JP4630882B2 - Uniaxial magnetic anisotropic film - Google Patents

Description

  The present invention relates to a uniaxial magnetic anisotropic film having a large anisotropic magnetic field, a high electrical resistivity, and a high saturation magnetization and exhibiting excellent soft magnetism in a high frequency band. Furthermore, the present invention intends to provide a transformer or inductor made of this magnetic film.

  In recent years, efforts have been actively made to increase the operating frequency of electronic devices. However, there are no known magnetic materials that have been used in transformers, inductors, magnetic heads, etc., which have sufficient characteristics in the high frequency band, and therefore there are many restrictions on the use of these components in the high frequency band. It was. In general, when a high frequency band of 1 MHz or higher is reached, a large loss occurs due to eddy current flowing in the magnetic material itself. Metallic magnetic materials have low eddy currents due to their low electrical resistance, making them difficult to use in high frequency bands. On the other hand, oxide-based magnetic materials such as ferrite and garnet have a very large electrical resistance, so that loss due to eddy current is relatively unlikely to occur. However, it is difficult to obtain a material having a high magnetic permeability, and since the saturation magnetic flux density is small, the natural resonance frequency is low, and there are many restrictions on the use in the high frequency band.

There are great expectations for magnetic materials having a high saturation magnetic flux density and good high-frequency soft magnetic properties, and various methods for increasing the electrical resistance of metal-based magnetic materials have been proposed so far. For example, a method for obtaining an amorphous alloy film in which ceramics are dispersed by simultaneous sputtering of metal and ceramics is proposed by Patent Document 1: Japanese Patent Application Laid-Open No. 60-152651, and Non-Patent Document 1: J. Appl. Phys. 63 (8), 15 April 1988, Fe-B ₄ C-based dispersion film, Non-Patent Document 2: J. Appl. Phys., 67 (9), 1 May 1990, Co. ₄ Fe. ₄ B. _{A 2-} SiO ₂ dispersion film is shown as having both high specific resistance and soft magnetism. In addition, a thick single-layer film does not show good soft magnetic characteristics. By making a Co. ₉₅ Fe. ₀₅ -BN dispersion film a magnetic layer of 0.1 μm or less, soft magnetic characteristics can be obtained. Japanese Patent Application Laid-Open No. 4-142710 discloses that soft magnetic characteristics can be obtained even with a thick film by laminating the intermediate layers.

On the other hand, Japanese Patent Application Laid-Open No. 54-94428 discloses a method for obtaining an amorphous alloy film having high electrical resistivity by reactive sputtering with N ₂ or O ₂ gas. In addition, it has been found in many alloy systems that the addition of N ₂ gas during the production of a thin film is effective in improving soft magnetic properties. For example, Non-Patent Document 3: IEEE TRANS. On MAG. MAG-20 1451 (1984).
JP-A-60-152651 JP-A-4-142170 J. Appl. Phys. 63 (8), 15, April 1988 J. Appl. Phys. 67 (9), 1 May 1990 IEEE TRANS. On MAG. MAG-20 1451 (1984) Japan Society of Applied Magnetics, 18, 303 (1994) Journal of the Japan Institute of Metals, 18, 303 (1994) Journal of Japan Society of Applied Magnetics, Vol.17, p497 (1993) Journal of Japan Society of Applied Magnetics, Vol.15, p327 (1991)

