JP2008127222A - Oxide magnetic material, antenna element and impedance element using the same - Google Patents

Abstract

[PROBLEMS] To realize an oxide magnetic material having a frequency (Fc) at which the loss component (μ ″) increases rapidly and having a frequency of 1 GHz or more, and to be able to be used in a frequency band of 1 GHz or more using the oxide magnetic material. An object is to provide an antenna element and an impedance element.
An oxide magnetic material mainly composed of iron oxide, cobalt oxide, and germanium oxide and having excellent electromagnetic performance in the GHz band. By using the oxide magnetic material as a magnetic core, high-frequency characteristics are achieved. An excellent magnetic element can be realized.
[Selection] Figure 1

Description

  The present invention relates to an oxide magnetic material used in various electronic devices, and an antenna element and an impedance element using the oxide magnetic material.

  Conventionally, oxide magnetic materials are spinel-type ferrites mainly composed of iron oxide, zinc oxide, nickel oxide, manganese oxide, and magnesium oxide, that is, based on Mn-Zn ferrite, Ni-Zn ferrite, and Mg ferrite. It is used in electronic circuits from low frequency circuits to around 200 MHz by adjusting the ratio and amount of subcomponents added. The magnetic elements used in these electronic circuits are various by utilizing the complex permeability μ = μ′−μ ″ × i (μ ′: permeability, μ ″: loss component) of the oxide magnetic material used for the magnetic core. It has realized the characteristic.

Furthermore, recently, hexagonal ferrites mainly composed of iron oxide, barium oxide, and strontium oxide have been used for electronic circuits in a frequency band exceeding 200 MHz (for example, see Patent Document 1).
JP-A-5-36517

  However, since the conventional oxide magnetic material has a frequency (Fc) at which the loss component (μ ″) rapidly increases is less than 1 GHz, the magnetic element using the conventional oxide magnetic material as a magnetic core can be up to 1 GHz. The use of is the limit.

  On the other hand, the progress of high frequency technology accompanying the digitization of electronic equipment using these magnetic elements has been remarkably advanced. In order to process these high-speed and large-capacity signals, it is indispensable to realize components that can cope with higher frequencies (GHz band).

  The present invention solves the above-described conventional problems, and realizes an oxide magnetic material having a frequency (Fc) at which the loss component (μ ″) increases rapidly and having a frequency of 1 GHz or more, and uses the oxide magnetic material. An object of the present invention is to provide various magnetic elements that can be used at a frequency of 1 GHz or higher.

In order to solve the above-described conventional problems, the present invention is an oxide magnetic material mainly composed of iron oxide, cobalt oxide, and germanium oxide, and the mixing ratio of iron oxide: cobalt oxide: germanium oxide Is within the composition range surrounded by 41: 51: 8 mol%, 36: 56: 8 mol%, 41:47:12 mol%, and 36:50:14 mol% in terms of Fe ₂ O ₃ , CoO, and GeO _2. .

  The oxide magnetic material of the present invention and the antenna element and impedance element using the same realize an oxide magnetic material having an electromagnetic characteristic with a frequency (Fc) at which the loss component (μ ″) increases sharply of 1 GHz or more. A magnetic element that can be used in a frequency band of 1 GHz or higher using the oxide magnetic material can be realized.

(Embodiment 1)
Hereinafter, the oxide magnetic material according to Embodiment 1 of the present invention will be described with reference to the drawings.

  FIG. 1 is a characteristic diagram showing the electromagnetic characteristics of the oxide magnetic material according to Embodiment 1 of the present invention.

Commercial iron oxide powder, germanium oxide, and cobalt oxide powder, which are starting materials for the oxide magnetic material in the first embodiment, have a composition ratio of Fe ₂ O ₃ : GeO ₂ : CoO = 38: 10: 52 mol%. The mixture was weighed and mixed, and an appropriate amount of pure water was added thereto, mixed using a ball mill, and then dried at 120 ° C. to obtain a mixed powder of starting materials.

