JP2005093527A - Soft magnetism thin film for high frequency and magnetic element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a soft magnetism thin film which is easy for film formation because of a single layer film, and exhibits a superior soft magnetism property in a high frequency band of a GHz region. <P>SOLUTION: The soft magnetism thin film comprises a compound organization which includes a ferromagetic Fe crystal grain which contains C of 10-35 at%, and has a composition in which a remaining portion is substantially composed of Fe and whose average grain diameter is at most 20nm, and a ferromangetic amorphous phase occupying 30-75 vol%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a high-frequency soft magnetic thin film having high saturation magnetization and high permeability characteristics in a high-frequency band.

With the miniaturization and high performance of magnetic elements, a soft magnetic thin film material having high saturation magnetization and high permeability in a high frequency band of GHz (hereinafter referred to as GHz band) is required.
For example, a monolithic microwave integrated circuit (MMIC), which is in increasing demand mainly for wireless transceivers and portable information terminals, has an active element such as a transistor, a line, a resistor, a semiconductor substrate such as Si, GaAs, and InP. This is a high-frequency integrated circuit configured by collectively and integrally manufacturing passive elements such as capacitors and inductors.

  In such an MMIC, passive elements, particularly inductors and capacitors occupy a larger area than active elements. Such occupation of the large area of the passive element results in a large consumption of an expensive semiconductor substrate, that is, an increase in cost of the MMIC. Therefore, in order to reduce the chip area and reduce the manufacturing cost of the MMIC, it is a problem to reduce the area occupied by the passive elements.

  A planar spiral coil is often used as an MMIC inductor. There has already been proposed a method of increasing the inductance by inserting soft magnetic thin films on the upper and lower surfaces or one surface of the spiral coil (in other words, a method for obtaining a conventional inductance even with a small occupied area) (for example, non-patented). Reference 1 (J. Appl. Phys. 85, 7919 (1999))).

However, in order to apply a soft magnetic material to an MMIC inductor, first, it is required to develop a soft magnetic thin film having high permeability in the GHz band and low loss. Furthermore, a large specific resistance is also required to reduce eddy current loss.
Further, in such an MMIC, since the distance between each element is close to several hundred μm, electromagnetic wave noise is easily induced. As a countermeasure, the magnetic permeability is high in the GHz band, and in particular, a loss component (permeability of magnetic permeability). Applications of high-frequency thin films having a large imaginary part μ ″) have been proposed (for example, Patent Document 1 (Japanese Patent Laid-Open No. 2001-210518), Patent Document 2 (Japanese Patent Laid-Open No. 2002-158486)).

  Conventionally, alloys having Fe or FeCo as a main component are well known as soft magnetic materials having high saturation magnetization. However, when a soft magnetic thin film made of an Fe-based or FeCo-based alloy is produced by a film forming technique such as sputtering, the film has a high saturation magnetization, but the coercive force increases and it is difficult to obtain good high frequency characteristics. there were.

On the other hand, Co-based amorphous alloys are known as materials having excellent soft magnetic properties. This Co-based amorphous alloy is mainly composed of amorphous material containing one or more elements selected from Y, Ti, Zr, Hf, Nb, Ta, etc., with Co as a main component. . However, when a soft magnetic thin film made of a Co-based amorphous alloy having a zero magnetostrictive composition is produced by a film forming technique such as sputtering, the magnetic permeability of the film is large, but the saturation magnetization is about 11 kG (1.1 T), and Fe Small compared to the system. Furthermore, since the loss component (imaginary part μ ″ of the magnetic permeability) becomes large after the frequency of about 100 MHz and beyond this, it cannot be said that it is suitable as a soft magnetic material used in the GHz band.

In order to realize an inductor that can be used in the GHz band, an attempt has been made to increase the resonance frequency by converting the soft magnetic thin film made of the above materials into a microwire and increasing the shape anisotropy energy. (For example, Non-Patent Document 4 (Journal of Applied Magnetics Society of Japan, 24,879 (2000))). However, this method not only complicates the process, but also has a problem that the effective magnetic permeability of the soft magnetic thin film is lowered.

