Compositions – Magnetic – Iron-oxygen compound containing
Reexamination Certificate
2002-08-27
2004-11-09
Koslow, C. Melissa (Department: 1755)
Compositions
Magnetic
Iron-oxygen compound containing
C252S062640, C252S062600, C252S062620
Reexamination Certificate
active
06814883
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high frequency magnetic material and a high frequency circuit element including the same.
2. Description of the Related Art
Among circuit components for mobile communication devices such as mobile phones and wireless LAN, an inductance element and an impedance element are known. The inductance element is used as a component for impedance-matching circuits, resonant circuits and choke coils. The impedance element is used as a component for devices for suppressing noise, which is called electromagnetic interference and is hereinafter referred to as EMI. Since devices using high frequency have been increasing, it is also necessary for circuit components used for these devices to operate at a frequency of several hundred MHz to several GHz.
A hexagonal ferrite has been proposed as a material for devices that can operate at a frequency of several hundred MHz to several GHz. This material maintains permeability in a frequency band exceeding the frequency at which a spinel ferrite cannot maintain permeability. The hexagonal ferrite referred to herein is a magnetic material called a ferrox planar type ferrite, which has an easy magnetization axis in a plane perpendicular to the c-axis and was reported in the beginning of 1957 by Phillips Corporation.
A typical magnetic material of the ferrox planar type ferrite includes a Co-substituted Z type hexagonal ferrite expressed by the composition formula 3BaO.2CoO.12Fe
2
O
3
(Co
2
Z), a Co-substituted Y type hexagonal ferrite expressed by the composition formula 2BaO.2CoO.6Fe
2
O
3
(Co
2
Y), and a Co-substituted W type hexagonal ferrite expressed by the composition formula BaO.2CoO.8Fe
2
O
3
(Co
2
W).
Among the above ferrox planar type ferrites, the Y type hexagonal ferrite has a large anisotropic magnetic field perpendicular to the c-axis and has a large threshold frequency in the relationship between the frequency and the permeability. The Co-substituted W type hexagonal ferrite expressed by the composition formula BaO.2CoO.8Fe
2
O
3
(Co
2
W), which is typical of a Y type hexagonal ferrite, has a certain permeability at a frequency of up to several GHz and is therefore expected to be usable as a magnetic material for devices operating at a frequency of several hundred MHz to several GHz.
However, the firing temperature must be 1,150° C., which is very high, in order that the ferrox planar type ferrite has a relative X-ray density of 90% or more. The relative X-ray density is herein defined as a ratio of the measured density of a sintered compact to the theoretical density, determined using X-rays.
Inductance elements and impedance elements are manufactured by firing green compacts including magnetic layers comprising a magnetic material and conductor layers comprising Ag or Ag—Pd, which has a small relative resistance. Therefore, the diffusion of Ag and the destruction of the inner conductor must not arise in sintered compacts during the firing. It is thus necessary to use a magnetic material providing sintered compacts having a relative X-ray density of about 90% or more when the green compacts are fired at 1,100° C. or less, and preferably at 1,000° C. or less. When the sintered compacts have a relative X-ray density of about 90% or more, practical inductance elements or impedance elements can be manufactured in terms of the mechanical strength of elements.
A ferrox planar type hexagonal ferrite is disclosed in Japanese Unexamined Patent Application Publication No. 9-167703. However, it is not indicated in the publication that the hexagonal ferrite expressed by the composition formula (1-a-b)(Ba
1-x
Sr
x
)O.aMeO.bFe
2
O
3
or (1-a-b)(Ba
1-x
Sr
x
)O.a(Me
1-y
Cu
y
)O.bFe
2
O
3
, in which the ratio b/a is 2.2 or more to less than 3, can be sintered at low temperature. In the publication, substituting Ba with Pb is described but substituting Ba with Sr is not described. Effects obtained by firing the hexagonal ferrite in which Ba is substituted with Sr at low temperature are not also described.
