Compositions – Magnetic – Iron-oxygen compound containing
Reexamination Certificate
2002-02-14
2004-06-15
Koslow, C. Melissa (Department: 1755)
Compositions
Magnetic
Iron-oxygen compound containing
C252S062600, C252S062640, C428S611000, C036S03600C, C036S181000, C036S083000
Reexamination Certificate
active
06749768
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to magnetic ferrite used in a multilayer ferrite chip component such as a multilayer ferrite chip bead and a multilayer inductor and used in an integrated multilayer component represented by an Lc integrated multilayer component, and to a multilayer ferrite chip component.
2. Background Art
A multilayer ferrite chip component and an integrated multilayer component (collectively referred to as a “multilayer ferrite chip component” in the specification) are used in various electric appliances because of a small volume and high reliability. The multilayer ferrite chip component is normally manufactured by the following process. A sheet or paste for a magnetic layer made of magnetic ferrite and paste for an internal electrode are made into a monolithic laminated strucure using a thick film stacking technology, and then sintered. Then, paste for an external electrode is printed or transferred on a surface of the sintered body obtained, and then baked. Note that sintering after obtaining the monolithic laminated strucure is referred to as co-firing. Ag or an Ag alloy is used as a material for the internal electrode because of their low resistivity. Accordingly, as for the magnetic ferrite material constituting the magnetic layer, it is an absolute condition that the material is capable of co-firing, in other words, capable of being sintered at a temperature lower than the melting point of Ag or an Ag alloy. Therefore, whether or not the magnetic ferrite can be sintered at a temperature lower than the melting point of Ag or an Ag alloy is a key to obtaining a multilayer ferrite chip component of high density and high-level characteristics.
NiCuZn ferrite is known as the magnetic ferrite that can be sintered at a temperature lower than the melting point of Ag or an Ag alloy. at a temperature lower than the melting point of Ag or an Ag alloy. Specifically, the NiCuZn ferrite using raw material powder with a specific surface area of about 6 m
2
/g or greater produced by fine milling can be sintered at a temperature lower than the melting point of Ag (961.93° C.). Accordingly, the NiCuZn ferrite is widely used in the multilayer ferrite chip components.
In recent years, hexagonal ferrite has drawn attention with an increase of a clock frequency. There are six kinds of the hexagonal ferrite, namely, an M type, a U type, a W type, an X type, a Y type and a Z type, which have characteristics different from cubic ferrite of an Mn based ferrite and an Ni based ferrite. Among these kinds, the Z type has a general formula of M
3
Me
2
Fe
24
O
41
. Here, M denotes alkaline-earth metal, and Me denotes bivalent metal ions. Among the Z types of the hexagonal ferrite, a Z type hexagonal ferrite containing cobalt metal ions has large anisotropy. Thus, the Z type hexagonal ferrite containing cobalt metallic ions is capable of having high permeability up to a frequency range higher than that of spinel ferrite. The Z type hexagonal ferrite containing cobalt metallic ions is referred to as Co
2
Z.
Although the fact that the Z type hexagonal ferrite has an excellent high frequency characteristic has been known from before, it has not been put into practical use yet due to several problems. Specifically, phases of M, W and Y appear in the course of generation of Z phase, and generation of the different phases reduces the permeability. Moreover, it is also pointed out that sintered hexagonal ferrite of the Z type has low sintered body density. If the sintered body density is low, low mechanical strength of the sintered body when used as a surface mount component becomes a problem. In addition, the sintered body density and the permeability are closely related to each other, as the permeability itself is reduced if the sintered body density is low. Thus, original magnetic properties cannot be exerted.