  Under such circumstances, various proposals have heretofore been made in order to improve the high-frequency characteristics of soft magnetic thin films. The basic policy of the improvement is to suppress eddy current loss or increase the resonance frequency. Specific measures for suppressing eddy current loss include, for example, multilayering by lamination with a magnetic layer / insulating layer (high resistance layer) (for example, Patent Document 3 (Japanese Patent Laid-Open No. 7-249516)), metal -Granularization of nonmetals (oxides, fluorides) (for example, Non-Patent Document 2 (J. Appl. Phys. 79, 5130 (1996))) and the like have been proposed. However, in these methods, since a high-resistance nonmagnetic phase is inserted, there arises a problem that saturation magnetization is lowered. Further, in order to use these granular thin films as a countermeasure for electromagnetic wave noise, it is preferable that the magnetic permeability is high in the GHz band, and in particular, the loss component (the imaginary part μ ″ of the magnetic permeability) is large. In the case of a thin film in an as-depo.state, a high magnetic permeability characteristic cannot be obtained because stress exists in the film, and heat treatment must be performed after the film formation.

On the other hand, studies on highly saturated magnetic thin films using multilayer films in which soft magnetic layers and highly saturated magnetic layers are alternately laminated are also being conducted. That is, CoZr / Fe (Non-Patent Document 5 (Journal of Applied Magnetics Society of Japan, 16, 285 (1992))), FeBN / FeN (Patent Document 4 (JP-A-5-101930)), FeCrB / Fe (Non-patent) Ref. 3 (J. Appl. Phys. 67, 5131 (1990))), Fe-Hf-C / Fe (Non-Patent Document 6 (Journal of Applied Magnetics Society of Japan, 15, 403 (1991))) Examples have been reported. All of these are effective in increasing the saturation magnetization. However, in these techniques, since it is necessary to laminate | stack the film | membrane of a different composition, the preparation is complicated.
On the other hand, Fe-C thin films have been studied as soft magnetic thin films having high saturation magnetization. Conventionally, a thin film mainly composed of Fe and C has been developed for forming a magnetic pole of a thin film magnetic head because of its soft magnetism and high saturation magnetization. As a method for producing this thin film represented by Fe-M-C (where M = Ti, Cr, Hf, V, Nb, Ta, Cr, Mo, W, etc.), as-depo. A method is known in which an MC compound is precipitated at a grain boundary by performing a heat treatment at a high temperature after film formation so as to have an amorphous structure as a whole in a state (for example, patents). Document 5 (Japanese Patent Laid-Open No. 4-139805), Non-Patent Document 7 (Journal of Applied Magnetics Society of Japan, 14, 319 (1990))). The Fe-MC thin film produced by this method has a complicated composition and has a problem of requiring a heat treatment step.
Recently, a technique for epitaxially growing an Fe—C thin film containing 4 to 8 at% of C on a single crystal substrate has been developed (for example, Non-Patent Document 8 (IEEE Trans. Mag., 37, 2179 (2001)). ), This method has a cost problem such as using an expensive single crystal substrate.
Further, a soft magnetic thin film having an amorphous structure is developed by increasing the C content to 25 at% or more (for example, Non-Patent Document 9 (Trans. Mag. Soc. Japan, 2, 15 (2001)). )). The Fe—C thin film obtained by this method contains a large amount of C in order to obtain an amorphous structure, and there is a problem that saturation magnetization is lowered.
Thus, conventionally developed Fe-C thin films have a single crystal, microcrystal, or amorphous form, and have been mainly applied to write heads or perpendicular recording media for hard disks. It was.

