Compositions: ceramic – Ceramic compositions – Titanate – zirconate – stannate – niobate – or tantalate or...
Reexamination Certificate
2001-09-05
2003-09-16
Brunsman, David (Department: 1755)
Compositions: ceramic
Ceramic compositions
Titanate, zirconate, stannate, niobate, or tantalate or...
C501S135000, C264S615000, C264S618000, C361S321400
Reexamination Certificate
active
06620750
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dielectric ceramic composition and a method for manufacturing multilayered components using the same. More specifically, the present invention is directed to a dielectric ceramic composition having dielectric properties suitable for high frequency regions such as microwave and millimetric wave, a low dielectric loss, a large dielectric constant and temperature stability, in which the dielectric composition can be sintered at low temperature and thus simultaneously baked with metal electrodes, such as silver, copper, silver/palladium, so being applicable to electronic parts, including resonators, multilayered ceramic capacitors, filters, dielectric substrate materials for monolithic IC (MIC), and dielectric waveguide materials and the like, and a method for manufacturing multilayered components using the dielectric ceramic composition.
2. Description of the Prior Art
Along with great advances in electronic and communication technologies, the hardware for embodying them has also been miniaturized. This miniaturization is due in part to new stacking and chipping techniques. Recently, because of the development of communication means using microwave bands, such as mobile phones and satellite broadcasting, there is continuing pressure and demand in the market place for further miniaturization of dielectrics components.
An example of the components to which stacking techniques are applied is a capacitor. Examples of stacked type components for use in mobile communication terminals include filters, couplers, duplexers, oscillators and multichip modules (MCM).
The stacked type components are generally composed of multilayered dielectrics and inner electrodes which are fabricated by laminating a dielectric into a thin tape, printing an inner electrode onto the dielectric laminate, stacking many laminates and firing the stack.
Suitable materials for the composition of inner electrodes include silver, copper, nickel, palladium, platinum, gold and alloys thereof. The selection of inner electrode materials is determined based on sintering temperature and the properties of the ceramic dielectrics which are sintered therewith.
In this regard, a silver (Ag) electrode, exhibiting the lowest specific resistance (1.62×10
−4
&OHgr;m) and being inexpensive, cannot be applied to ceramic dielectrics which must be sintered at 950° C. or higher, because of silver's low melting point (mp.) of 961° C. Meanwhile, gold (Au), platinum (Pt) or palladium (Pd) have low melting points, but are disadvantageous in terms of their high cost, so that the use of these materials is restricted. As for copper (Cu) or nickel (Ni) electrodes, their very poor oxidation resistance requires sintering at an oxygen partial pressure as low as about 10
−9
atm. The low pressure associated with thermally treating Nickel or copper electrodes under low oxygen, partial pressure causes most dielectric ceramic compositions to show highly increased dielectric loss, and therefore cannot be used as capacitors.
To be useful for stacked type components, dielectrics must be capable of being sintered along with electrodes in addition to having dielectric properties suitable for application. Such dielectric requirements include: 1) A high dielectric constant (∈
r
); 2) A quality factor (Qxf); and 3) A low dependency of resonance frequency modulation (&tgr;
f
) as a function of temperature change. Typically, these dielectric compositions are composed of BaO—TiO
2
, BaO—ReO—TiO
2
(ReO is oxide of rare-earth elements), MgTiO
3
—CaTiO
3
. BaO—TiO
2
has a high dielectric constant of 37-40, and a large quality factor (Qxf) of 30,000. However, in single-phase, BaO—TiO
2
is not capable of achieving a temperature coefficient corresponding to a resonant frequency of zero. Further problems include the fact that the dielectric constant is changed according to the composition, and further, there is a high temperature dependency of the dielectric constant modulation. Because of these inherent properties, the temperature coefficient of resonant frequency of low values cannot be stably maintained, while keeping a high dielectric constant and low dielectric loss.
