JP6210401B2 - High electrical resistance ferromagnetic thin film - Google Patents

Description

  The present invention relates to a high electrical resistance thin film used for electronic device parts. In recent years, the speed of information processing and transmission in electronic devices has been rapidly increasing, and their operating frequency ranges from the conventional high frequency band (1000 MHz or less) to the quasi-microwave band (300 MHz to 3 GHz, especially the GHz band) It has increased to above (centimeter wave band, 3GHz or more). Further, in response to the multi-function and miniaturization of electronic devices, electronic components that occupy most of the internal volume have been miniaturized, and further, passive electronic components are integrated in semiconductor active electronic components. So-called on-chip development is also progressing. In such a situation where electronic components are miniaturized and integrated, high-frequency magnetic devices such as inductors, couplers, and baluns that are indispensable as electronic components are also required to be miniaturized. For this purpose, it is very effective to introduce a magnetic material into a conventional coil component.

However, the existing magnetic materials described below cannot be used because they cannot maintain sufficient characteristics up to the high frequency band.

Alloy metal materials Typical examples of these metal materials include Fe, Co, Ni, and alloys containing them. Although metal materials have very good magnetic properties as material properties, their electrical resistivity is extremely low, on the order of 1 × 10 ⁰ to 1 × 10 ¹ μohm · cm. An eddy current is generated inside the magnetic material, causing a large loss. As will be described in detail later, if these are thinned to reduce this loss, the film thickness becomes extremely thin, and the effective magnetic permeability when the device is applied is small. On the other hand, an alloy of the above magnetic metal and a noble metal such as Pd or Pt exhibits a large magnetic anisotropy. Large magnetic anisotropy is an advantageous property for obtaining a desired high-frequency material, but on the other hand, the coercive force is also large, so that it is difficult to handle as a material for signal processing electronic device parts.

Ferrite On the other hand, since ferrite is an oxide and has a high electrical resistivity, loss due to eddy current is small. However, since the saturation magnetization and anisotropic magnetic field are essentially small and the dissipation coefficient (dumping constant) of precession in the rotation of the magnetic moment is large, the resonance of the slow permeability with respect to the frequency is relatively low. Occurrence, in other words, the imaginary part of the magnetic permeability increases in the desired frequency band used, so there is a limit to low-loss utilization in the GHz band. As described above, since ferrite is unsuitable for application in the GHz band, there is no metal material other than the metal material that has sufficient magnetic characteristics particularly exceeding GHz.

Amorphous magnetic material Amorphous material has high magnetic resistivity due to containing metalloid and metal with high electrical resistivity, and has magnetic properties due to amorphous structure. Instead, high frequency magnetism has been actively researched. Some of the electrical resistivity is as large as 1 × 10 ³ μohm · cm. However, amorphous magnetic materials exhibiting such a high electrical resistivity are accompanied by a significant deterioration of the magnetic properties, so they have good high-frequency magnetic properties. In order to obtain this, materials with low electrical resistivity on the order of 1 × 10 ² μohm · cm will be used. It can be said that it does not exist.

Thin-film electronic components In order to be able to adapt existing materials to devices that operate with low loss in the frequency band targeted by this application, after thinning them, the film thickness is 3 minutes of the skin depth. Many attempts have been made to minimize eddy current loss by cutting the eddy current path by slitting the thin film, etc. However, the skin depth of the magnetic thin film with a small electrical resistivity is very shallow, so in order to reduce the eddy current loss, the film thickness must be extremely thin, specifically to the submicron order. , Significantly reducing the volume of the magnetic material. In addition, the slit processing also has problems such as a decrease in volume of the magnetic material and a local concentration of the demagnetizing field and the magnetic flux due to an unintended shape effect. Although it is not as unique as Snake's limit law in spinel ferrite, there is a trade-off relationship between the absolute value of magnetic permeability and high-frequency limit performance even in metal materials. May be relatively small, and such volume reductions and defects make the effective permeability in the magnetic circuit of the device very small. Therefore, the impedance of an electronic component with a magnetic material introduced into a conventional coil structure cannot sufficiently show a significant difference from an air core component of the same structure that does not use a magnetic material. It becomes. That is, since it is necessary to use a thick film of several to several tens of micrometers with existing materials, it is essential to improve the electrical resistivity of the magnetic material for low loss driving in a high frequency band.

In conventional nanogranular materials , electronic parts using magnetic materials have not yet been put to practical use in applications in the high frequency band (especially in the GHz band). By the way, Non-Patent Document 1: “Materia” Vol. 41, 2002 (No. 6), pp. 402 to 409, “Trends and Prospects of Nanogranular Magnetic Thin Films”, in order for the researchers of the present applicant to obtain excellent high frequency soft magnetic properties, large anisotropy is required. It explains that magnetic field (Hk), saturation magnetization (Bs) and high electrical resistivity need to be realized at the same time, and introduces research examples of oxide-based nanogranular thin films. For example, a nano-granular structure material in which a ferromagnetic metal such as Fe or Co is dispersed in a matrix made of an oxide ceramic. Nano-granular materials have a structure in which ferromagnetic granules composed of Fe, Co or their alloys in the form of nano-sized particles are dispersed in an oxide or nitride insulator. It also has a high electrical resistivity.
Subsequently, the prior art of the high electrical resistance film published in the patent document will be described.