A magnetic material used in a high frequency band is required to have both an electric resistance and a saturation magnetic flux density, and an anisotropic magnetic field having an appropriate magnitude. Further, it is desirable that the magnetostriction constant of the material is as close to zero as possible in order to minimize the deterioration of the soft magnetic characteristics due to processing strain and the like. However, the Fe / B ₄ C dispersion film and the Co. ₄ Fe. ₄ B. ₂ / SiO ₂ dispersion film having high electrical resistance, which have been reported so far, are both soft magnetic in the amorphous phase. Although it was shown that the characteristics were excellent, it had a large positive magnetostriction of 10 ⁻⁵ or more. On the other hand, a Co. ₉₅ Fe. ₀₅ / BN dispersion film was developed for the purpose of achieving both zero magnetostriction and high electrical resistance, but this system has a large saturation magnetization and coercive force in a thick monolayer film of 0.1 μm or more. It did not show soft magnetic properties. Therefore, it has been shown that soft magnetic properties can be obtained by laminating via a non-magnetic layer, but on the other hand, the saturation magnetization of the entire film is reduced and the process is also complicated. It included problems. In addition, conventional soft magnetic materials have not taken into account an anisotropic magnetic field, which is an important characteristic equivalent to a high electrical resistivity.

  Very recently, it has been found that a Co—Al—N alloy film having a granular structure has both zero magnetostriction, high electrical resistance, and a moderately anisotropic magnetic field (30 to 40 Oe) (Non-patent Document 4: Journal of Japan Society of Applied Magnetics, 18, 303 (1994)). However, since the saturation magnetic flux density of the film is not so high as about 8 kG, the natural resonance frequency is about 1 GHz. In addition, it was found that the Co—O-based granular film improves soft magnetic characteristics and contains a large anisotropic magnetic field (Hk) of around 200 Oe when Pd is contained at about 10 at.% Or more (Non-patent Document 5: Abstracts of the Japan Institute of Metals, 1993 Autumn Meeting, 234). Large Hk increases the natural resonance frequency of the magnetic permeability. However, since Bs is substantially constant, if Hk is too large, the magnetic permeability becomes too small to be suitable for practical use. In order to control the magnitude of Hk of this film and obtain a film exhibiting an arbitrary magnetic permeability, it was necessary to perform heat treatment in a plurality of processes.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a soft magnetic film having a large electric resistance, a saturation magnetization, an anisotropic magnetic field of an appropriate magnitude, and a low magnetostriction. .

As a result of diligent efforts in view of the above circumstances, the inventors of the present invention made an alloy target composed of two or more elements by a reactive sputtering method using an RF magnetron sputtering apparatus in a mixed gas of Ar + O _2. It has been found that a good soft magnetic film can be obtained even with a 1 μm thick single-layer film by forming the film, and the present invention has been achieved.
The features of the present invention are as follows.
As a first invention, it is represented by the general formula (Co _1-a Fe _a ) _{100-X -Y} M _X O _Y , where M is Dy, Er, Gd, Hf, Li, Mg, Nd, Sc, Sr, Tm, One or more elements selected from Y, Yb, Zr and Sm , the composition ratio a is a <0.3, X and Y are atomic%, 6 ≦ X <12, 22 ≦ Y < 37, comprising 30 ≦ X + Y <48 and a small amount of impurities, having an anisotropic magnetic field of 30 Oe to 100 Oe, an electrical resistivity of 300 μΩcm to 1500 μΩcm, and a saturation magnetic flux density of 8 kG or more. A uniaxial magnetic anisotropic film characterized by

As a second invention, it is represented by the general formula Co _{100 -X -Y} M _X O _Y , where M is Dy, Er, Gd, Hf, Li, Mg, Nd, Sc, Sr, Tm, Y, Yb and Zr 1 or 2 or more elements selected from the above, and the composition ratios x and y are 8% in the atomic%, 8 <x <12, 20 <Y <37, and 36 <x + y <48. A uniaxial magnetic anisotropic film comprising a small amount of impurities, having an anisotropic magnetic field of 30 Oe to 100 Oe, an electrical resistivity of 300 μΩcm to 1500 μΩcm, and a saturation magnetic flux density of 8 kG or more was found.

As a third invention, the uniaxial magnetic anisotropic film according to claim 1 or 2, wherein the M element further contains Al.

A fourth invention, the general formula _{(Co 1 -aFea) 100- X -} Y M X O Y film or Co ₁₀₀ - _X - in _Y M _X O _Y film, the absolute value of the generated heat of the size of the MO compounds 1000kJ The uniaxial magnetic anisotropy film according to claim 1 or claim 2, characterized in that the M element is larger.

