Compositions: ceramic – Ceramic compositions – Titanate – zirconate – stannate – niobate – or tantalate or...
Reexamination Certificate
2001-01-22
2003-03-04
Koslow, C. Melissa (Department: 1755)
Compositions: ceramic
Ceramic compositions
Titanate, zirconate, stannate, niobate, or tantalate or...
C501S136000, C501S138000
Reexamination Certificate
active
06528445
ABSTRACT:
This application claims priority to Republic of Korea patent application 2000-68493 filed Nov. 17, 2000.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to a dielectric ceramic composition and, more particularly, to a dielectric ceramic composition controllable in temperature coefficient of resonant frequency and sinterable at low temperatures, suitable for use in planar or multilayer type electronic parts containing inner conductors, for the fabrication of which simultaneously sintering base materials and conductors is required. Also, the present invention is concerned with a method for manufacturing such a dielectric ceramic composition.
2. Description of the Prior Art
With great advances in electronic and communication technologies, apparatuses and equipments for embodying them have recently been miniaturized. To this miniaturization, stacking and chipping techniques of electronic parts make a great contribution. Generally, ceramic materials for use in electronic parts are divided into dielectrics and magnetics. Recently, particular pressure has been placed on electronic parts made of dielectrics to miniaturize.
Representative of the electronic parts to which stacking techniques are applied is a capacitor. Examples of multilayer type electronic parts for use in mobile communication terminals include filters, couplers, duplexers, oscillators and multichip modules (MCM). The multilayer type electronic parts, most portions of which are formed of multiplayer dielectrics and inner electrodes, are fabricated by laminating a dielectric into a tape, printing an inner electrode onto the dielectric laminate, stacking a plurality of laminates and firing the stack.
To be useful for multilayer type elements, accordingly, dielectrics must be capable of being sintered along with electrodes in addition to having dielectric properties suitable for application. Such dielectric requirements include high dielectric constant, low dielectric loss, and low dependency of resonant frequency modulation on temperature change and the like.
Materials suitable for the inner electrodes are silver, copper, nickel, palladium, platinum, gold and alloys thereof. Selection of one of the inner electrode materials is made depending on the sintering temperature and properties of the ceramic dielectric used and vice versa.
For example, silver (Ag), showing the lowest specific resistance (1.62×10
−4
&OHgr;cm) and being inexpensive, cannot be applied to ceramic dielectrics which must be sintered at 950° C. or higher because of its low melting point (961° C.). In spite of their high melting points, gold (Au), platinum and palladium (Pd) are restricted in their use because of high price. 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, causing the problem that, when thermally treated under such a low oxygen partial pressure, most dielectric ceramic compositions show highly increased dielectric loss and thus cannot be used as capacitors.
Ceramic dielectric compositions currently used in multilayer type electronic parts are, for the most part, based on BaTiO
3
, optionally added with oxide sintering aids or glass frits for reduction of sintering temperatures. Typically, these dielectric compositions range, in sintering temperature, from 1,100 to 1,300° C., as well as being resistant to reduction and having dielectric constants of several hundreds or higher. However, their great dielectric loss makes it difficult to apply them to the products which are used for high frequency band of MHz or higher. Additionally, the dielectric compositions suffer from the drawback of undergoing a dielectric constant fluctuation of as large as hundreds ppm/° C., which prevents them from being applied to temperature-stable capacitors or electronic parts for mobile communication.
Dielectric compositions known to be usable for multilayer type elements operable with frequencies of MHz or higher are exemplified by Cuo or V
2
O
5
-added BiNbO
4
and glass-added (Mg, Ca)TiO
3
, (Zr, Sn)TiO
4
or (BaO—TiO
2
—WO
3
). These compositions, however, have drawbacks of being not effectively sintered at a temperature lower than 1,000° C., being poor in dielectric properties at microwave frequencies, and showing large reactivity with electrode materials.
