Dielectric ceramic composition

Details Dielectric ceramic composition Dielectric ceramic composition

2001-07-20

2002-10-01

Brunsman, David (Department: 1755)

Compositions: ceramic

Ceramic compositions

Titanate, zirconate, stannate, niobate, or tantalate or...

C501S138000, C361S321400, C361S321500, C428S427000, C428S432000

Reexamination Certificate

active

06458734

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to dielectric ceramic compositions which are suitably used in a high frequency band, such as a microwave or a milliwave band, and which are used for forming microwave resonators, filters and laminated capacitors, and relates to a dielectric ceramic compact and multilayer ceramic substrates, ceramic electronic devices, and laminated ceramic electronic devices formed of the dielectric ceramic compacts.
2. Description of the Related Art
In order to miniaturize electronic devices, such as a microwave resonator and a filter, a structure formed of a dielectric ceramic material having a high relative dielectric constant has been proposed in place of a cavity resonator. When the relative dielectric constant of a dielectric material is represented by e, by exploiting the effect where the wavelength of an electromagnetic wave in the dielectric material is shortened by a factor of (1/∈)
½
of the wavelength in free space, miniaturization of a microwave resonator and a filter has been attempted by using a dielectric ceramic material having a high relative dielectric constant.
However, the relative dielectric constant ∈ of a dielectric ceramic having a temperature coefficient which can be practically used for a dielectric resonator has been up to 100 or less, and as a result, it has been difficult to meet the requirement of further miniaturization.
Accordingly, a method using an LC resonator which is a known microwave circuit has been proposed to perform further miniaturization under the limitations of the relative dielectric constant of the dielectric ceramic. That is, by applying a laminating method which is practically used for forming laminated capacitors and multilayer substrates to the formation of an LC circuit, microwave electronic devices can be even further miniaturized and the reliability thereof can be improved.
However, in order to obtain an LC resonator having a high Q in a microwave band, the electrical conductivity of internal electrodes embedded in a laminated capacitor or in a multilayer circuit substrate must be high. As an internal electrode which can be simultaneously fired together with a dielectric material or a multilayer circuit substrate, a metal having a high electrical conductivity, such as gold (Au), silver (Ag) or copper (Cu), must be used.
Accordingly, the dielectric ceramic compact must have a high relative dielectric constant, a high Q, and a small temperature coefficient thereof, and in addition to these, the dielectric ceramic compact must be a material which can be obtained by co-sintering together with an internal electrode composed of a metal having a low melting point. A material which can meet all of these requirements has not been obtained up to now.
For example, since a metal such as Ag, Au or Cu has a melting point of approximately 960 to 1,063° C., and a conventional dielectric ceramic composition has a high firing temperature of 1,350° C. or more, co-sintering cannot be performed with the metal having superior electrical conductivity.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a dielectric ceramic composition which has a high relative dielectric constant, a high Q, and a small temperature coefficient after sintering and, in addition, which can be sintered at a relatively low temperature.
Another object of the present invention is to provide a dielectric ceramic compact obtained by sintering the dielectric ceramic composition, a multilayer ceramic substrate, a ceramic electronic device and a laminated ceramic electronic device, which are formed of the dielectric ceramic compact described above and which has superior high frequency properties.
To these ends, in accordance with one aspect of the present invention, a dielectric ceramic composition comprises a BaO—TiO
