Compositions – Magnetic – Iron-oxygen compound containing
Reexamination Certificate
2003-05-30
2004-08-10
Lam, Cathy (Department: 1775)
Compositions
Magnetic
Iron-oxygen compound containing
C252S062580, C428S689000, C428S690000
Reexamination Certificate
active
06773620
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an oxide magnetic material usable for a multilayer inductor and a laminated ceramic substrate and the like in a high frequency circuit member and the like and its production method.
2. Related Art
With the recent trend of miniaturization and use of higher frequency of electronic apparatus, a magnetic material usable in a high frequency band is more and more needed. As such a magnetic material for high frequency, NiCuZn-series spinel ferrites have been conventionally used, however in the case of frequency of several hundred MHz or higher, they cause natural resonance to result in increase of the loss and become incapable of practically working as magnetic materials. As a magnetic material usable up to a GHz band, hexagonal ferrites with high magnetic anisotropy defined as Ba
3
Me
2
Fe
24
O
42
(Me: a bivalent metal) and the like can be exemplified. Further, in order to improve the high frequency properties by improving the anisotropy, it is tried to replace some of Ba in the above-mentioned hexagonal type ferrites with Sr.
However, in the GHz band, the imaginary component (&mgr;″) of the magnetic permeability becomes so significant as to increase the loss for use such ferrites for inductors.
Also, in a high frequency circuit member, use of a laminated ceramic substrate comprising a magnetic ceramic substrate and a dielectric ceramic substrate laminated on each other has been tried for miniaturization. With respect to such a laminated ceramic substrate, the patterned wiring of a capacitor is formed on a dielectric ceramic substrate and the patterned wiring of an inductor is formed on a magnetic ceramic substrate.
FIG. 4
is a perspective view showing one example of such a laminated ceramic substrate and
FIG. 5
is an exploded perspective view. As illustrated in FIG.
4
and
FIG. 5
, the laminated ceramic substrate is composed by laminating a plurality of ceramic substrates
3
and
4
. A plurality of wiring patterns
11
composing inductors and capacitors are formed on the surfaces of the respective ceramic substrates
3
and
4
by a screen-printing method or the like.
In the case the ceramic substrates
3
are magnetic ceramic substrates and the ceramic substrates
4
are dielectric ceramic substrates, the wiring patterns
11
composing the inductors are formed on the magnetic ceramic substrates
3
and wiring patterns
11
composing the capacitors are formed on the dielectric ceramic substrates
4
. The wiring patterns
11
between the substrates are connected through via holes
12
.
After laminated, these ceramic substrates
3
and
4
are united by firing at a high temperature to obtain a laminated ceramic substrate.
In the case the wiring patterns
11
are formed by using Ag or the like with a high conductivity, it is required to carry out firing at a temperature as low as about 900° C. If firing is carried out at a high temperature, the shape of the wiring patterns of Ag or the like is deformed to make it impossible to form desired circuits on the respective substrates.
However, a conventional magnetic ceramic material like a hexagonal ferrite or the like has a suitable firing temperature of 1,300° C. or higher, and it has a problem that good magnetic properties cannot be obtained in the case firing is carried out at a temperature as low as about 900° C.
It has been tried to carry out firing at a low temperature by adding a sintering aid such as B
2
O
3
, CuO, and Bi
2
O
3
, neither sufficient effect on low temperature firing has been obtained yet nor the magnetic loss has been lowered sufficiently. Especially, with respect to a hexagonal ferrite in which some of Ba's are replaced with Sr's, any sufficient effect has not been obtained so far.
SUMMARY OF THE INVENTION
The object of the present invention is to provide an oxide magnetic material which can be produced by firing at a low temperature and has good magnetic properties in a high frequency band and its production method.
The oxide magnetic material of the invention is a Sr-containing oxide magnetic material having grain boundary phases in crystal grains, containing not less than 2% by weight of Sr in the grain boundaries and not less than 10% by weight of at least one element selected from Bi, V, B and Cu.
With respect to the oxide magnetic material of the invention, existence of not less than 2% by weight of Sr in the grain boundaries and not less than 10% by weight of the above-mentioned elements in the material can decrease the magnetic loss and give good magnetic properties. Further, the oxide magnetic material can be produced by firing at a low temperature.
The content of Sr in the grain boundary phases is preferably not less than 2% by weight, more preferably not less than 5% by weight and its upper limit is preferably not more than 30% by weight. When the content of Sr in the grain boundary phases is less than 2% by weight, shrinkage after firing at a temperature as low as about 900° C. is scarcely observed and a specimen after firing is unsatisfactory in the mechanical strength or the like and the magnetic loss is increased. On the other hand, if the Sr content exceeds 30% by weight, the content of other elements such as Bi and the like is relatively decreased, so that densification in the case of low temperature firing sometimes does not take place.
The content of the additive elements in the grain boundary phases is preferably not less than 10% by weight, more preferably not less than 25% by weight and its upper limit is not more than 70% by weight. If the content of additive elements is less than 10% by weight, shrinkage after firing at a temperature as low as about 900° C. is scarcely observed and a specimen after firing is unsatisfactory in the mechanical strength or the like and the magnetic loss is increased. On the other hand, if the content of additive elements exceeds 70% by weight, the magnetic permeability (a real component) decreases in some cases.
As for the additive elements, use of Bi is especially preferred. The additive elements may be contained in an oxide magnetic material by adding oxides containing the additive elements to a preliminarily baked powder obtained by preliminarily baking a raw material powder of the oxide magnetic material and firing the obtained mixture. The oxides containing the additive elements include Bi
2
O
3
, V
2
O
5
, B
2
O
3
, CuO, and the like. The content of the additive elements in the grain boundary phases can be adjusted by adjusting the amount of the oxides to be added to a preliminarily baked powder.
In the invention, together with the oxides containing additive elements, an oxide containing Sr may be added to the preliminarily baked powder and the obtained mixture may be fired to add Sr in the oxide magnetic material. Addition of the oxide containing Sr to the preliminarily baked powder increases the content of Sr especially in grain boundary phases. The content of Sr in the grain boundary phases can be also controlled by changing the pulverizing and mixing conditions at the time of pulverizing and mixing the preliminarily baked powder and the oxide containing Sr. For example, if the mixing is carried out for a long duration, the content of Sr in the grain boundary phases can be increased. Further, the content of Sr in the grain boundary phases can be controlled by changing the temperature at the time of preliminarily baking the raw material powder of the oxide magnetic material. That is, if the preliminarily baking temperature is decreased, the content of Sr in the grain boundary phases can be increased.
In the invention, Si may be contained further in the grain boundary phases. The content of Si in the grain boundary phases is preferably not less than 2% by weight, more preferably not less than 3% by weight and its upper limit is preferably not more than 20% by weight. Existence of Si in the grain boundary phases increases the shrinkage ratio of a fired oxide magnetic material and improves the magnetic properties. If the content of Si in the grain boundary
Hirano Hitoshi
Umemoto Takashi
Yoshikawa Hideki
Arent & Fox PLLC
Lam Cathy
Sanyo Electric Co,. Ltd.
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