JP 2001-210518 A JP 2002-158486 A JP-A-7-249516 JP-A-5-101930 Japanese Patent Laid-Open No. 4-139805 J. Appl. Phys. 85, 7919 (1999) J. Appl. Phys. 79, 5130 (1996) J. Appl. Phys. 67, 5131 (1990) Journal of the Japan Society of Applied Magnetics, 24, 879 (2000) Journal of Japan Society of Applied Magnetics, 16, 285 (1992) Journal of the Japan Society of Applied Magnetics, 15, 403 (1991) Journal of the Japan Society of Applied Magnetics, 14, 319 (1990) IEEE Trans. Mag., 37, 2179 (2001) Trans. Mag. Soc. Japan, 2, 15 (2001)

  The present invention has been made on the basis of such a technical problem, and is an as-depo. It is an object of the present invention to provide a soft magnetic thin film that can be easily used in a state and that exhibits high permeability characteristics in the GHz band. It is another object of the present invention to provide a thin film having a large permeability loss portion (μ ″) and a wide bandwidth in the GHz band.

The present invention has a composition containing 10 to 35 at% of C, the balance being substantially made of Fe, an average grain diameter of 20 nm or less of ferromagnetic Fe crystal grains, and a ferromagnetic amorphous phase occupying 30 to 75 volume%, The above-mentioned problems have been solved by a high-frequency soft magnetic thin film comprising a composite structure containing
According to the high-frequency soft magnetic thin film of the present invention, the following characteristics can be provided.
Saturation magnetization (Bs): 1.8 T or more, desirably 2.0 T or more Coercive force (coercivity (Hce) in the easy axis direction and coercivity (Hch) in the hard axis direction): 5 Oe or less, desirably 3 Oe or less Real part (μ ′) of complex permeability at 1 GHz: 200 or more, desirably 400 or more Resonance frequency: 1 GHz or more, desirably 2 GHz or more The imaginary part (μ ″) of complex permeability is the maximum value of μ ″ max (μ ”) ) 50% of the frequency band normalized to the center frequency (B50): 100% or more, desirably 120% or more, specific resistance: 60 μΩcm or more, desirably 100 μΩcm or more

  The high-frequency soft magnetic thin film of the present invention can be used as a component of a magnetic element. The high-frequency soft magnetic thin film constituting the magnetic element includes 10 to 35 at% of C, the balance being substantially composed of Fe, and ferromagnetic Fe crystal grains having an average grain size of 20 nm or less; It consists of a composite structure containing a ferromagnetic amorphous phase occupying 70% by volume.

  According to the present invention, it is possible to provide a high-frequency soft magnetic thin film that exhibits high permeability characteristics in the GHz band without laminating a plurality of thin films having different compositions. Further, according to the present invention, it is possible to provide a thin film having a large permeability loss portion (μ ″) and a wide bandwidth in the GHz band.

The high-frequency soft magnetic thin film of the present invention contains Fe and C, and the C content is in the range of 10 to 35 at%. If it is less than 10 at%, it is difficult to produce a predetermined amount of amorphous phase, while if it exceeds 35 at%, the proportion of the amorphous phase is excessive. A desirable C content is 12 to 30 at%, and a more desirable C content is 15 to 25 at%.
The high-frequency soft magnetic thin film of the present invention is composed of a composite structure including ferromagnetic Fe crystal grains having an average grain size of 20 nm or less and a ferromagnetic amorphous phase occupying 30 to 75% by volume. The high-frequency soft magnetic thin film of the present invention having such a composite structure has excellent soft magnetic properties in the GHz band.
If the average grain size of the ferromagnetic Fe crystal grains exceeds 20 nm, the soft magnetic characteristics at high frequencies are deteriorated. The average grain size of the ferromagnetic Fe crystal grains is preferably 15 nm or less, more preferably 10 nm or less.

