side direction, so that anisotropy occurs in the film stress. When the magnetic multilayer film is used at a frequency lower than the ferromagnetic resonance frequency fk, the skin depth at fk is
From equation (2), {2ρm / (2πfk · μr ′ ·
μ ₀ )｝ ^1/2 . By making the thickness of the magnetic material equal to or less than the skin depth, it is possible to avoid eddy current loss at or below the ferromagnetic resonance frequency fk. In FIG. 1, the thickness of the magnetic body is set to be equal to or less than the skin depth. Also,
If the thickness of the non-magnetic insulator is thin and the electrical insulation between the magnetic bodies is incomplete, a current flows between the magnetic bodies, causing eddy current loss. In FIG. 1, the thickness of the non-magnetic insulator is set to be equal to or greater than the thickness that can maintain electrical insulation between the magnetic bodies.
Since the upper limit of the frequency of μr ′ is determined by the ferromagnetic resonance frequency fk, the higher the fk, the higher the performance of the magnetic material. To increase the ferromagnetic resonance frequency fk,
It is necessary to increase the anisotropic magnetic field Hst from the equation (4), that is, to increase the anisotropic film stress σf and the magnetostriction constant λs from the equation (3). Since the anisotropic stress does not depend much on the material, it is advantageous to select a material having a large magnetostriction constant as the magnetic material. In order to increase μr ′, it is advantageous to select a magnetic material having a large saturation magnetization of 4πMs.

Next, a specific example will be described. As a magnetic material, 4π
CoFe alloy [Co with large values of both Ms and λs
50 at. %] (Hereinafter referred to as a CoFe alloy). Further, SiO ₂ was used as the non-magnetic insulator.
SiO ₂ has a thickness of 0.05 μm (50 nm) or more that can maintain electrical insulation between magnetic bodies. In the following example, the SiO ₂ film thickness is set to 0.1 μm (100 n
m). FIG. 2 shows CoFe / SiO ₂ [50/100
nm] shows the frequency characteristics of the relative magnetic permeability in the multilayer film. 2, the horizontal axis represents frequency, and the vertical axis represents μr ′, μr ″. An anisotropic magnetic field was generated in the y direction in FIG. 1 and the magnitude thereof was about 200 Oe. 3) Formula C
oFe alloy value 4πMs = 2.45 Tesla, λs +
1.3 × 10 ⁻⁴ , approximately equal to the value of Hst into which σf 圧 縮^{−10 9} dyn / cm ² (compressibility) is substituted. Μr ′ (0) of the CoFe alloy alone is 120,
r '(0) is volume-averaged to 40. At about 7 GHz, μr ′ sharply decreases and μr ″ sharply increases, and it can be seen that ferromagnetic resonance occurs near this.
7 GHz, which is consistent with the experimental results. Co
Value in Fe alloy, ρm = 20 μΩcm, μr ′
Substituting (0) = 120 into equation (2) gives δ at 7 GHz
Is 0.25 μm. In FIG. 2, the film thickness of the CoFe alloy is 0.05 μm (50 nm), which is a sufficiently small value as compared with δ, so that no eddy current loss occurs below the ferromagnetic resonance frequency fk. FIG. 2 shows that μ in the frequency band of 7 GHz or less.
Good characteristics in which r ′ = 40 is obtained are constant. When this is compared with the characteristics of the conventional material in FIG. 5, CoFe / S
In the iO ₂ multilayer film, μr ′ (0) is almost the same,
Regarding frequency characteristics, about 70% of Ni-Zn ferrite
It can be seen that the performance is 18 times that of the ferrox-plana ferrite. In this embodiment, λs> 0 and σ
Although the case where f <0 is shown, similarly, λs> 0 and σf>
1 is anisotropic in the z direction in FIG. 1; λs <0 and σf <0 in the z direction in FIG. 1; and λs <0 and σf> 0 in the y direction in FIG. An activating magnetic field is generated. The magnitude of σf caused by the difference in thermal expansion is ± 10 ⁹ d
Since it is yn / cm ² approximately, | when ~10 ^-6, | λs
The frequency becomes fk to several hundred MHz, which is almost the same as that of the conventional material shown in FIG. Therefore, it is effective to satisfy | λs |> 10 ⁻⁶ in order to realize characteristics exceeding conventional materials.
As described above, in a magnetic multilayer film in which a magnetic material and a non-magnetic insulator are alternately laminated, the magnetic multilayer film has a stripe shape, so that a magnetic material having excellent high-frequency characteristics can be obtained as compared with a conventional material. did it.

