Low-fire microwave dielectric compositions

Details Low-fire microwave dielectric compositions Low-fire microwave dielectric compositions

1999-04-28

2001-10-30

Jenkins, Daniel J. (Department: 1742)

Compositions: ceramic

Ceramic compositions

Glass compositions, compositions containing glass other than...

C501S032000

Reexamination Certificate

active

06309993

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to dielectric ceramic compositions, especially to dielectric compositions for use in microwave dielectric ceramic devices. The dielectric composition of the present invention can be densified at low temperatures to provide ceramic devices with a high dielectric constant and a high quality factor.
BACKGROUND OF THE INVENTION
Recently, microwave dielectric ceramics have received increasing attention because of their applications in microwave resonators and filters where their high dielectric constant and high quality factors are required. To meet the requirement of small, thin, light mobile wireless communication systems, multilayer ceramic devices cofired with low loss conductors such as silver and copper are desired. This is also the major purpose of the present invention disclosure.
There are various microwave ceramic materials such as TiO
2
, Ba2Ti
9
O
20
, BaTi4O
9
, ZrO
2
—SnO
2
—TiO
2
, Ba(Zn
1/3
Ta
2/3
)O
3
and (Ba,Pb)Nd
2
Ti
5
O
4
. However, all these materials have sintering temperatures above 1300° C. and thus cannot be cofired with highly conductive metals, such as Ag and Cu. Several approaches can be taken to reduce the densification temperature of the above ceramic dielectric systems below 1000° C. or less, such as by using fine powders, adding sintering flux or low-softening glass. Adding a low-softening borosilicate glass to pure TiO
2
was chosen in the present invention.
U.S. Pat. No. 5,449,652 discloses a microwave dielectric ceramic composition comprising Bi
(2−x)
(Zn
(2+y)/3
Nb
(4/3)
)O
(7−3x/2+y/3)
wherein 0.24<x<0.333, 0.120<y<0.3; and Bi
(1−z)
Ca
(z)
(Zn
(2+y)/3
Nb
(4/3)
)O
(7−3x/2+y/3+xz/−z)
wherein 0<x<0.667, 0<y<0.30, 0<z<0.2. The microwave dielectric ceramic composition have properties including a dielectric constant(@ 7 GHz) of 100, quality factor (@ 7 GHz) of 7000 and a temperature coefficient of 10 ppm/° C.
U.S. Pat. No. 4,674,152 describes a ceramic composition with a low dielectric constant which comprises 50-95 wt % crystallizable glass and 5-50 wt % ceramic filler. The dielectric system has a dielectric constant of 5.1-6.0. The crystallizable glass consists of 5-20 wt % lithium oxide, 60-90 wt % silicon dioxide, 1-10 wt % aluminum oxide, and 1-5 wt % alkaline metal oxide other than lithium oxide. The ceramic fillers include silicon dioxide and aluminum oxide.
U.S. Pat. No. 4,755,490 describes a ceramic composition with a low dielectric constant which comprises 10-50 wt % alumina, 0-30 wt % fused silica, and 50-60 wt % of a frit comprised of 4 wt % CaO, 12 wt % MgO, 29 wt % B
2
O
3
and 42 wt % SiO
2
. The dielectric composition has a sintering temperature below 1000° C., a dielectric constant of 4.5-6.1, and a linear thermal expansion coefficient of 3.9-4.2×10
−6
K
−1
.
U.S. