Compositions – Magnetic – Iron-oxygen compound containing
Reexamination Certificate
2002-03-12
2003-12-09
Koslow, C. Melissa (Department: 1755)
Compositions
Magnetic
Iron-oxygen compound containing
C252S062630, C428S469000, C428S689000, C428S699000, C428S697000
Reexamination Certificate
active
06660179
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a sintered body used in a high-frequency circuit component and a high-frequency circuit component using the sintered body.
BACKGROUND ART
(1) In recent years, along with a size reduction in electronic equipment and a movement toward higher-frequency electronic equipment, demand for an electronic part having a high inductance and a high impedance in a high-frequency band has been increasing. To obtain a compact electronic part having a high inductance and a high impedance, it is desirable to prepare a coil having the multilayer structure that a conductive body is incorporated into a magnetic material by a so-called printing method or sheeting method.
The number of turns of the coil can be increased due to the multilayer structure and the structure is a closed magnetic circuit, so that a high inductance and a high impedance can be obtained.
As a conductive body to be incorporated into a sintered body, in general, silver (Ag) is often used in consideration of electric resistivity, a melting point and costs. Since the melting point of silver is not higher than 1,000° C., an NiZn-based ferrite which exhibits a high sintered density even when based at 900° C. has heretofore been generally used as a magnetic material for the multilayer structure.
However, since the NiZn-based ferrite has low magnetic anisotropy, it causes natural resonance at frequencies of several hundred megahertz, so that it cannot be used within a frequency band of gigahertz.
Although an air-core coil using a non-magnetic material is sometimes used as a high-frequency specification, use of the non-magnetic material makes it difficult to obtain a high inductance and a high impedance.
Meanwhile, a hexagonal ferrite hardly causes natural resonance and has high permeability even within a frequency band of gigahertz since the magnetic anisotropy in the in-plane direction of a hexagonal plate crystal is different from that in the direction perpendicular to the in-plane direction. However, in the case of the hexagonal ferrite, the firing temperature must be high in order to obtain desired sintered density and magnetic properties.
Although it has heretofore been attempted to sinter a hexagonal ferrite at a temperature lower than or equal to the melting point of Ag by using a low-melting-point oxide in the hexagonal ferrite, the yield of soft magnetic phase is low, and it is difficult to cause the magnetic properties of the hexagonal ferrite to be fully exhibited.
One of the prior arts related and similar to the present invention is Japanese Patent Application Laid-Open No. 167703-1997. In the gazette, a study is made with a particular emphasis on a Z-type hexagonal ferrite (Ba, Sr, Pb)
3
(Co
1−X
Cu
X
)
2
Fe
24
O
42
, and V
2
O
5
, CuO, Bi
2
O
3
, MoO
3
, WO
3
and PbO are added to attempt firing at low temperatures.
Further, in the gazette, reports are made on firing of a hexagonal ferrite whose primary phase is an M-type, Y-type, W-type, X-type or U-type. Particularly, in the case of a hexagonal ferrite with a Y-type primary phase which is disclosed in a specific example, that is, (Ba)
2
(Co
1−X
Cu
X
)
2
Fel
12
O
22
, the proportion of Y-type hexagonal ferrite is not described and unknown, but since its calcination temperature is as extremely low as 700° C., its proportion is as high as about 50%, or lower when additives are added, so that it can be said that the proportion does not exceed 80% unlike the present invention. Therefore, obtained magnetic properties are not satisfactory at all. That is, although the compositions and the addition of the substances in the gazette make low-temperature firing possible, the calcination temperature is not studied sufficiently, and the magnetic properties after firing cannot be fully exhibited due to a low yield of soft magnetic phase after sintering. It can be said that this causes the problem that a high inductance and a high impedance cannot be obtained easily.
In addition, the content of CuO in the gazette is lower than that in the present invention, and there exists the problem that even if the effect of additives is considered, high properties cannot be obtained by increasing the yield of the Y-type hexagonal ferrite by firing about 900° C.
(2) In addition to the problems described in the above (1), there still exist the following problems to be solved. That is, the electric resistivity of a conventional, so-called Y-type hexagonal ferrite is as high as about 1×10
5
&OHgr;·m at the highest, while the electric resistivity of a Y-type hexagonal ferrite substituted with Cu or Zn for the purpose of obtaining high properties is about 1×10
4
&OHgr;·m, and it cannot but be said that these values are lower than the values exceeding an electric resistivity of 1×10
5
&OHgr;·m which is required for materials for electronic parts.
Further, since a hexagonal ferrite has a higher dielectric constant than a spinel-type ferrite, parasitic capacitance occurring in an inductor becomes large, so that the inductor is liable to cause self-resonance and an inductance and an impedance are lowered.
(3) Even if the problems described in the above (1) are solved to some degree, a further improvement in magnetic properties or the like, particularly a further improvement in permeability within a high-frequency band, is desired in the technical field associated with the present application.
By further improving the permeability within a high-frequency band, a higher inductance can be obtained (i) when the hexagonal ferrite is used as an inductance part, and higher impedance properties can be obtained (ii) when the hexagonal ferrite is used as a noise filter part.
(4) In addition to the problem described in the above (3), there still exist the following problems to be solved. That is, the electric resistivity of a conventional, so-called Y-type hexagonal ferrite is as high as about 1×10
5
&OHgr;·m at the highest while the electric resistivity of a Y-type hexagonal ferrite substituted with Cu or Zn for the purpose of obtaining high properties is about 1×10
4
&OHgr;·m, and it cannot but be said that these values are lower than the values exceeding an electric resistivity of 1×10
5
&OHgr;·m which is required for materials for electronic parts.
Further, since a hexagonal ferrite has a higher dielectric constant than a spinel-type ferrite, parasitic capacitance occurring in an inductor becomes large, so that the inductor is liable to cause self-resonance and an inductance and an impedance are lowered.
DISCLOSURE OF THE INVENTION
The present invention has been invented to solve the above problems of the prior art. That is, the invention of a first group of the present invention has been invented for solving the problem of the prior art which has been described in the above (1). An object thereof is to provide a sintered body which exhibits good magnetic properties and is usable up to a high frequency band ranging from several hundred megahertz to gigahertz, contains as few hetero phases other than a Y-type hexagonal ferrite as possible and can be calcined at a temperature of not higher than 1,000° C., particularly about 900° C., and a high-frequency circuit component using the sintered body. To solve such a problem, the present invention is a sintered body at least 80% of which is constituted of a Y-type hexagonal ferrite, wherein the sintered body contains, as main components, a cobalt oxide in an amount of 3 to 15 mol % in terms of CoO, a copper oxide in an amount of 5.5 to 17 mol % in terms of CuO, an iron oxide in an amount of 57 to 61 mol % in terms of Fe
2
O
3
and AO (AO is at least one of BaO or SrO) as the balance, and also contains, as an additional component, 0.5 to 7 wt % of bismuth oxide (Bi
2
O
3
). Further, the present invention is a high-frequency circuit component having the structure that a conductive body is embedded in a sintered body, wherein a Y-type hexagonal ferrite constitutes at least 80% of the sintered body, and the sintered magnetic oxide contains, as main components, a cobalt ox
Murase Taku
Umeda Hidenobu
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