  Next, this mixed powder was calcined at 900 ° C. and then pulverized using a disk mill until the maximum particle size became 100 μm or less to obtain a calcined ferrite powder. Appropriate amounts of an acrylic resin and a solvent as a resin binder were added to the calcined ferrite powder and pulverized and dispersed with a ball mill until the average particle size became 0.6 μm or less to obtain a ferrite slurry. Using the obtained ferrite slurry and a green sheet molding machine, a ferrite green sheet having a thickness of 100 μm was produced. Thereafter, this ferrite green sheet is pressure-bonded and laminated using a predetermined number of sheets, and the pressure-laminated ferrite green sheet is punched into a ring shape and fired at 1200 ° C. A core was obtained (Example 1). A coil having a winding number of 10 turns was produced using a copper wire having a wire diameter of 0.6 mmφ.

  Next, as a comparative example, a toroidal core having the same shape as described above was fabricated using hexagonal ferrite having substantially the same permeability at 600 MHz (Comparative Example 1). A characteristic diagram comparing the electromagnetic characteristics of the obtained toroidal cores is shown in FIG.

  As shown in FIG. 1, the frequency (Fc) at which the loss component (μ ″) increases sharply in Comparative Example 1 is around 0.8 GHz, whereas in Example 1, it is on the high frequency side near 1.8 GHz. Furthermore, since the magnetic permeability (μ ′) is maintained at about 2.5 up to around 6 GHz, it has electromagnetic characteristics that can be used as an oxide magnetic material used in a band of 1 GHz or higher. Here, as the magnetic permeability (μ ′) has a high magnetic permeability up to a high frequency band, it is more advantageous as a magnetic material for high frequency from the viewpoint of miniaturization and design.

  Next, FIG. 2 is a composition diagram for explaining the composition range of the oxide magnetic material according to Embodiment 1 of the present invention.

  The oxide magnetic materials shown in these composition diagrams are blended so that the composition ratios of the main components shown in (Table 1) are obtained by using iron oxide, germanium oxide, and cobalt oxide, respectively, using the same manufacturing process as above. A plurality of toroidal cores having the same material composition as the above were produced. The electromagnetic characteristics of the various toroidal cores thus obtained are compared (Table 1).

  From the results of (Table 1), Examples 1 to 6 have a magnetic permeability (μ ′) of 2 or more as compared with Comparative Examples 2 to 8, and at the same time, Fc is 1 GHz or more. It was found that an oxide magnetic material having excellent electromagnetic characteristics in a band of 1 GHz or higher can be obtained within the composition range indicated by the oblique line 2.

(Embodiment 2)
Hereinafter, the oxide magnetic material according to Embodiment 2 of the present invention will be described with reference to the drawings.

  FIG. 3 is a characteristic diagram showing electrical characteristics of the oxide magnetic material according to Embodiment 2 of the present invention.

As the oxide magnetic material in Embodiment 2, commercially available iron oxide powder, germanium oxide powder, cobalt oxide powder and copper oxide powder are Fe ₂ O ₃ : GeO ₂ : CoO: CuO = 38: 10: 40: 12 mol%. The mixture was weighed and blended so as to have the composition ratio, and an appropriate amount of pure water was added thereto and mixed using a ball mill, followed by drying at 120 ° C. to obtain a mixed powder. This mixed powder was calcined at 750 ° C. and then pulverized using a disk mill until the maximum particle size became 100 μm or less to obtain a ferrite calcined powder. Appropriate amounts of an acrylic resin and a solvent were added to the calcined ferrite powder as a resin van binder, and a ferrite slurry was obtained by grinding and dispersing with a ball mill until the average particle size became 0.6 μm or less. A ferrite green sheet was prepared from the obtained ferrite slurry, punched into a ring shape, and then fired at 900 ° C. to obtain a toroidal core (Example 7). The dimensional shape of the obtained toroidal core was the same as that of the first embodiment.

  On the other hand, for comparison, a toroidal core was manufactured using hexagonal ferrite having almost the same permeability at 600 MHz (Comparative Example 1). FIG. 3 shows a comparison of the electrical characteristics of the obtained toroidal cores. As shown in FIG. 3, in Comparative Example 1, the frequency (Fc) at which the loss component (μ ″) increases rapidly is around 0.8 GHz, whereas in Example 7, the high frequency side around 1.3 GHz is used. It can be seen that the magnetic permeability (μ ′) is maintained at about 2.4 up to around 6 GHz.

  In addition, since this material composition contains CuO, low temperature sintering is possible. For example, an oxide that can be simultaneously sintered with a conductive material such as Ag or Cu having a melting point of about 900 ° C. and excellent in conductivity. A magnetic material can be realized.

  As described above, an oxide magnetic material having an electromagnetic property that can be fired at a firing temperature of about 900 ° C. and can be used in a band of 1 GHz or more is a laminated device having an inner layer electrode such as Ag or Cu. Can be used.

  Next, the material composition of the oxide magnetic material will be described.

Like the above, commercial iron oxide powder, a germanium oxide powder and cobalt oxide powder _{Fe 2 O 3: GeO 2:} CoO = 38: 10: against 52 mol% composition ratio, the CoO in CuO 6, 8, A toroidal core having the same size and shape as described above was produced using an oxide magnetic material having a material composition substituted at a ratio of 10, 12, 14, 16, 18 mol%. The firing density and electromagnetic properties of these toroidal cores are shown in Table 2.

  From the results of (Table 2), when the substitution amount of CuO was 6 mol%, a sufficient firing density was not obtained and the magnetic permeability was 2 or less. Further, a sufficient firing density is obtained at 8 mol% or more, but at 18 mol%, the frequency (Fc) at which the loss component (μ ″) rises rapidly is 1 GHz or less, and the substitution of excess CuO deteriorates the frequency characteristics. Therefore, the optimal substitution amount of CuO is desirably 8 to 16 mol%.

  Moreover, the same result was able to be obtained even if it replaced CoO with CuO similarly to the composition range of Embodiment 1.

The same effect can be obtained regardless of whether the oxide as the main component material or the added subcomponent is an oxide or carbonate having a different valence, such as CoO, Co ₂ O ₃ , Co ₃ O _4, or CoCO _3. Is confirmed to be obtained.

(Embodiment 3)
Hereinafter, an antenna element which is one of the magnetic elements according to Embodiment 3 of the present invention will be described with reference to the drawings.

  FIG. 4 is a perspective view of a ferrite core used for an antenna element which is one of magnetic elements according to Embodiment 3 of the present invention, and FIG. 5 is a part for explaining the structure of the antenna element using the ferrite core. It is a notch perspective view.

  4 and 5, reference numeral 13 denotes a ferrite core made of an oxide magnetic material. A conductor coil 14 made of copper or silver is formed on the surface of the ferrite core 13, and an insulator layer 15 made of resin or the like is formed on the surface of the conductor coil 14 to constitute an antenna element. is there. The manufacturing method of the antenna element configured as described above will be described below.

  The oxide magnetic material having the composition in the first embodiment is formed as a rod-shaped ferrite core and then fired at 1200 to 1300 ° C. Then, the ferrite core 13 of the antenna element which has a shape of diameter: 8mm and height: 10-12mm was obtained by cutting into the shape shown in FIG.

  Next, a metal having a low resistance such as copper or silver is formed on the entire surface of the ferrite core 13 by a plating method or the like, and then a laser cut is performed in a spiral shape to form a conductor coil 14 having two to three turns. Formed.

  Thereafter, the ferrite core 13 on which the conductor coil 14 was formed was resin-molded to form an insulator layer 15, thereby completing the antenna element shown in FIG. 5 (Example 12).

  For comparison, a resin core having a similar shape was produced in order to match the resonance frequency of the antenna element, and an antenna element (Comparative Example 12) was produced by the same method as described above.

  Further, an antenna element (Comparative Example 13) using hexagonal ferrite as the ferrite core 13 having the same shape was produced.

  The resonance frequency and radiation characteristics of each obtained antenna element were measured. For this measurement, radiated power is measured. This radiated power was measured by the following method. In the anechoic chamber, power is supplied from the signal generator to the evaluation sample, and the radiated radio wave is received by the specified antenna in all directions while being analyzed by the spectrum analyzer, and the measured value is compared with the standard dipole antenna. The radiation efficiency was measured by As a result of the measurement, the radiation loss was -1.7 dB in Example 12, and it was confirmed that the performance was actually usable in the 2 GHz band.