Patent Document 1: Japanese Patent Application Laid-Open No. 2001-94175 discloses a high electrical resistivity magnetoresistive film having a large magnetoresistance effect with an MR ratio of 3% or more at room temperature and having an electrical resistivity of 10 ⁵ μohm · cm or more As proposed by the present applicant. In this film, nanometer-sized magnetic granules are dispersed in an insulator matrix made of fluoride.

Patent Document 2: Japanese Patent Application Laid-Open No. 7-86035 relates to a uniaxial magnetic anisotropic thin film which is a soft magnetic thin film having both high electric resistance and saturation magnetization and excellent in high frequency characteristics. The composition of this thin film is represented by the general formula Fe _100-xyz M _x N _y L _z (atomic%), where M is Be, B, Mg, Al, Si, Ca, Ti, Y, Zr, Mo, In, Sn, Cs, Ba, La, Hf, Ta, Bi, Pb and / or W, L is O and / or F, and each atomic ratio is 5 ≦ x ≦ 25, 0 ≦ y ≦ 15, 15 ≦ z ≦ 35, 28 ≦ x + y + z ≦ 50. The crystal structure of the thin film mainly consists of a bcc-Fe structure and an M oxide phase or fluoride phase. In the uniaxial magnetic anisotropic thin film proposed by Patent Publication 2, the maximum electric resistance value of the soft magnetic film is 1000 μohm · cm (paragraph number 0012), and the maximum frequency of the magnetic permeability of the thin film measured in the example is 500MHz.

Patent Document 3: Japanese Patent Application Laid-Open No. 9-82522 discloses a magnetic film having a uniaxial magnetic anisotropy of an appropriate size, a large electric resistance, a high saturation magnetization, and an excellent permeability and high frequency characteristics As proposed by the present applicant. The composition of the magnetic film is an oxide-based material represented by the general formula (Co _1-a Fe _a ) _100-XY M _X O _Y. M is Al, Dy, Er, Gd, Hf, Li, Mg, Nd, Sc, Sr, Tm, Y, Yb and / or Zr, the composition ratio a is a <0.3, and x and y are atomic% The composition is such that 8 <x <12, 27 <y <37, and 36 <x + y <48, and a small amount of impurities. The anisotropic magnetic field is 50 Oe or more and 100 Oe or less, the saturation magnetic flux density is 8 kG or more, and the electric resistivity is 300 μohm · cm or more and 1500 μohm · cm or less.

Patent Document 3 describes the magnetic characteristics as follows. (B) Even if the magnetic particles have a large anisotropic energy, the size is nano-sized, and the magnetization direction of each particle has different orientations due to the anisotropic energy of each particle. As a result, the entire energy of the magnetic material approaches zero and becomes soft magnetic. That is, excellent soft magnetism can be obtained by a decrease in effective magnetocrystalline anisotropy accompanying a decrease in particle size. (B) When the particle size of the granules exceeds 100 angstroms (10 nm), soft magnetism is lost. (C) When the grain boundary is thick, the magnetic interaction between the grains is lost, and the soft magnetism is also lost.
In the above (a) to (c), in order for the nano-granular material to exhibit such soft magnetism, (a) the magnetic granules approach each other at an interval that causes a magnetic interaction, and (b) It shows that the grain size of the granules needs to be smaller than the diameter that causes a reduction in effective magnetocrystalline anisotropy. On the other hand, Patent Document 3 shows that when the particle size of magnetic Co particles exceeds 100 angstroms (10 nm), perpendicular magnetic anisotropy appears and soft magnetism is lost.

In the example of Patent Document 3, the maximum value of the frequency at which the magnetic permeability of the thin film is measured is 500 MHz, and the maximum electrical resistivity achieved is 1500 μohm · cm.
Patent Document 4: Japanese Patent Laid-Open No. 2007-173863 is also an oxide-based uniaxial magnetic anisotropic film proposed by the present applicant.

Patent Document 5: Japanese Patent Application Laid-Open No. 2012-69428 relates to a thin film dielectric having a nano granular structure proposed by the present applicant. The composition of the thin film dielectric is represented by the general formula _{Fe a Co b Ni c M w} N x O y F z, M components Mg, Al, Si, Ti, Y, Zr, Nb, Hf, and / or Ta, composition ratio a, b, c, w, x, y, z is atomic ratio (%), 0 ≦ a ≦ 60, 0 ≦ b ≦ 60, 0 ≦ c ≦ 60, 10 <a + b + c <60, 10 ≦ w ≦ 50, 0 ≦ x ≦ 50, 0 ≦ y ≦ 50, 0 ≦ z ≦ 50, 20 ≦ x + y + z ≦ 70, a + b + c + w + x + y A metal granule represented by + z = 100 and made of Fe, Co and / or Ni and having a size of nm is dispersed in an insulator matrix made of M component and N, O and / or F. In addition to dielectric properties such as dielectric constant and dielectric loss, the electrical resistivity is also described as 1 × 10 ⁴ to 1 × 10 ¹⁵ μohm · cm.