5. The uniaxial magnetic property according to any one of claims 1 to 3, wherein the fifth invention has a nano-granular structure of 100 mm or less comprising Co phase fine particles and an oxide phase of M element at the grain boundary. I found an isotropic membrane.

The sixth invention is characterized in that the magnitude of the anisotropic magnetic field of the film can be controlled in the range of 30 Oe or more and 100 Oe or less by performing heat treatment in a rotating magnetic field or in a static magnetic field. The uniaxial magnetic anisotropic film described in item 1 was found.

According to a seventh aspect of the present invention, the uniaxial magnetic anisotropic film according to any one of claims 1 to 3 is provided, wherein a pair of permanent magnets is disposed in a substrate holder and the film is formed.

As an eighth invention, the transformer comprising the uniaxial magnetic anisotropic film according to any one of claims 1 to 6 has been found.

As an ninth invention, the inductor comprising the uniaxial magnetic anisotropic film according to any one of claims 1 to 6 has been found.

(Function)
The magnetic film of the present invention needs to have a granular structure composed of nano-sized metal fine particles and a thin grain boundary surrounding them. Magnetic properties are strongly related to the structure. That is, even if the magnetic particles have a large anisotropy energy, if the nano-sized in size, for the easy axis of each particle has a random orientation, magnetic bodies in a region The magnetic anisotropy energy approaches zero and becomes soft magnetism. However, in the case of a Co-based alloy, when the particle size is 100 mm or more, perpendicular magnetic anisotropy starts to occur in the film, and soft magnetism cannot be obtained. It is desirable that the grain boundary, which is another key to softening, be thin and clear. When the grain boundary is thick, the magnetic interaction between the grains becomes small and soft magnetism cannot be obtained. For this purpose, the concentration of the elements forming the grain boundary, if the metal particles are Co exceeds 8at.%, If the metal particles are Co-Fe is 6at.% Or more and less than 12at.%, In addition, the heat of formation of the oxide needs to be remarkably greater than the heat of formation of the oxide of Co. Specifically, it is desirable that the absolute value of the generated heat is 1000 kJ or more. In the case of 1000 kJ or less, the formation of grain boundaries cannot be made clearly. Another element that contributes to the grain boundary is oxygen. When the metal particle is Co, the oxygen concentration is 27 at.% Or less, and when the metal particle is Co-Fe, less than 22 at.%, An oxide of M element with a stoichiometric ratio is generated and a grain boundary is formed. Not enough. On the other hand, when the concentration exceeds 37 at.%, Not only the M element but also the Co element starts to be oxidized, so that the magnetization of the film decreases and soft magnetism does not appear. Furthermore, the total amount of M component and oxygen is 30 at.% Or more and less than 48 at.% When the metal particles are Co-Fe, and more than 36 at.% And less than 48 at.% When the metal particles are Co. is there.

On the other hand, in order to set the natural resonance frequency of the magnetic permeability of the uniaxial magnetic anisotropic film of the present invention to 1 GHz or more, the magnitude of the anisotropic magnetic field of the film is desirably 30 Oe or more. However, the resonance frequency becomes higher at 100 Oe or more, but the magnetic permeability becomes too small and the electrical output becomes small, which is a practical problem. An alloy containing 30 at.% Or more of Fe has a magnetostriction of 10 ⁻⁵ or more, and the soft magnetic properties of the film deteriorate due to the generated strain in microfabrication or the like. When the saturation magnetization is 8 kG or less, the value of the magnetic permeability becomes small, which is not appropriate. On the other hand, in order to have Bs of 13 kG or more, the M element concentration in the film must be lowered, and it becomes difficult to obtain a granular structure. As a result, the electric resistance of the film is low and it is difficult to obtain soft magnetism. Another constant that degrades the frequency dependence of permeability is eddy current loss. This is related to the electrical resistance of the film, and the higher the electrical resistance, the smaller the eddy current loss. If the electrical resistivity of the film is 300 μΩcm or more, the eddy current loss is about 1/2 or less that of the conventional material. A larger electrical specific resistance value is desirable, but when it is 1500 μΩcm or more, a paramagnetic component appears in the film, which interferes with the magnetization rotation and degrades the frequency dependence of the magnetic permeability.