In the high-frequency soft magnetic thin film of the present invention, the amorphous phase occupies 30 to 75% by volume of the tissue. This is because if the amorphous phase is less than 30% by volume, the coercive force increases and the permeability decreases. Moreover, B50 and specific resistance are also small values. Further, when the amorphous phase exceeds 75% by volume, the saturation magnetization becomes small, and B50 becomes small. Therefore, the amorphous phase occupies 30 to 75% by volume of the structure. The amorphous phase is desirably 35 to 70% by volume, more desirably 40 to 65% by volume.
The high-frequency soft magnetic thin film of the present invention is desirably used with a film thickness of 100 to 2000 nm. If it is less than 100 nm, for example, when applied to a planar magnetic element, there arises a disadvantage that it becomes impossible to handle desired power. On the other hand, when the thickness exceeds 2000 nm, the film formation time becomes long, and the productivity is deteriorated. A desirable film thickness is 100 to 1000 nm, and a more desirable film thickness is 200 to 500 nm.

The high-frequency soft magnetic thin film of the present invention is formed on a substrate. Examples of the substrate include a glass substrate, a ceramic material substrate, a semiconductor substrate, and a resin substrate. Examples of the ceramic material include alumina, zirconia, silicon carbide, silicon nitride, aluminum nitride, steatite, mullite, cordierite, forsterite, spinel, and ferrite.
The high-frequency soft magnetic thin film according to the present invention adopts the above composition and structure, and exhibits excellent soft magnetic characteristics as described above in the as-deposited state on the substrate. Can do. Therefore, the high-frequency soft magnetic thin film according to the present invention can be applied to high-frequency planar magnetic elements such as thin-film inductors and thin-film transformers, or soft magnetic thin films and inductors used in monolithic microwave integrated circuits (MMICs). The present invention can be applied not only to an active element that operates at high speed, a high-frequency electronic component, and an electromagnetic wave absorber that suppresses unnecessary radiation, which is a problem in electronic devices.

The high-frequency soft magnetic thin film of the present invention can be produced by sputtering. More specifically, RF sputtering, DC sputtering, magnetron sputtering, ion beam sputtering, inductively coupled RF plasma assisted sputtering, facing target sputtering, and the like are used.
As a target for forming the high-frequency soft magnetic thin film of the present invention, a composite target in which C pellets are arranged on an Fe target may be used, or an alloy target of Fe and C may be used.
Here, when the composition is constant, the volume occupied by the amorphous phase increases as the input power during sputtering film formation (simply referred to as sputtering power) decreases. On the contrary, the larger the sputtering power, the smaller the occupied volume of the amorphous phase, and the soft magnetic characteristics are improved. That is, the structure of the high-frequency soft magnetic thin film according to the present invention is not determined only by the C content but also varies depending on the film forming conditions. Even when the sputtering power is low, excellent soft magnetic characteristics can be obtained by applying a bias voltage to the deposition substrate. The bias voltage is desirably applied when the sputtering power becomes 0.5 W / cm ² or less. The voltage in that case is 10
It is desirable to set it to 0V or more.

Next, an example in which the high-frequency soft magnetic thin film of the present invention is applied to a planar inductor will be described with reference to FIGS. In addition, this application example is an example to the last, and it cannot be overemphasized that the application range of the soft magnetic thin film for high frequencies of this invention is not limited. 6 is a diagram schematically showing a plane of the inductor, and FIG. 7 is a diagram schematically showing a cross section taken along the line AA of FIG.
An inductor 10 shown in these drawings is formed so as to cover a substrate 11, planar coils 12, 12 formed spirally on both front and back surfaces of the substrate 11, and the planar coils 12, 12 and the substrate 11 surface. And a pair of high-frequency soft magnetic thin films 1 formed so as to cover the insulating films 13 and 13. The high-frequency soft magnetic thin film 1 according to the present invention is used as the high-frequency soft magnetic thin film 1. The two planar coils 12 and 12 are electrically connected through a through hole 15 formed in a substantially central portion of the substrate 11. Further, terminals 16 for connection are drawn out of the substrate 11 from the planar coils 12 and 12 on both sides of the substrate 11. Since such an inductor 10 is configured such that the planar coils 12 and 12 are sandwiched between the pair of high-frequency soft magnetic thin films 1 via the insulating films 13 and 13, the inductor 10 is connected between the connection terminals 16 and 16. It is formed.
The inductor 10 formed in this way is small, thin and light, and exhibits excellent inductance particularly in the GHz band. In the inductor 10 described above, a transformer can be formed by providing a plurality of planar coils 12 and 12 in parallel.

Specific examples of the high-frequency soft magnetic thin film of the present invention will be described below.
Fe-C thin films were prepared under the conditions shown in Table 1 using an opposed target sputtering apparatus. As the target, a composite target in which a C (carbon) chip was arranged on a pure Fe target was used. A fused silica glass of 10 mm × 10 mm × 0.5 mm was used as a substrate for forming a thin film, and film formation was performed in an Ar atmosphere at room temperature so that the film thickness was about 500 nm.
Sample No. The results of Mossbauer analysis performed on the thin films 1, 2 and 6 are shown in FIGS. As shown in FIG. 1 and FIG. The thin films 1 and 2 are composed of Fe crystal grains and an amorphous phase. 1 is 42%, sample no. 2 was confirmed to be 64%. On the other hand, as shown in FIG. It was confirmed that the thin film 6 was almost composed of Fe crystal grains, and the volume fraction of the amorphous phase was only 10%.
The obtained thin film was measured for the volume fraction of the amorphous phase, the C content, and the average particle diameter of crystals present in the thin film. The obtained thin film was measured for magnetic characteristics, frequency characteristics of permeability and specific resistance. The results are shown in Table 1. Sample No. For 1 and 6, the frequency characteristics of the magnetic permeability are shown in FIGS.

As shown in Table 1 (FIG. 4), the high-frequency soft magnetic thin film (sample Nos. 1 to 5) according to the present invention has a saturation magnetization (Bs) of 1.9 T or more and an easy magnetization axis direction. The coercive force (Hce) and the coercive force (Hch) in the hard axis direction are values of 5 Oe or less. Moreover, the high-frequency soft magnetic thin film (sample Nos. 1 to 5) according to the present invention has a high permeability (μ ′) of 200 or more, and the resonance frequency (fr) is 1 GHz or more. Furthermore, the specific resistance is 60 μΩcm or more, and in addition, B50 is 100% or more.
In contrast to the sample No. 1 with an amorphous phase of 10% by volume. No. 6 has a coercive force exceeding 10, and the value of B50 is also small. Sample No. 100% of the amorphous phase was used. 7 shows that saturation magnetization (Bs) and B50 are small.

Sample No. It is a figure which shows the result of the Mossbauer analysis performed about 1 thin film. Sample No. It is a figure which shows the result of the Mossbauer analysis performed about 2 thin films. Sample No. FIG. 6 is a diagram showing the results of Mossbauer analysis performed on the thin film 6. Sample No. 4 is a graph showing frequency characteristics of magnetic permeability of a thin film 1. Sample No. 6 is a graph showing frequency characteristics of magnetic permeability of a thin film 6. It is a top view which shows an example of the inductor to which the soft magnetic thin film for high frequencies of this invention was applied. It is AA arrow sectional drawing of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Soft magnetic thin film for high frequencies, 11 ... Board | substrate, 12 ... Planar coil, 13 ... Insulating film, 10 ... Inductor

Claims (2)

Containing 10 to 35 at% of C, the balance being substantially composed of Fe,
A soft magnetic thin film for high frequency, comprising a composite structure including ferromagnetic Fe crystal grains having an average grain size of 20 nm or less and a ferromagnetic amorphous phase occupying 30 to 75% by volume. A magnetic element having a soft magnetic thin film for high frequency,
The high-frequency soft magnetic thin film is
Containing 10 to 35 at% of C, the balance being substantially composed of Fe,
A magnetic element comprising a composite structure including ferromagnetic Fe crystal grains having an average grain size of 20 nm or less and a ferromagnetic amorphous phase occupying 30 to 75% by volume.

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