The same effect can be obtained not only with a plurality of magnetic multilayer stripes as shown in FIG. 1, but also with a single stripe, as shown in FIG. In addition, the same effect can be obtained even if it is bent in a meandering or zigzag shape as shown in FIGS. In the figure, 3 indicates a magnetic multilayer film, and 4 indicates a substrate. In order to increase the ferromagnetic resonance frequency, it is necessary to increase the magnetostriction constant. However, in order to achieve characteristics exceeding those of conventional materials, it is effective to set | λs |> 10 ^−6. is there. Further, as a magnetic material, other than CoFe, Fe, Ni, Co, Zr, N
b, Y, Hf, Ti, Mo, W, Ta, Si, B, Re
Materials consisting of one or more elements,
As a non-magnetic insulator, besides SiO ₂ , AlN, Al
The same effects as described above can be obtained by using each of ₂ O ₃ , BN, TiN, and SiC. Further, as a method of generating the strain magnetic anisotropy in the magnetic material, a method of applying an external force in one direction of the magnetic multilayer film can be considered, and the same effect as described above can be obtained by this method. As described above, the magnetic multi-layered film according to the present invention is improved in that it exhibits high relative permeability and low loss up to high frequencies as compared with conventional materials.

[0009]

As described above, according to the present invention, the magnetic multilayer film according to the present invention, on a substrate, the magnetic multilayer film which is a magnetic body and a non-magnetic insulator formed by laminating alternately, the magnetic multilayer film in a stripe shape By processing, long side direction and short side direction
By causing an anisotropy of the film stress by causing a stress difference in the
In a high frequency band of several hundred MHz to several GHz, there are advantages of high relative permeability and low loss. Therefore, the present magnetic multilayer film is useful as a core material of a small high-frequency magnetic device having an operating frequency of 100 MHz or more.

[Brief description of the drawings]

FIG. 1 is a view showing an embodiment of a magnetic multilayer film of the present invention,
(A) is a perspective view, (b) is a partial enlarged view.

FIG. 2 shows frequency characteristics of relative magnetic permeability in the magnetic multilayer film of the present invention.

FIG. 3 shows another embodiment of the present invention.

FIG. 4 shows another embodiment of the present invention.

FIG. 5 shows frequency characteristics of relative magnetic permeability in a conventional material.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic body 2 Nonmagnetic insulator 3 Magnetic multilayer film 4 Substrate

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-283503 (JP, A) JP-A-2-121213 (JP, A) JP-A-49-78877 (JP, A) (58) Investigation Field (Int.Cl. ⁶ , DB name) H01F 10/16

Claims (4)

(57) [Claims] To 1. A substrate, in the magnetic multilayer film formed by laminating a magnetic material and a nonmagnetic insulator alternately magnetic material having a magnetostriction, this said magnetic multilayered film is processed into a stripe shape
Causes a stress difference between the long side direction and the short side direction, resulting in film stress.
A magnetic multilayer film having anisotropy of: " 2. A magnetic multilayer film according to claim 1, wherein the magnetic multilayer film has one or more stripe shapes bent in a straight line, meandering shape, or zigzag shape. 3. The magnetic multilayer film according to claim 1, wherein the absolute value of the magnetostriction constant of the magnetic material is 10 ⁻⁶ or more. 4. When the magnetic multilayer film is used in a frequency band equal to or lower than the ferromagnetic resonance frequency, the thickness of the magnetic material is equal to or less than the skin depth at the ferromagnetic resonance frequency, and the thickness of the non-magnetic insulator is equal to or less than the magnetic depth. 4. The magnetic multilayer film according to claim 1, wherein the thickness is not less than a thickness capable of maintaining electrical insulation between the bodies.