2
—ReO
3/2
-based ceramic composition represented by the formula xBaO—yTiO
2
—zReO
3/2
and a glass composition; wherein, in the formula xBaO-yTiO
2
—zReO
3/2
, 8≦x≦18, 52.5≦y≦65 and 20≦z≦40, x, y, and z being mole percent, x+y+z=100, and Re indicates a rare earth element, and the glass composition comprises about 10 to 25 wt % of SiO
2
, about 10 to 40 wt % of B
2
O
3
, about 25 to 55 wt % of MgO, 0 to about 20 wt % of ZnO, 0 to about 15 wt % of Al
2
O
3
, about 0.5 to 10 wt % of Li
2
O and 0 to about 10 wt % of RO in which R is at least one selected from the group consisting of Ba, Sr and Ca.
In the dielectric ceramic composition described above, the glass component is preferably Pb-free glass. In addition, the BaO—TiO
2
—ReO
3/2
-based dielectric ceramic is preferably Bi-free dielectric ceramic.
In addition to the primary component composed of the BaO—TiO
2
—ReO
3/2
-based dielectric ceramic and the glass component, the dielectric ceramic compact described above may further comprise CuO as a subcomponent.
In addition to the primary components composed of the BaO—TiO
2
—ReO
3/2
-based dielectric ceramic and the glass component, the dielectric ceramic composition described above may further comprise TiO
2
as a subcomponent.
In the dielectric ceramic composition described above, the content of the glass composition is preferably in the range of from about 15 to 35 wt % with respect to about 65 to 85 wt % of the BaO—TiO
2
—ReO
3
-based ceramic composition.
In accordance with another aspect of the present invention, a dielectric ceramic composition comprises a BaO—TiO
2
—ReO
3/2
-based ceramic composition represented by the formula xBaO—yTiO
2
—ReO
3/2
, a glass composition, CuO, and TiO
2
; wherein 8≦x≦18, 52.5≦y≦65, and 20≦z≦40, x, y, and z being mole percent and x+y+z=100, and Re indicates a rare earth element, and the glass composition comprises about 10 to 25 wt % of SiO
2
, about 10 to 40 wt % of B
2
O
3
, about 25 to 55 wt % of MgO, 0 to about 20 wt % of ZnO, 0 to about 15 wt % of Al
2
O
3
, about 0.5 to 10 wt % of Li
2
O, and 0 to about 10 wt % of RO in which R is at least one selected from the group consisting of Ba, Sr and Ca, and the contents of the BaO—TiO
2
—ReO
3/2
-based ceramic composition, the glass composition, the TiO
2
and the CuO are about 65 to 85 wt %, about 15 to 35 wt %, about 0.1 to 10 wt %, and about 3 wt % or less, respectively.
In the dielectric ceramic composition described above, the glass component is preferably Pb-free glass. In addition, the BaO—TiO
2
—ReO
3/2
-based dielectric ceramic is preferably Bi-free dielectric ceramic.
Since the BaO—TiO
2
—ReO
3/2
-based ceramic composition represented by the specific formula xBaO—yTiO
2
—zReO
3/2
and the specific glass composition described above are used as primary materials, as will be apparent in examples described later, sintering at a low temperature of not more than 1100° C., preferably 1000° C. or less, can be performed, and hence, co-sintering with a metal having superior conductivity, such as Ag, Au or Cu, can also be performed.
In addition, a dielectric ceramic compact, which obtained by sintering the dielectric ceramic composition, can be obtained having a small temperature coefficient and a high relative dielectric constant in a high frequency band, more specifically, in a microwave band and a milliwave band.
Furthermore, when the glass component composed of the glass composition is crystallized, or the BaO—TiO
2
—ReO
3/2
-based ceramic composition and the glass composition form a crystal phase by reaction with each other, a crystal phase having a high Q, such as Mg
2
B
2
O
5
, Mg
3
B
2
O
6
, BaTi
4
O
9
, Ba
2
Ti
9
O
20
, Mg
2
TiO
4
,Mg
2
SiO
4
, Zn
2
TiO
4
, Zn
2
Ti
3
O
8
or ZnAl
2
O
4
is precipitated, whereby a dielectric ceramic compact having a high Q can be obtained.
The rare earth element Re used for the BaO—TiO
2
—ReO
3/2
-based ceramic composition is not specifically limited, and for example, Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu may be optionally used alone or in combination.
The reasons the composition represented by xBaO—yTiO
2
—zReO
3/2
are

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