Next, reference examples and examples of the present invention will be described.
Reference example 1
Using an RF magnetron sputtering apparatus, a target having a diameter of 4 inches was sputtered to produce a thin film having a thickness of about 2 μm. The target composition at this time was Co ₈₅ Al ₁₅ and # 7059 glass manufactured by Corning Inc. having a thickness of about 0.5 mm was used for the substrate. The sputtering pressure during film formation was 1 to 10 mTorr, and the flow rate ratio of oxygen to argon gas was 0 to 3%. Further, a magnetic field of about 130 Oe is applied by a pair of permanent magnets so that uniaxial magnetic anisotropy is imparted to the substrate during film formation. Note that the sputtering power was constant at 200W.

  The structure of the resulting sample was examined using an X-ray diffraction device (XRD). Fig. 1 shows the XRD results of films prepared with different amounts of oxygen. As the oxygen concentration increases, the main peak that appears at around 46 degrees broadens, indicating that miniaturization has occurred. In order to obtain further knowledge on this matter, the structure was observed with an electron microscope. The result is shown in FIG. Similar to the XRD results, the film became finer as the oxygen concentration increased, and it was found that the film consisted of a network-like structure consisting of fine particles with a particle size of 50 mm or less and grain boundaries with a thickness of about 10 mm. As a result of analyzing these two phases by energy dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS), the fine particles consist mainly of the Co phase and the grain boundaries consist of the Al-O ceramic phase. I understood it. The selective oxidation of Al and the presence of an oxidized phase were also confirmed by an X-ray spectrometer (ESCA).

Next, the DC magnetic properties of the film were measured with a vibration magnetometer (Fig. 3). The two data in the figure represent the results of measurement with excitation parallel (//) and perpendicular (⊥) to the magnetic field application direction during film formation. The sample had uniaxial magnetic anisotropy parallel to the applied magnetic field direction during film formation, and the magnitude of the anisotropic magnetic field (Hk) was 83 Oe. The coercive force (Hc) in the difficult direction is 2.2 Oe and the saturation magnetic flux density (Bs) is as large as about 11 kG, indicating that the Co—Al—O film is a good soft magnetic film. The specific electric resistance of the membrane ([rho) result of measurement by a direct current four-terminal method, showed a large value of 980Myuomegacm. Next, the frequency dependence of the permeability in the hard axis direction was measured by the parallel line method. This method is disclosed in Non-Patent Document 6: Journal of Japan Society of Applied Magnetics, vol. 17, p497 (1993). The results are shown in FIG. Each point in the figure is an actual measurement value, and a solid line is a theoretical value obtained by a method disclosed in Non-Patent Document 7: Journal of Japan Society of Applied Magnetics, vol.15, p327 (1991). Since Hk is large, the real part of the magnetic permeability is not so large, but it shows good frequency characteristics that do not deteriorate to 500 MHz. This is because the thin film of the present invention has a high saturation magnetic flux density and anisotropy magnetic field, so that the natural resonance frequency is very high and is homogeneous, and the result is close to the theoretical value. .

As a comparative example, a Co—Al—O thin film was produced under the same conditions as in Reference Example 1 using a target having a composition of Co ₇₅ Al ₂₅ . Although the Hc of the BH loop of the obtained film is small, the magnetization curve has a shape that is mainly superparamagnetic, and it does not show uniaxial magnetic anisotropy, so the μ-f characteristics deteriorate. To do.

