Dielectric ceramic composition

Details Dielectric ceramic composition Dielectric ceramic composition

2002-04-17

2004-05-25

Group, Karl (Department: 1755)

Compositions: ceramic

Ceramic compositions

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

C501S136000

Reexamination Certificate

active

06740613

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dielectric ceramic composition which is widely used in high frequency electronic components and, more particularly, to a low-temperature cofired dielectric ceramic composition with a high dielectric constant and a low dielectric loss.
Low-temperature cofired dielectric compositions (materials) means compositions(materials) which can be fired in the temperature range of 800-950° C., lower than the melting point of silver (Ag) or copper (Cu), in contrast to the conventional ceramic dielectrics which are sintered at 1,300° C. or higher.
2. Description of the Prior Art
The strong recent tendency toward miniaturization, lightness and intelligence of electric and electronic appliances has demanded a considerable reduction in the size and number of substituent devices on circuit boards as well as the high performance thereof. To meet the demands, there have been made extensive attempts in some of which part-on-boards are multi-layered, followed by firing dielectrics and electrodes simultaneously.
However, high sintering temperatures of conventional dielectric materials require the use of high melting temperature metals, such as Mo or W, in inner electrode patterns in order to achieve the multilayering and simultaneous firing of circuit boards and device parts.
Where Mo or W is adopted in inner electrode patterns, however, an economic disadvantage is incurred because of its high cost. Above all, the skin effect, which causes radio frequency current to stay near the surface of a conductor, requires that metals of low electric resistance be used for the electrode patterns in order to reduce the dielectric loss. Accordingly, there have been indispensably used metals that are relatively inexpensive as well as being of high electric conductivity, like Ag or Cu.
As Ag or Cu is used in inner electrode patterns, a very important research subject is to find a dielectric material which can be fired at lower than the melting point of Ag (960° C.) or Cu (1083° C.).
Typically, low-temperature fired dielectrics are prepared by liquid-phase sintering an admixture comprising high-temperature fired material with a high dielectric constant and low dielectric loss in combination with a small amount of a low melting point material, for example, glass powder or an additive such as CuO, PbO and Bi
2
O
3
, V
2
O
5
, etc., or by firing glass ceramics comprising ceramics as a filler.
When the latter is used, the resulting dielectric substrates based on glass show a dielectric constant of 10 or less.
With advantages of low dielectric constants in speeding-up signal processing and improving signal transmission, materials with a low dielectric constant of 10 or less are extensively used for low temperature cofired ceramics (LTCC).
Meanwhile, depending on characteristics of applied circuits, substrates made of dielectrics with low dielectric loss and medium dielectric constant (15-100) may often enjoy advantages in terms of circuit design and function without retardation of signal processing.
As a rule, however, use of dielectrics with high dielectric constants makes the guided wavelength short, leading to a reduction in circuit dimension. Thus, such dielectrics are very useful in applications which attach importance to dimensions of electric elements, as well as having the advantage of reducing insertion loss properties or frequency deviation according to circuits.
Larger dielectric constants can lower the ratio of the width of transmission lines to the thickness of dielectrics to greater extents, giving circuit designers an opportunity to design better lamination structures.
ZrO
2
—AO—B
2
O
5
—TiO
2
(A=Zn, Mg, Co, Mn, and B=Nb, Ta)-based dielectric compositions with dielectric constants of approximately 40 or higher are disclosed in U.S. Pat. No. 5,470,808. These dielectric compositions can be fired at temperatures of 1,300° C. or higher, which are too high to co-fire Ag electrodes. That is, ZrO
2
—AO—B
2
O
5
—TiO
2
(A=Zn, Mg, Co, Mn, and B=Nb, Ta)-based dielectric compositions alone have difficulty in being used for TLCC.
SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to overcome the above problems encountered in prior arts and provide a dielectric ceramic composition which exhibits high dielectric constant and low dielectric loss and can be sintered at low temperature.
It is another object of the present invention to provide a dielectric ceramic composition which is improved in sintering properties as well as being controllable in high frequency dielectric properties.
In accordance with an aspect of the present invention, there is provided a dielectric ceramic composition represented by the following chemical formula 1:
 