Furthermore, a ferrox planar type hexagonal ferrite is also disclosed in Japanese Unexamined Patent Application Publication No. 9-246031. However, what is described in the publication is only how to sinter a Z type hexagonal ferrite at low temperature.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a high frequency magnetic material used for manufacturing an impedance element including an Ag or Ag—Pd inner conductor and having the excellent characteristic of suppressing EMI at a frequency of several hundred MHz to several GHz.
It is another object of the present invention to provide a high frequency magnetic material including a Y or M type hexagonal ferrite which absorbs noise and has high sintered density and permeability in which the imaginary part &mgr;″ is small at a frequency of less than 1 GHz and is large at a frequency of 1 GHz or more.
It is another object of the present invention to provide a high frequency magnetic material including a Y type hexagonal ferrite for impedance elements having high sintered density and the high Q
m
value (the ratio of the real part of the permeability to the imaginary part of the permeability) at a frequency of several GHz.
Furthermore, it is another object of the present invention to provide an inductance element and an impedance element operating at a frequency of several hundred MHz to several GHz using such a high frequency magnetic material.
In a first aspect of the present invention, a high frequency magnetic material includes a Y or M type hexagonal ferrite, wherein the hexagonal ferrite is expressed by the composition formula (1-a-b)(Ba
1-x
Sr
x
)O.aMeO.bFe
2
O
3
, where Me is at least one selected from the group consisting of Co, Ni, Cu, Mg, Mn and Zn, 0.205≦a≦0.25, 0.55≦b≦0.595, 0≦x≦1 and 2.2≦b/a<3.
In a second aspect of the present invention, a high frequency magnetic material includes a Y or M type hexagonal ferrite, wherein the hexagonal ferrite is expressed by the composition formula (1-a-b)(Ba
1-x
Sr
x
)O.a(Co
1-y
Cu
y
)O.bFe
2
O
3
, where 0.205≦a≦0.25, 0.55≦b≦0.595, 0≦x≦1, 0.25≦y≦0.75 and 2.2≦b/a<3.
In a third aspect of the present invention, a high frequency magnetic material includes a Y or M type hexagonal ferrite, wherein the hexagonal ferrite is expressed by the composition formula (1-a-b)(Ba
1-x
Sr
x
)O.a(Co
1-y-z
Cu
y
Me
z
)O.bFe
2
O
3
, where Me is at least one selected from the group consisting of Ni, Mg and Zn, 0.205≦a≦0.25, 0.55≦b≦0.595, 0≦x≦1, 0.25≦y≦0.75, 0<z≦0.75, 0.25≦y+z≦0.75 and 2.2≦b/a<3.
In a fourth aspect of the present invention, a high frequency magnetic material includes a Y or M type hexagonal ferrite, wherein the hexagonal ferrite is expressed by the composition formula (1-a-b)(Ba
1-x
Sr
x
)O.a(Co
1-y-z
Cu
y
Zn
z
)O.bFe
2
O
3
, where 0.205≦a≦0.25, 0.55≦b≦0.595, 0≦x≦1,0.25≦y≦0.75, 0<z≦0.75,0.25≦y+z≦0.75 and 2.2≦b/a<3.
The high frequency magnetic materials of the first to fourth aspects may further include about 0.1 to 30% by weight of Bi
2
O
3
.
In a fifth aspect of the present invention, a high frequency circuit element includes magnetic layers and internal electrode layers, wherein the high frequency circuit element is a sintered compact and the magnetic layers comprise the high frequency magnetic material according to any one of the first to fourth aspects.
A high frequency magnetic material of the present invention includes the hexagonal ferrite expressed by the composition formula (1-a-b)(Ba
1-x
Sr
x
)O.aMeO.bFe
2
O
3
, in which the ratio b/a is 2.2 or more to less than 3. When a green compact includes the high frequency magnetic material, a sintered compact having a relative X-ray density of 90% or more can be obtained by firing the green compact at low temperature, for example, 1,100° C. or less. The sintered compact includes a Y or M type hexagonal ferrite as a main phase. In the
Koslow C. Melissa
Murata Manufacturing Co. Ltd.
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