Patent Document 1: Japanese Patent Application Laid-Open No. 2001-94175 Patent Document 2: Japanese Patent Application Laid-Open No. 7-86035 Patent Document 3: Japanese Patent Application Laid-Open No. 9-82522 Patent Document 4: Japanese Patent Application Laid-Open No. 2007-173863 Patent Document 5: Japanese Patent Application Laid-Open No. 2007-173863 2012-69428 gazette

  Non-Patent Document 1: “Materia” Vol. 41, 2002 (No. 6), pp. 402-409, “Trends and Prospects of Nanogranular Magnetic Thin Films”

The physical properties of nano-granular materials related to permeability in the quasi-microwave band were discussed as follows.
Electrical resistivity : Eddy current loss is proportional to frequency and inversely proportional to electrical resistivity. In order to reduce the eddy current loss in the quasi-microwave region or higher, a sufficiently higher electric resistivity than before is required. In order to increase the electrical resistivity of the nano-granular material, it is necessary that the electrical conduction is by tunnel conduction through a tunnel barrier (grain boundary) made of an insulating ceramic between the granules. For example, when the electrical resistivity is 1.5 × 10 ³ μohm · cm, the skin depth is proportional to the square root of the electrical resistivity and inversely proportional to the square root of the value obtained by multiplying the frequency and the permeability. If the permeability is 100 and the frequency is 1 GHz, it is about 6 μm, and the permeability 15 is about 6 μm at 5 GHz. Therefore, a film having a thickness of 2 μm can be used in any example. When the electrical resistivity is higher than that, a thicker film can be used. On the other hand, when the film thickness is not increased, eddy current is less likely to flow.
Ferromagnetism : The conventional thin film such as Patent Document 3 has a nano-sized magnetic metal granule having a nano-size particle size, and uses the magnetic interaction between magnetic metal granules to develop ferromagnetism. Stable permeability is achieved in the high frequency band. On the other hand, superparamagnetism, which is undesirable in Patent Document 3, is (A) separated by a distance where the magnetic metal granules do not interact with each other, and (B) the particle diameter of the magnetic metal granules is small. It must be smaller than the superparamagnetic critical particle size at room temperature. According to the study by the present inventors, the magnetic permeability of the superparamagnetic nanogranular material is extremely small, and a magnetic permeability sufficiently large for practical use cannot be obtained in the quasi-micro band.
Anisotropic magnetic field : As discussed in Non-Patent Document 1, in order to increase the magnetic resonance frequency of the magnetic permeability, it is necessary that the anisotropic magnetic field is high.
Resonance frequency of magnetic permeability : When a material has a ferromagnetic resonance, the imaginary part (loss term) of the magnetic permeability has a maximum at the resonance frequency, and shows a Gaussian distribution with this maximum as the median. It shows a certain value even around the resonance frequency. Therefore, it is said that the resonance frequency of the magnetic permeability is generally required to be twice or more of the operating frequency in order to develop a stable magnetic permeability (real part) at 300 MHz or higher with low loss. In other words, it is 600 MHz or higher, and it is particularly important to exceed 1 GHz to cope with the increase in driving frequency of the latest equipment in recent years. The resonance frequency of the magnetic permeability is proportional to the square root of the value obtained by multiplying the saturation magnetization and the anisotropic magnetic field, and becomes 1 GHz or more when the saturation magnetization is 5 kG or more and the anisotropic magnetic field is 10 Oe or more.

As described above, the above-described examination of the prior art and the researches of the present inventors are summarized as follows. A magnetic material thin film having a conventional nano-granular structure is an electronic component that is required to have a stable magnetic permeability in the GHz band as a basic characteristic. Therefore, an object of the present invention is to provide a thin film suitable for the electronic component described in the industrial application field.

The present invention solves the above problems by providing a nanogranular magnetic thin film that exhibits a very large electrical resistivity and ferromagnetism and has uniaxial anisotropy. The basic physical principle of such a magnetic thin film will be described.