  From the above results, in order to have a resonance frequency in a band of GHz or higher and satisfy the radiation loss, when the size of the antenna element of Comparative Example 12 is 100, the antenna element using Example 12 has a volume ratio. Therefore, it was found that the antenna element used in the GHz band is effective for downsizing.

  Further, the antenna element having hexagonal ferrite as the ferrite core 13 has a large radiation loss, and the size of the antenna element used in the GHz band cannot be designed accurately.

  It has been confirmed that the same effect can be obtained in the composition range of the second embodiment of the ferrite core.

  Further, the antenna element may be connected to the electric circuit by soldering or caulking, but it is more preferable because the connection strength can be ensured by making the connecting portion into a screw shape. In addition to the cutting method, this screw shape may be a powder press method using a split mold.

  In addition, Ag, Cu, Au, Al, Ni, Pt, Pd, etc. are used for metal plating, but Ag and Cu having a particularly high conductivity are more desirable.

  The conductor coil 14 may be formed by a method of winding a wire or a method of punching a metal sheet metal into a coil, and the same effect can be obtained.

  A thin nonmagnetic material film may be formed between the surface of the ferrite core 13 and the conductor coil 14.

  The antenna element may be covered with a resin mold or a cap of a resin molded product.

  Further, since the wavelength shortening effect due to the magnetic permeability (μ ′) is used, it goes without saying that the same effect can be obtained not only for the helical type antenna element but also for an antenna element such as a patch antenna. Nor.

  As described above, the antenna element includes a ferrite core, a conductor coil spirally wound around the core, and an insulator layer covering the conductor coil. By using the antenna element using the oxide magnetic material described in Embodiment 2, a small antenna element having excellent characteristics at 1 to 3 GHz can be realized.

(Embodiment 4)
Hereinafter, an impedance element which is one of magnetic elements according to Embodiment 4 of the present invention will be described with reference to the drawings.

  6 is a laminated structure diagram of an impedance element which is one of magnetic elements according to Embodiment 4 of the present invention, and FIG. 7 is a perspective view of the impedance element.

  6 and 7, reference numeral 5 denotes a conductor such as silver or a silver alloy. The oxide magnetic material 6 is formed by laminating ferrite green sheets of an oxide magnetic material with the conductor 5 sandwiched between the upper and lower sides. . This oxide magnetic material 6 is an insulator. Two external electrodes 7 connected to both ends of the conductor 5 formed inside are formed on both ends of the oxide magnetic material 6 to constitute an impedance element. Thus, the impedance element used as a noise countermeasure component is realized by covering the conductor 5 which is a signal line with the oxide magnetic material 6. Since the frequency (Fc) at which the loss component (μ ″) of the oxide magnetic material 6 increases abruptly is set as a cutoff frequency, the impedance value of the impedance element is selectively increased at a frequency higher than the cutoff frequency. In this case, the larger the magnetic permeability (μ ′) of the oxide magnetic material 6, the larger the impedance value can be designed and the more excellent the impedance element.

  A method for manufacturing the impedance element configured as described above will be described below.

  A ferrite calcined powder of the oxide magnetic material described in the second embodiment was produced, and an appropriate amount of butyral resin and butyl acetate was added to the calcined ferrite powder and sufficiently dispersed using a ball mill to obtain a ferrite slurry. A ferrite green sheet was obtained from this ferrite slurry by a doctor blade method. A pattern of the conductor 5 was printed on the ferrite green sheet using an Ag paste. A plurality of ferrite green sheets on which the pattern of the conductor 5 is printed and a ferrite green sheet on which the conductor 5 is not printed are stacked so as to have a desired thickness, and then cut into individual pieces to form a chip-shaped molded product. Obtained. By firing this molded article at 880 to 920 ° C., a sintered body of an oxide magnetic material having the conductor 5 formed in the inner layer was obtained. An impedance element shown in FIG. 6 can be completed by forming two external electrodes 7 connected to both ends of the conductor 5 at both ends of the sintered body of the oxide magnetic material (Example 13). This impedance element is an impedance element having a chip shape of length: 1.60 mm, width: 0.80 mm, and height: 0.80 mm.