Japanese Patent Laid-Open No. Hei9 (1997)-110432 gazette discloses a hexagonal ferrite material in which sintered body density thereof is increased and the permeability reduction in high frequency region is suppressed. The hexagonal ferrite material disclosed in Japanese Patent Laid-Open No. Hei9 (1997)-110432 gazette is characterized in that SiO
2
and CaO are added by predetermined amounts. However, the hexagonal ferrite material disclosed in Japanese Patent Laid-Open No. Hei9 (1997)-110432 gazette is based on the assumption that the material is sintered at a temperature in a range from 1150° C. to 1350° C. Accordingly, the co-firing cannot be performed, and application to the multilayer ferrite chip components is difficult.
Japanese Patent Laid-Open No. Hei9 (1997)-167703 gazette discloses an approach to a low-temperature sintering of a hexagonal ferrite material. Specifically, the gazette points out that a composition of (Ba, Sr, Pb)
3
(Co
1-x
Cu
x
)
2
Fe
24
O
41
, that is, substitution of a portion of the alkaline-earth metal with Pb and also substitution of a portion of Co with Cu, allows the hexagonal ferrite material to be dense at a low temperature. However, the hexagonal ferrite material obtained by Japanese Patent Laid-Open No. Hei9 (1997)-167703 gazette has the phases of M, Y, W, X and U as main phases, and has not obtained the hexagonal ferrite material having the Z phase as a main phase, which is highly permeable to the high frequency range.
As described above, a hexagonal ferrite material capable of sintering at a low temperature and having the Z phase as a main phase has not been obtained yet.
SUMMARY OF THE INVENTION
Disclosure of the Invention
An object of the present invention is to provide a hexagonal ferrite material that can be applied to a multilayer ferrite chip component because of capability of low-temperature sintering and that has Z phase as a main phase, and a multilayer ferrite chip component using such material.
Conventionally, hexagonal ferrite of the Z type usable in a GHz-range has not been able to sinter at a temperature lower than the melting point of Ag, which constitutes a material for an internal electrode. This is because magnetic properties cannot be obtained unless the ferrite is sintered at a high temperature in a range from 1250° C. to 1350° C. Therefore, it has not been possible to obtain a multilayer ferrite chip component which requires co-firing with Ag by using the hexagonal ferrite of the Z type. Although a hexagonal ferrite material that can be sintered at a low temperature has been proposed, such material does not have Z phase as a main phase. The inventors therefore examined a calcining temperature, a grain size distribution of powder before sintering, a powder specific surface area, and an additive to a main composition, and solved the foregoing problems.
The present invention provides magnetic ferrite powder in which a peak intensity ratio of the Z phase of the hexagonal ferrite (M
3
Me
2
Fe
24
O
41
: M=one or more kinds of alkaline-earth metal, Me=one or more kinds selected from Co, Ni, Mn, Zn, Mg and Cu) is 30% or higher in X-ray diffraction and a peak value of grain size distribution is within a range from 0.1 &mgr;m to 3 &mgr;m.
The magnetic ferrite powder of the present invention can be added with one or more kinds selected from borosilicate glass, zinc borosilicate glass, Bi
2
O
3
based glass, CuO and Bi
2
O
3
, by 0.5 wt % to 20 wt %. Among the above, it is preferable to add CuO and Bi
2
O
3
by 0.5 wt % to 20 wt % in total, or to add Bi
2
O
3
based glass and CuO by 1 wt % to 20 wt % in total. In particular, it is preferable to add Bi
2
O
3
based glass by 3 wt % to 7 wt % and CuO by 3 wt % to 7 wt %.
The present invention also provides magnetic ferrite powder in which Z phase (M=Ba, Me=one or more kinds selected from Co, Ni, Mn, Zn, Mg and Cu) indicated as M
3
Me
2
Fe
24
O
41
forms a main phase and a powder specific surface area is 5 m
2
/g to 30 m
2
/g. In the magnetic ferrite powder of the present invention, the magnetic ferrite having an excellent high frequency characteristic can be obtained by substituting a portion of Ba with Sr, and calc
Endo Masami
Nakano Atsuyuki
Koslow C. Melissa
Pearne & Gordon LLP
TDK Corporation
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