  In the nano-granular structure, the above-mentioned (A) in which magnetic metal granules (hereinafter referred to as “granules”) have a magnetic interaction requires that the distance between the granules is close to that which causes an exchange interaction. However, if the granules are in contact with each other, they are magnetically coupled, but the electrical resistance is greatly reduced because the metals are in contact. Therefore, it is necessary to be electrically separated by an insulator, but at a distance between granules smaller than about 1 nm, the magnetic interaction between the granules and the tunnel of electrons through the insulator due to the quantum effect. Both conduction occurs. The electrical resistivity of a substance exhibiting electrical conduction by tunnel conduction is larger than that of metal conduction. However, since the original insulation by the insulator is greatly impaired, it is important to select a material that is particularly excellent in this original insulation. Here, nitrides and oxide insulators do not have a crystalline structure in the granular structure, even if the manufacturing method is devised, and become an amorphous structure, so the band gap is reduced to about a fraction of that of the crystalline structure. As a result, the tunneling probability of conduction electrons increases and the electrical resistivity decreases. On the other hand, the fluoride insulator can achieve high electrical resistivity even if tunnel conduction occurs at a distance of about 1 nm or less that causes magnetic coupling for the reason described later.

  Next, in order to have an effective decrease in magnetocrystalline anisotropy and a soft magnetism in the granular structure, the granules must be magnetically coupled (B). In order to satisfy this requirement (B), it is necessary to increase the total volume of granules, so that the amount of metal in the thin film increases. In this case, since the amount of the insulating ceramics is relatively reduced, the amount of the individual granules is insufficient, and the number of places where the metal granules come into contact increases, resulting in a decrease in electrical resistivity. This problem can be solved by using a fluoride insulator which will be discussed below.

A nano-granular structure made of fluoride crystals has a high electrical resistivity. This is because fluorides such as MgF ₂ and CaF ₂ have a larger band gap than oxides such as Al ₂ O ₃ (MgF ₂ : 11.8 eV, Al ₂ O ₃ : 7 to 9 eV in the crystalline state). Value), the probability that conduction electrons pass through the tunnel barrier of the nano-granular structure film is lowered, so that the electrical resistivity is increased. A feature of the nano-granular structure film using fluoride is that, unlike the case of using nitride or oxide, the fluoride has a crystal structure. The crystal structure means that the composition is stable near the stoichiometric composition, there is no decrease in the band gap unlike the material of the amorphous structure, and the metal constituting the granule at the time of manufacturing the material. Since mixing of fluorides is suppressed, it is possible to achieve high electrical resistance at a very high level compared to the conventional case. Further, by using an insulator such as this, in the metal content of the material in the region, such as electrical resistivity increased contact between granules is decreased, relatively electrical resistance as compared to conventional materials The rate is high.

The features of the present invention completed based on the above physical considerations are as follows.
First aspect is represented by the general formula _{L 100-ab M a F b} , L is at least one element selected from Fe, Co and Ni, M is Li, Be, Mg, Al, Ca, At least one element selected from Sr, Ba and Y, F is fluorine, the composition ratios a and b are atomic ratios, a is 9% or more and 50% or less, and the atomic ratio of b Is 16% or more and 60% or less, and the total atomic ratio of a + b is 25% or more and 70% or less, electric resistivity is 1.5 × 10 ³ μohm ・ cm or more, saturation magnetization is 5 kG or more, and The present invention relates to a ferromagnetic thin film having uniaxial magnetic anisotropy characterized by an anisotropic magnetic field of 10 Oe or more.

  In the second invention, the L is an alloy of one or more elements selected from Fe, Co and Ni and one or more elements selected from Pd and Pt, and the Pd, Pt in the alloy The present invention relates to a ferromagnetic thin film having uniaxial magnetic anisotropy according to the first invention, characterized in that the content of is at most 50 atomic%.

Third invention consists the L, the average particle size is 2 to 50 nm ferromagnetic fine particles, characterized by having a uniformly distributed nano-granular structure in an insulator matrix comprising a fluoride of the M and F The present invention relates to a ferromagnetic thin film having uniaxial magnetic anisotropy according to claim 1.

The fourth invention relates to a ferromagnetic thin film having uniaxial magnetic anisotropy used as a magnetic material component incorporated in a high-frequency magnetic device such as an inductor, a coupler or a balun used in the GHz band.
The present invention will be described in detail below.

  In the general formula L-MF, which represents the composition of the ferromagnetic thin film of the present invention (first invention), when the total atomic ratio of M and F is less than 25%, the contact of the granules made of metal L increases. As a result, the electrical resistivity decreases. In addition, when the total atomic ratio of M and F exceeds 70%, the distance between the granules made of the metal L is increased, so that the magnetically coupled granules are reduced and the magnetic properties of the film are lost. The M component combines with F to form an insulating ceramic. If the content of M is less than 9%, the non-stoichiometry of the insulator becomes significant, and the insulation is reduced by surplus electrons. Therefore, it is significant in the electrical resistivity when using insulators other than fluoride. There is no difference. In addition, when the amount of F exceeds 60%, F becomes extremely excessive, and this excessive F is also combined with L forming the granule to suppress the deterioration of the magnetic characteristics of the metal granule and the formation of the granule itself. Therefore, the atomic ratio of M is 9% to 50%, the atomic ratio of F is 16% to 60%, and the total atomic ratio of M and F is 25% to 70%.