On the other hand, BaO—ReO—TiO
2
types, including BaO—Nd
2
O
3
—TiO
2
or BaO—Sm
2
O
3
—TiO
2
, have a high dielectric constant of 50-80, and stable temperature coefficients of resonant frequency, but are disadvantageous based on low Qxf values of 5,000 or lower. In MgTiO
3
—CaTiO
3
, the value of Qxf is 30,000 or higher, the temperature coefficient of resonant frequency is approximately zero, the dielectric constant is within the range of 16-25.
Ceramic dielectric compositions in current use in stacked type components are, for the most part, composed primarily of BaTiO
3
, by itself or in composition with oxide-sintering aids, such as Bi
2
O
3
, or glass frits, for decreasing sintering temperatures. Typically, the sintering of temperatures these conventional dielectric compositions range from about 1,100 to about 1,300° C. Further, these dielectric compositions are resistant to reduction and possess dielectric constants with values of several hundred or higher. Their great dielectric loss, however makes it difficult to apply them in designs where a frequency band of 1 MHz or higher is used. Additionally, the dielectric compositions suffer from the drawback of undergoing a dielectric constant fluctuation of as large as several hundred ppm/° C., which renders them unusable as temperature-stable capacitors or components for mobile communication devices.
Dielectric compositions known to be usable for stacked type components, operable with frequencies of 1 MHz or higher, are exemplified by CuO or V
2
O
5
-added Bi
2
O
3
—CaO—Nb
2
O
5
and glass-added (Mg, Ca)TiO
3
, (Zr, Sn)TiO
4
or (CaO—ZrO
2
). CuO or V
2
O
5
added Bi
2
O
3
—CaO—Nb
2
O
5
compositions may be sintered at 900° C., possess a dielectric constant of 40 or higher, and a quality factor of 18,000 or higher. In addition, Japanese Laid-Open Patent Application No. Hei. 11-34231 and U.S. Pat. No. 5,350,639 relate to the manufacture of chip type stacked capacitors making use of low melting point electrodes including Ag and Cu, and dielectric resonators using strip lines.
Japanese Laid-Open Patent Application No. Hei. 9-315859 discloses that CaO—ZrO
2
is added with alkaline earth-metal compounds including boron (B), lithium (Li) and sodium (Na), and thus can be sintered at low temperatures in the range of about 900° to about 1,200° C. These compositions, however, cannot be effectively sintered at a temperature of 1,000° C. or lower, possess poor dielectric properties at microwave frequencies, and exhibit excess reactivity with electrode materials.
SUMMARY OF THE INVENTION
It is, accordingly, an abject of the present invention to provide a dielectric ceramic composition, which possesses excellent temperature stability, low temperature sintering properties, and a high dielectric quality factor at low dielectric bands.
Another object of the present invention is to provide a method for manufacturing multilayered components using the dielectric composition.
In one aspect of the present invention, there is provided a dielectric ceramic composition comprising (A) at least one oxide selected from the group consisting of La
2
O
3
, Nd
2
O
3
, Al
2
O
3
and Y
2
O
3
, and (B) at least one oxide selected from the group consisting of Nb
2
O
5
, Ta
2
O
5
, at a molar ratio of 1:1, and being represented by the general formula:
A′
x
A″
1−x
B′
y
B″
1−y
O
4
(wherein, A′ and A″ represent elements selected from the group consisting of La, Nd, Y and Al; B′ and B″ represent elements selected from the group consisting of Nb and Ta; and x and y represent mole fractions, each in the range of 0≦x≦1.0 and 0≦y≦1.0, respectively).
As such, the dielectric ceramic composition may further comprise at least one sintering aid selected from the group consisting of B
2
O
3
, CuO, ZnO and B
Kim Dong-Wan
Kim Jin-Young
Kwon Do-Kyun
Park Jong-Sung
Brunsman David
Hong Kook-Sun
Shanks & Herbert
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