a
wt. % {
x
ZrO
2
−y
ZnO−
w
Nb
2
O
5
−z
TiO
2
}+c
wt. % Glass Frit  Chemical Formula 1
wherein, 5.0 mol %≦x≦45.0 mol %; 1.5 mol % ≦y≦19.0 mol %; 1.5 mol %≦w≦19.0 mol %; 40.0 mol %≦z≦59.0 mol % with the proviso that x+y+w+z=100; 75.0≦a≦97.0; and 3.0≦c≦25.0.
In accordance with another aspect of the present invention, there is provided a dielectric ceramic composition represented by the following chemical formula 2:
a
wt. % {
x
ZrO
2
−y
ZnO−
w
Nb
2
O
5
−z
TiO
2
}+b
wt. % (MgO, CoO, SiO
2
, Sb
2
O
3
, Sb
2
O
5
, MnO
2
, Ta
2
O
5
or combinations thereof)+
c
wt. % ZnO—B
2
O
3
—SiO
2
based Glass Frit  Chemical Formula 2
wherein, 5.0 mol % ≦x≦45.0 mol %; 1.5 mol %≦y≦19.0 mol %; 1.5 mol %≦w≦19.0 mol %; 40.0 mol %≦z≦59.0 mol % with the proviso that x+y+w+z=100; 75.0≦a≦97.0; b≦1.5; and 3.0≦c≦25.0).
In accordance with a further aspect of the present invention, there is provided a dielectric ceramic composition represented by the following chemical formula 3:
a
wt. % {
x
ZrO
2
−y
ZnO−
w
Nb
2
O
5
−z
TiO
2
}+c
wt. % ZnO—B
2
O
3
—SiO
2
based Glass Frit+
d
wt. %CuO  Chemical Formula 3
wherein, 5.0 mol %≦x≦45.0 mol %; 1.5 mol %≦y≦19.0 mol %; 1.5 mol %≦w≦19.0 mol %; 40.0 mol %≦z≦59.0 mol % with the proviso that x+y+w+z=100; 75.0≦a≦97.0; 3.0≦c≦25.0; and d≦5.0.
In accordance with still a further aspect of the present invention, there is provided a dielectric ceramic composition represented by the following chemical formula 4:
a
wt. % {
x
ZrO
2
−y
ZnO−
w
Nb
2
O
5
−z
TiO
2
}+b
wt. % (MgO, CoO, SiO
2
, Sb
2
O
3
, Sb
2
O
5
, MnO
2
, Ta
2
O
5
or combinations thereof)+
c
wt. % ZnO—B
2
O
3
—SiO
2
based Glass Frit  Chemical Formula 4
wherein, 5.0 mol %≦x≦45.0 mol %; 1.5 mol %≦y≦19.0 mol %; 1.5 mol %≦w≦19.0 mol %; 40.0 mol %≦z≦59.0 mol % with the proviso that x+y+w+z=100; 75.0≦a≦97.0; b≦1.5; 3.0≦c≦25.0; and d≦5.0)
DETAILED DESCRIPTION OF THE INVENTION
Based on ZrO
2
—ZnO—Nb
2
O
5
—TiO
2
with low dielectric loss and high dielectric constant (>45), the dielectric composition of the present invention comprises ZnO—B
2
O
3
—SiO
2
glass frit as a sintering aid, thereby exhibiting a high electric constant of 30 or more and low dielectric loss (Q>1,000 (at 3 GHz), Q≈1/tan &dgr;), and being able to be cofired with Ag electrode patterns.
To the composition, at least one oxide selected from the group consisting of MgO, CoO, SiO
2
, Sb
2
O
3
, Sb
2
O
5
, MnO
2
, and Ta
2
O
5
, and/or CuO may be further incorporated. In the dielectric composition, the oxide is used to improve dielectric properties while CuO acts as a sintering aid.
As described above, the ceramic composition of ZrO
2
—ZnO—Nb
2
O
5
—TiO
2
is low in dielectric loss and 45 or higher in dielectric constant and is sintered at 1,300° C. The high sintering temperature makes it impossible to sinter the ceramic composition with electrodes made of Ag whose melting point is 961° C.

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