FIG. 1 shows the total of M and F in the film for a thin film formed by the method described in the later-described embodiment, wherein L is made of Fe and Co, and M is Mg, Al, or Ca. The relationship between electrical resistivity and saturation magnetization is shown. It can be seen that in the composition range where the sum of M and F is 25% or more and 70% or less consistent with claim 1, both the electric resistivity of 1.5 × 10 ³ μohm · cm or more and the saturation magnetization of 5 kG or more are satisfied.

The ferromagnetic thin film of the present invention can obtain an electric resistivity of 1.5 × 10 ³ μohm · cm or more and a saturation magnetization of 5 kG or more in the above composition range. When the electrical resistivity is less than 1.5 × 10 ³ μohm · cm, eddy current loss increases and there is no advantage over conventional materials. Further, when the saturation magnetization is less than 5 kG and the anisotropic magnetic field is less than 10 Oe, the magnetic resonance has a low ferromagnetic resonance frequency, which is almost the same as that of existing ferrite, and has no advantage. In the ferromagnetic thin film of the present invention, it is necessary to simultaneously exhibit an electrical resistivity of 1.5 × 10 ³ μohm · cm or more, a saturation magnetization of 5 kG or more, and an anisotropic magnetic field of 10 Oe or more.

  In the present invention (second invention), the magnetic metal granule composed of L is made of an alloy containing a chemically very stable Pd or Pt noble metal, thereby improving the anti-fluorination property of the magnetic metal granule. Promotes phase separation with fluoride insulators. If the L element constituting the magnetic metal granule is combined with F, the saturation magnetization of the film decreases, but Pd and Pt have the effect of minimizing this. Furthermore, Pd and Pt also have the effect of significantly increasing the anisotropic magnetic field. However, since Pd and Pt are nonmagnetic metals, saturation magnetization decreases when x exceeds 50 atomic%, which is not preferable.

The nano-granular structure of the present invention (third invention) can be obtained by producing a network-like microstructured thin film composed of a magnetic metal phase and a fluoride phase by sputtering. These nano-granular films use a sputtering method, for example, an RF sputtering film forming apparatus, a magnetic metal target, for example, a disk made of Fe, Co, Ni or an alloy thereof, and a fluoride insulator target, for example, MgF ₂ , CaF _2, etc. The sintered body is simultaneously sputtered. The film formation is performed in a magnetic field or in the absence of a magnetic field, and the heat treatment after the film formation is performed for an appropriate time at each temperature in the range of 100 ° C. to 500 ° C., for example, in a static magnetic field and a rotating magnetic field or in the absence of a magnetic field. For example, the film is held for 5 minutes to 5 hours, and then these films are formed or heat-treated in a static magnetic field. An anisotropic magnetic field can be applied by any of these film forming methods and heat treatment.

In the present invention (fourth invention), a magnetic thin film having a thickness of submicron to several tens of μm is formed on a substrate of various materials and shapes, thereby making it possible to reduce the size of the magnetic component of the electronic device.
Next, a method for forming a ferromagnetic thin film according to the present invention will be described.

The ferromagnetic thin film of the present invention can be formed by a conventional sputtering device or an RF sputtering device, which is a great advantage industrially. Using a sputtering method or an RF sputtering film forming apparatus, on an alloy disc containing pure Fe, pure Co, pure Ni, or any one of Fe, Co, Ni and one or more of Pd, Pt, Use a composite target with evenly arranged tips of fluoride insulator containing M element, or apply power to metal target and insulator target at the same time, on the substrate placed facing the target When a sputter film is formed on the film, a nanogranular structure film in which magnetic granules and insulators are dispersed is obtained.
In addition, a thin film having a desired magnetic characteristic can be obtained by applying a static magnetic field during film formation to induce magnetic anisotropy and applying an anisotropic magnetic field, such as by arranging a permanent magnet near the substrate. .

  More specifically, using conventional type RF sputtering equipment, RF magnetron sputtering equipment or DC facing target sputtering equipment, pure Fe, pure Co, pure Ni or Fe, Co, Ni with a diameter of 70 to 100 mm A thin film is produced by simultaneously sputtering one or more alloy disk targets containing at least one of Pd and Pt, and a fluoride target containing M element. In sputtering film formation, pure Ar gas is used as the sputtering gas. The film thickness is controlled by adjusting the film formation time, and is formed to a thickness of about 0.3 to 30 μm. Note that the substrate is heated by indirect water cooling or at an arbitrary temperature of 100 to 800 ° C., the Ar gas pressure during film formation is 1 to 60 mTorr, and the sputtering power is 50 to 350 W. Further, a pair of permanent magnets can be arranged on the substrate holder, and a static magnetic field of 80 to 500 Oe can be applied to the substrate surface.