  For comparison, an impedance element was fabricated using hexagonal ferrite (Comparative Example 14).

  The cut-off frequency (= frequency at which the impedance becomes 10Ω) in Comparative Example 14 is 0.8 GHz, and in Example 13, it is shifted to a higher frequency side to 1.5 GHz, which can be used as a noise filter for the GHz band. It can be seen that the impedance element can be used. The result of this characteristic comparison is shown in FIG.

  Note that the Ag pattern of the conductor coil 5 formed in the inner layer portion may be other than the meander shape, and the coil may be formed in a spiral shape by laminating ferrite green sheets through vias. In that case, if the distance between the end of the spiral conductor coil 5 and the external electrode 7 is short, the impedance value decreases, so it is desirable to make this interval wide, and it is more preferable to set this interval to 200 μm or more. preferable.

  In addition, even in a magnetic element including two coils such as a common mode noise filter, by providing the oxide magnetic material of the present invention around the embedded coil, the inductance does not increase remarkably below the Fc frequency. Since the value can be increased, it is effective in improving the magnetic coupling.

  The material for forming the conductor coil 5 may be Ag or an Ag alloy, but Ag is preferable for increasing the electrical conductivity.

  As described above, the impedance element includes a magnetic insulator, a conductor coil provided inside the magnetic insulator, and two external electrodes connected to the conductor coil. By making the impedance element using the oxide magnetic material described in the second embodiment, the cut-off frequency of the low-pass filter can be made 1 GHz band or more, and the noise is efficiently cut because it has a large impedance value. A small impedance element that can be used in a GHz band that can be realized can be realized.

  As described above, the oxide magnetic material according to the present invention and the antenna element and impedance element using the oxide magnetic material are useful as an electronic component in an electronic device used in a band of 1 GHz or higher.

Characteristics diagram of oxide magnetic material according to Embodiment 1 of the present invention Composition diagram showing the same composition range Characteristic diagram of oxide magnetic material in Embodiment 2 of the present invention External view of ferrite core in Embodiment 3 of the present invention Partial cutaway perspective view of the antenna element Structure diagram of lamination of impedance elements in embodiment 4 of the present invention Perspective view of the impedance element Comparison chart of characteristics

Explanation of symbols

5 Conductor 6 Oxide Magnetic Material 7 External Electrode 13 Ferrite Core 14 Conductor Coil 15 Insulator Layer

Claims (5)

An oxide magnetic material mainly composed of iron oxide, cobalt oxide, and germanium oxide, wherein the mixing ratio of iron oxide: cobalt oxide: germanium oxide is 41:51 in terms of Fe ₂ O ₃ , CoO, and GeO _2. 8, 36: 56: 8, 41:47:12, oxide magnetic material in a composition range surrounded by 36:50:14 mol%. The oxide magnetic material according to claim 1, wherein CoO is substituted with 10 to 16 mol% of CuO. An antenna element comprising a ferrite core, a conductor coil spirally wound around the core, and an insulator layer covering the conductor coil. The ferrite core includes iron oxide, cobalt oxide, and germanium oxide as main components. The compounding ratio of iron oxide: cobalt oxide: germanium oxide is 41: 51: 8 mol%, 36: 56: 8 mol%, 41:47 in terms of Fe ₂ O ₃ , CoO, GeO _2. : An antenna element using an oxide magnetic material in a composition range surrounded by 12 mol% and 36:50:14 mol%. The antenna element according to claim 3, wherein CoO is substituted with 10 to 16 mol% of CuO. An impedance element including a magnetic insulator, a conductor coil provided in a meander shape inside the magnetic insulator, and two external electrodes connected to the conductor coil. As the magnetic insulator, iron oxide and , An oxide magnetic material mainly composed of cobalt oxide and germanium oxide, wherein the mixing ratio of iron oxide: cobalt oxide: germanium oxide is 41: 51: 8 mol% in terms of Fe ₂ O ₃ , CoO, GeO ₂ , An impedance element using an oxide magnetic material having a composition range surrounded by 36: 56: 8 mol%, 41:47:12 mol%, and 36:50:14 mol%, in which CoO is substituted by 10 to 16 mol% with CuO.

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