Example 1
A Co-YO film was fabricated using the same equipment as the reference example. The difference from the reference example in the film formation conditions and the evaluation method is that a composite target in which a Y ₂ O ₃ chip (5 × ⁵ mm ² ) is pasted on a Co target is used as a target. The XRD and TEM results of the resulting film also consisted of a two-phase network-like microstructure similar to that of Reference Example 1. The structural difference from Reference Example 1 is that both the grains and grain boundaries of the Co-YO film are in an amorphous phase.

  FIG. 5 shows the result of magnetic properties of the obtained film. The Co-YO film, like the Co-Al-O film, has uniaxial magnetic anisotropy parallel to the magnetic field direction applied at the time of film formation, and its Hk is 80 Oe. Since the linearity is good, it is assumed that there is almost no anisotropic dispersion of the film. Bs was as large as 11.6kG and Hc was as small as 1.4Oe, and the film showed good soft magnetic properties. However, ρ is 305 μΩcm, which is small compared to that of the Co—Al—O film. However, since there is almost no disorder in the anisotropy, the actually measured μ-f characteristic shown in FIG. 6 matches the theoretical value. Shows good high frequency magnetic properties.

Example 2
A Co-Sm-O film was produced by high-frequency sputtering of a composite target in which Sm ₂ O ₃ chips were evenly placed on a Co disk so that the coating rate was 50%. Other film forming conditions and evaluation methods were the same as in Reference Example 1. The obtained sample was confirmed by XRD to consist of two fine phases, an amorphous ceramic phase and an amorphous metal phase. In FIG. 7, the sample is magnetized in the direction of the magnetic field applied during film formation, and its anisotropic magnetic field is 71 Oe. In addition, Bs is 10.4 kG, and the coercive force Hc = 4.5 Oe in the difficult direction is small and shows good soft magnetic properties. The electrical resistivity value is as large as 1060 μΩcm. Reflecting these results, the Co—Sm—O film exhibits good high-frequency soft magnetic properties as shown in FIG.

Reference example 2
FIG. 9 shows the results of Hk in which a Co ₆₀ Al ₁₁ O ₂₉ film produced by the same method as in Reference Example 1 was heat-treated in a magnetic field in a vacuum or in an inert gas. Hk when subjected to static magnetic field treatment (UFA) increases slightly from around 200 ° C, the temperature at which structural relaxation begins. On the other hand, the Hk of the film processed in a rotating magnetic field (RFA) starts to decrease from around 150 ° C. and becomes zero at 250 ° C. or higher. From these results, a uniaxial magnetic anisotropic film having an arbitrary size Hk in the range of 0 to 100 Oe can be obtained by performing heat treatment combining UFA and RFA. As an example, FIG. 10 shows the results of μ-f characteristics of a film that has been subjected to RFA at 250 ° C. and then subjected to UFA at 150 ° C. As is apparent from the figure, the obtained film exhibits excellent high-frequency dependence of permeability close to the theoretical value.

  A sample with a small amount of oxygen, that is, a sample with a small electrical specific resistance value of ˜100 μΩcm exhibits a magnetization behavior that has an easy magnetization component in a direction perpendicular to the film surface. Moreover, the coercive force of the film is as large as 20 Oe or more. Further, these films are hardly improved by any heat treatment.

  Table 1 shows the composition and characteristic values of typical films of the present invention.

  The present invention is an alloy-based film having a wide range of composition, a moderately large anisotropic magnetic field, a large electric resistance, a large saturation magnetization, an excellent HF characteristic, and a uniaxial magnetic anisotropy. A magnetic thin film can be provided. Further, since the thin film of the present invention does not need to be a multilayer film in particular, it does not require a special process or device, and thus is suitable for transformers and inductors operating in a high frequency band, and its industrial significance is large.