  In order to increase the volume ratio of the granule mentioned in paragraph 0020, it is necessary to individually control the amount of particles popping out from each of the metal target and the fluoride target. That is, assuming a thin film in which the particle size of the metal granules and polycrystalline fluoride is constant in the thin film, the power of the metal target is relatively set so that many granule components jump out of the target and deposit on the substrate. If it is increased, it becomes a ferromagnetic thin film. On the other hand, if the input power to the fluoride target is relatively increased, it becomes a superparamagnetic thin film. Therefore, the power ratio between the metal target and the fluoride target should not be greater than 1: 5. It is preferable.

  Further, the magnetic properties can be adjusted by heat treatment at 100 to 800 ° C. after film formation or during film formation. Further, the anisotropic magnetic field can be controlled by heat treatment in a static magnetic field of 10 Oe to 10 kOe or a rotating magnetic field. However, if the heat treatment temperature is less than 100 ° C., there is no effect. If the heat treatment temperature exceeds 800 ° C., the entire thin film components are completely dissolved and the structure becomes uniform, and a nano-granular structure having a hetero structure cannot be obtained.

  Further, when the film formation and heat treatment conditions are adjusted within the range of the above sputtering conditions, (1) the particle size and dispersion state of the metal granules, (2) the structure and state of the fluoride insulator, and (3) the fluoride Atomic level, including crystal structure of insulator, (4) interface between granule and fluoride insulator, (5) about several atoms in insulator and granule, and arrangement and movement of atoms at interface It has a slight effect on structural changes in

The ferromagnetic thin film of the present invention is composed of metal nano granules having ferromagnetism and a fluoride insulator grain boundary phase. The fluoride grain boundary phase exists so as to surround the ferromagnetic nanogranule, and the majority of the parts where the nanogranule does not contact each other increases the electrical resistivity. As described in detail below, it is stable in the microwave band. Magnetic permeability can be realized.
(B) Since fluoride insulators have a larger band gap than oxide insulators, the tunneling probability of conduction electrons is the nitride of conventional materials even if the granules are close enough to have a magnetic interaction. -Since it is very low compared to oxide insulators, the conductance of tunnel conduction electrons is reduced, and the electric resistivity is high. Furthermore, since the fluoride grain boundary phase has a crystal structure, the band gap does not decrease unlike conventional materials that become amorphous.
(B) Unlike conventional materials, it exhibits ferromagnetism even in a region exhibiting high electrical resistivity. FIG. 5 of Patent Document 3 proposed by the present applicant shows a magnetization curve of a Co ₇₀ Y ₇ O ₂₃ thin film in which the insulator is yttrium oxide and the metal granule is Co. In the thin film of FIG. 5, the loop of the magnetization curve in the easy magnetization direction rises vertically, and since the coercive force is almost zero, it is ferromagnetic and has uniaxial anisotropy. The resistivity is as low as 3 × 10 ² μohm · cm. In this composition system, if the amount of Co is decreased in order to increase the electrical resistivity to within the scope of this claim, ferromagnetism is lost and superparamagnetism is obtained. That is, the magnetization behavior is such that the easy magnetization direction and the difficult direction cannot be determined, and no coercive force or residual magnetization occurs. On the other hand, the magnetization curve of the thin film of the present invention is such that the total metal amount is reduced to about 57% and the electrical resistivity is on the order of 1 × 10 ⁶ μohm · cm as shown in FIG. However, the magnetization easy direction and the difficult direction can be easily discriminated, and the coercive force, the residual magnetization, and the anisotropy magnetic field are also observed from the difficult direction.
(C) Compared with the characteristics shown in Table 2 for the film of FIG. 5 of Patent Document 3 proposed by the present applicant and the film of Sample No. 22 of the present invention described later, it is read from the gradient of the magnetization characteristics in the direction of magnetization difficulty. The anisotropic magnetic field is 80 Oe in the former, 500 Oe in the latter, and the electrical resistivity is 2 × 10 ³ μohm · cm, which is about 10 times higher than the former. Since the value is maintained, it is effective for the expression of permeability characteristics suitable for practical use in the GHz range.
(D) In order to obtain stable permeability characteristics in the microwave region, the ferromagnetic resonance frequency needs to be high. In order to increase the resonant frequency, a large saturation magnetization is required simultaneously with a large anisotropic magnetic field. When comparing the characteristics shown in Table 2 with respect to the film of FIG. 5 of Patent Document 3 proposed by the present applicant and the film of Sample No. 4 of the present invention described later, the saturation magnetization is equivalent, but the former electrical resistivity is compared. Is 3 × 10 ² μohm · cm, whereas the latter is more than 100 times (5.1 × 10 ⁴ μohm · cm). In sample number 21, where the metal granule component was further increased from the sample of sample number 4, the saturation magnetization increased to 12 kG, while the electrical resistivity maintained a high value of 5.0 × 10 ³ μΩ · cm. Therefore, a practical material that exhibits stable magnetic permeability in the GHz region can be obtained.