Another well-known dielectric composition is based on a BaO—TiO
2
—Nb
2
O
5
system, whose subtypes comprise BaTiNb
4
O
13
, Ba
3
Ti
4
Nb
4
O
21
and Ba
3
Ti
5
Nb
6
O
28
(see. “New low microwave dielectric ceramics in the BaO—TiO
2
—Nb
2
O
5
/Ta
2
O
5
system”, M. T. Sebastian, Journal of Materials Science; Materials in Electronics, Vol. 10 (1999), pp. 475-478). U.S. Pat. No. 4,767,732 discloses a high dielectric constant ceramic material having a high dielectric constant and a high insulation resistance obtained by mixing BaTiO
3
powder and oxides of Pb, Ba, Sr, Zn, Nb, Mg and Ti. These compositions Ba
3
Ti
4
Nb
4
O
21
and BaTiO
3
, in spite of having a dielectric constant and a quality factor (Q×f) amounting to as large as 55 and 9,500, respectively, is virtually impossible to apply to electronic parts which require high frequencies of microwave bands or high temperature stability for their operation because its temperature coefficient of resonant frequency is 100 ppm/° C. Furthermore, this publication does not describe low-temperature sintering properties of the composition.
SUMMARY OF THE INVENTION
With the problems encountered in prior arts in mind, the present invention has an object of providing a dielectric ceramic composition, which is controllable in temperature coefficient of resonant frequency and sinterable at low temperatures.
It is another object of the present invention to provide a dielectric ceramic composition with excellent dielectric properties suitable for use in planar or multilayer type elements operable with frequencies from MHz to GHz.
It is a further object of the present invention to provide a method for manufacturing such a dielectric ceramic composition.
Based on the present invention, there is provided a ceramic Composition comprising as a main component a compositions represented by
(1
−X
)Ba
3
Ti
4
Nb
4
O
21
−(
X
)ANb
2
O
6
wherein, X is a mole fraction between 0 and 1; and A is Ba or Sr.
A is Ba or Sr.
According to one aspect of the invention, the ceramic composition may further comprise at least one oxide selected from the group consisting of B
2
O
3
, CuO and ZnO, and or alternatively at least one additive selected from the group consisting of V
2
O
5
, SnO
2
, MgO, NiO, Sb
2
O
3
, Bi
2
O
3
and Ag
2
O.
The present invention further provides a method for manufacturing a dielectric ceramic, comprising the steps of: mixing oxide powders to give a composition composed of (1—x)Ba
3
Ti
4
Nb
4
O
21
—(x)Ba(or Sr)Nb
2
O
6
; drying and calcining the composition; milling the calcinated composition; molding the milled composition to give a molded body; and sintering the molded body.
In another aspect of the present invention, the process may further comprise the steps of adding the sintering aids and/or additive to the composition before calcination.
DETAILED DESCRIPTION OF THE INVENTION
The present invention contemplates a composite dielectric ceramic composition suitable for use in microwave bands, comprising two separate ingredients with different temperature coefficients of resonant frequency, one being of negative temperature coefficient of resonant frequency, the other of positive. As a dielectric ceramic with a negative dielectric constant, Ba
3
Ti
4
Nb
4
O
21
is used in the present invention. The other ceramic useful in the present invention is composed of BaNb
2
O
6
or SrNb
2
O
6
. Optionally, the composite dielectric ceramic composition comprises a sintering aid selected from the group consisting of B
2
O
3
, CuO and ZnO.
A temperature of as high as 1,200° C. is needed to sinter the Ba
3
Ti
4
Nb
4
O
21
—Ba(or Sr)Nb
2
O
6
-based composition (sometimes, “base composition”)
Hong Kug Sun
Jung Hyun-Woo
Kang Sang-Gu
Kim Dong-Wan
Kim Jeong-Ryeol
Hong Kug Sun
Koslow C. Melissa
Shanks & Herbert
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