FIG. 1 is an X-ray diffraction pattern (Y = 0 to 60) showing a crystal structure of a (Co. ₈₅ Al. ₁₅ ) 100- _{Y 2} O _Y film as a reference example. FIG. 2 is an observation photograph (Y = 0 to 60) of a (Co. ₈₅ Al. ₁₅ ) 100- _{Y 2} O _Y film as a reference example by a transmission electron microscope. FIG. 3 is a characteristic diagram showing a DC magnetic hysteresis curve of a Co ₆₀ Al ₁₁ O ₂₉ film as a reference example. FIG. 4 is a characteristic diagram showing the frequency characteristics of magnetic permeability of a Co ₆₀ Al ₁₁ O ₂₉ film as a reference example. FIG. 5 is a characteristic diagram showing a DC magnetic history curve of the Co ₇₀ Y ₇ O ₂₃ film. FIG. 6 is a characteristic diagram showing the frequency characteristics of the magnetic permeability of the Co ₇₀ Y ₇ O ₂₃ film. FIG. 7 is a characteristic diagram showing a DC magnetic hysteresis curve of a Co ₆₆ Sm _9.5 O _24.5 film. FIG. 8 is a characteristic diagram showing frequency characteristics of magnetic permeability of the Co ₆₆ Sm _9.5 O _24.5 film. FIG. 9 is a characteristic diagram showing the heat treatment temperature change in the magnetic field of the anisotropic magnetic field (Hk) of the Co ₆₀ Al ₁₁ O ₂₉ film as a reference example. FIG. 10 is a characteristic diagram showing the frequency characteristics of the permeability of a film obtained by subjecting a Co ₆₀ Al ₁₁ O ₂₉ film as a reference example to heat treatment in a rotating magnetic field and then heat treatment in a static magnetic field.

Claims (9)

General formula (Co _1-a Fe _a ) _100-XY M _X O _Y , where M is Dy, Er, Gd, Hf, Li, Mg, Nd, Sc, Sr, Tm, Y, Yb, Zr and Sm One or two or more elements selected from the above, the composition ratio a is a <0.3, X and Y are atomic% 6 ≦ X <12, 22 ≦ Y <37, and 30 ≦ X It has a composition of + Y <48 and a small amount of impurities, has an anisotropic magnetic field of 30 Oe to 100 Oe, an electrical resistivity of 300 μΩcm to 1500 μΩcm, and a saturation magnetic flux density of 8 kG or more. Isotropic membrane. Represented by the general formula Co ₁₀₀ - _X - _Y M _X O _Y , where M is selected from Dy, Er, Gd, Hf, Li, Mg, Nd, Sc, Sr, Tm, Y, Yb and Zr It is a seed or two or more elements, and its composition ratio x and y is 8 <x <12 in atomic%, 20 <Y <37, and 36 <x + y <48, and a small amount of impurities. A uniaxial magnetic anisotropic film having an anisotropic magnetic field of 30 Oe or more and 100 Oe or less, an electrical specific resistance value of 300 μΩcm or more and 1500 μΩcm or less, and a saturation magnetic flux density of 8 kG or more. The uniaxial magnetic anisotropic film further comprising Al as the M element. Formula _{(Co 1 -aFea) 100- X -} Y M X O Y film or _{Co 100 - X - Y M X} O in _Y film, large M element also absolute value than 1000kJ heat of formation of the size of the MO compounds The uniaxial magnetic anisotropic film according to any one of claims 1 to 3, wherein: 5. The uniaxial magnetic anisotropy according to claim 1, wherein the uniaxial magnetic anisotropy has a nano-granular structure comprising a Co phase fine particle having a particle size of 100 mm or less and a grain boundary of an oxide phase of an M element. Sex membrane. 6. The anisotropic magnetic field of the film can be controlled in a range of 30 Oe or more and 100 Oe or less by performing heat treatment in a rotating magnetic field or a static magnetic field. Uniaxial magnetic anisotropic film. 6. The uniaxial magnetic anisotropy film according to claim 1, wherein a pair of permanent magnets is disposed in the substrate holder to form a film. A transformer comprising the uniaxial magnetic anisotropic film according to any one of claims 1 to 6. An inductor comprising the uniaxial magnetic anisotropic film according to any one of claims 1 to 6.

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