Hereinafter, the present invention will be described in more detail with reference to examples.
[Example 1]
The preliminary test substrate is approximately 0.5 mm thick Corning # 7059 (Corning brand name) glass, about 0.5 mm thick Corning Eagle 2000 (Corning brand name) glass, 0.5 mm thick surface. Using a thermally oxidized Si wafer, 0.5 mm thick quartz glass, or similarly about 0.5 mm thick MgO, the magnetic properties of the thin film of Sample No. 7 with the film thickness varied in the range of 0.5 to 3 μm were measured. However, since the magnetic characteristics were almost the same regardless of the substrate type and film thickness, the following experiments were conducted within the following experimental conditions.

Production method and conditions of ferromagnetic thin film in Examples Film forming apparatus: RF magnetron sputtering apparatus / DC facing target sputtering apparatus Substrate: # 7059 glass, Eagle 2000 glass, quartz glass, Si wafer Film thickness: 0.3 to 10 μm
Substrate temperature: Water-cooled to 800 ° C
Sputtering pressure: 0.3-20mTorr
Sputtering power: 50-350W
Magnetic field applied to the substrate: 80 to 320 Oe
Heat treatment: Untreated or without magnetic field in vacuum at a predetermined temperature of 100 ° C to 800 ° C, held for 5 minutes to 5 hours in a static magnetic field of 10 Oe to 10 kOe or in a rotating magnetic field

Method for evaluating ferromagnetic thin film The thin film sample produced as described above was measured for its magnetization curve with a sample vibration type magnetometer (VSM), and its high-frequency permeability characteristic was measured by a shielded loop coil method. In addition, the electrical resistivity is measured using an electrical resistivity measuring device based on the direct current four-terminal method, and the film composition is measured by energy dispersive spectroscopy (EDS) or wavelength dispersive spectroscopy (WDS). analyzed. Further, the structure of the film was analyzed by an X-ray diffraction method (XRD) using Cu-Kα rays and a high-resolution transmission electron microscope (TEM). Table 1 shows the composition and temperature conditions of each thin film sample, and Table 2 shows various characteristics.

FIG. 2 shows a TEM image of sample number 5. The film has a granular structure with a nanometer (nm) order fine structure consisting of granules (blackish spherical parts) with a particle size of about 4-10 nm and insulators (white parts between granules). I understand. FIG. 3 shows the XRD pattern of sample number 6. When 2θ is around 25 ° and 52 °, a peak from the fluoride composed of AlF ₃ is observed, and when 2θ is around 44 °, a peak corresponding to the magnetic metal granules (iron, cobalt) in the film is observed and observed. . In FIG. 3, the particle size of the granule calculated from the half width of the peak of the magnetic metal granule using the Scherrer equation is 10 to 25 nm. From the above, it can be seen that these films have a nanogranular structure composed of two phases of fine nanogranule and a fluoride phase which is an insulator.

The magnetization loop of sample number 7 is shown in FIG. The two magnetization loops in the figure are measured in the easy magnetization direction and the difficult magnetization direction using VSM, and indicate that the film has uniaxial magnetic anisotropy in the film plane. The anisotropic magnetic field is 35 Oe. The anisotropic magnetic field was determined from the slope of the magnetization curve in the hard axis direction. Since the saturation magnetization is 7.5 kG, the resonance frequency of the magnetic permeability is 1.44 GHz. When the electrical resistivity of this sample was measured by the direct current four-terminal method, it showed a large value of 3.9 × 10 ⁶ μohm · cm.

FIG. 5 shows the static magnetization loop of sample number 14. This sample was heat-treated at 290 ° C. for 5 minutes by applying a magnetic field of 1 kOe in a direction of easy magnetization in a vacuum. The two magnetization loops in the figure are measured in the easy magnetization direction and the hard magnetization direction, and indicate that they have uniaxial magnetic anisotropy in the film plane. The anisotropic magnetic field determined from the inclination of the magnetization curve in the hard axis direction is 290 Oe. In addition, although the maximum magnetization appears to be about 4.5 kG in the figure, it is because the magnetization has not yet reached saturation, and when the applied magnetic field strength is further increased, a saturation magnetization value of 5.2 kG or more is shown. The resonance frequency of the permeability is 3.53 GHz. The electrical resistivity of this sample was measured by the direct current four-terminal method and found to be 2.8 × 10 ⁴ μohm · cm. The most characteristic feature of this film is that Pd is contained in the magnetic metal, so that the anisotropic magnetic field is extremely large, which greatly contributes to the increase in the frequency limit of the magnetic permeability. Similarly, in Sample No. 22 including Pd and Pt, an increase in the anisotropic magnetic field can be confirmed as compared with samples using other magnetic metals.

  FIG. 6 shows the frequency characteristics of the relative permeability of sample number 8 in the hard axis direction. This sample has a small decrease in permeability even when it exceeds 1000 MHz, and the ferromagnetic resonance frequency at which the permeability greatly decreases is around 3000 MHz, showing stable high frequency characteristics up to a band of 1 GHz (1000 MHz) or higher. . Further, FIG. 7 shows the frequency dependence of the relative permeability of sample number 9 in the hard axis direction. This sample was heat-treated at 240 ° C. for 5 hours in a vacuum 1 kOe rotating magnetic field (10 rpm). The value of magnetic permeability is as high as about 600, and maintains a substantially constant value up to a high frequency band of 1000 MHz or more, and it can be seen that it has good high frequency characteristics. These frequency characteristics are due to the fact that the ferromagnetic thin film of the present invention has high saturation magnetization, anisotropic magnetic field, and high electrical resistivity.

Comparative Example Using a 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 200 W.
It was confirmed that the structure of the resulting sample was composed of fine particles consisting of a main Co phase with a particle size of 50 angstroms or less and a network-like structure consisting of Al-O ceramic phase with a thickness of about 1 nm or grain boundaries. It was. 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, the saturation magnetization is 11 kG, the electrical resistivity is 980 μΩcm, and the magnetic properties are equivalent to the embodiment of the present invention, but the electrical resistivity is an order of magnitude lower. The result was obtained.
In order to improve the electrical resistivity, Al in the target composition was increased and the oxygen flow ratio was also increased. As a result, the magnetic properties deteriorated to such an extent that they were insufficient for the development of stable high-frequency permeability. Further, when Al and oxygen are increased, the electrical resistivity is further increased. However, in the present invention, ferromagnetism is lost even in the order of 1 × 10 ⁴ μohm · cm, which is an electrical resistivity region sufficiently exhibiting ferromagnetism, and superparamagnetism. The magnetization behavior changed to.
This is based on the premise that the volume ratio of the metal granule and the insulator is the same. If the insulator is an oxide, in this case, aluminum oxide, it has an amorphous structure, so that the electrical resistivity is low and desired. If the volume ratio of the insulator is increased in order to obtain the electrical resistivity, the distance between the metal granules becomes large and becomes superparamagnetic. In the present invention, since the insulator is fluoride, the electrical resistivity is high. Similarly, when the distance between metal granules is increased to superparamagnetism, the electrical resistivity is extremely higher than that of the conventional material. ing.

  As described above, the high electrical resistance ferromagnetic thin film according to the present invention can cope with a high frequency band covering the GHz band even if it is relatively thick, and has a characteristic having a clear significant difference from an air core component with low loss. This greatly contributes to the practical application of the on-chip high-frequency magnetic device to be realized. Although the application in the microwave region mainly in the GHz order has been described above, as can be seen from FIGS. 6 and 7, the high electrical resistance ferromagnetic film according to the present invention corresponding to the GHz band has a magnetic loss in a lower frequency band. In addition, since the eddy current loss becomes smaller, it is also effective as a device material used in, for example, the ultra high frequency band (30 to 300 MHz) and the short frequency band (3 to 30 MHz).

It is a graph which shows the electrical resistivity and saturation magnetization with respect to the total atomic% of the M component and F component of the L-MF system thin film of this invention. It is a TEM image of the sample number 5 of an Example of this invention. It is a XRD figure of the sample number 6 of an Example of this invention. It is a static magnetization loop of the sample number 7 of an Example of this invention. It is the static magnetization loop of the sample number 14 of an Example of this invention. It is a graph which shows the frequency dependence of the relative magnetic permeability of the sample number 8 of an Example of this invention. It is a graph which shows the frequency dependence of the relative magnetic permeability of the sample number 9 of an Example of this invention.

Claims (4)

Represented by the general formula _{L 100-ab M a F b} , L is at least one element selected from Fe, Co and Ni, M is Li, Be, Mg, Al, Ca, Sr, Ba and Y At least one element selected from F, F is fluorine, and the composition ratios a and b are atomic ratios, a is 9% or more and 50% or less, and b has an atomic ratio of 16% or more and 60%. %, And the total atomic ratio of a + b is 25% or more and 70% or less, electrical resistivity is 1.5 × 10 ³ μohm · cm or more, saturation magnetization is 5 kG or more, and anisotropic magnetic field A ferromagnetic thin film having uniaxial magnetic anisotropy, characterized in that is 10 Oe or more. The L is an alloy of one or more elements selected from Fe, Co and Ni and one or more elements selected from Pd and Pt, and the content of Pd and Pt in the alloy is 50 The ferromagnetic thin film having uniaxial magnetic anisotropy according to claim 1, wherein the ferromagnetic thin film has an atomic% or less. Made from the L, the average particle size is 2 to 50 nm ferromagnetic particles, claim 1 or 2, characterized in that it has uniformly distributed nano-granular structure in an insulator matrix of fluoride M and F 2. A ferromagnetic thin film having uniaxial magnetic anisotropy. The ferromagnetic thin film having uniaxial magnetic anisotropy according to any one of claims 1 to 3, which is used as a magnetic material part incorporated in an electronic device such as an inductor, a coupler, or a balun used in a GHz band.

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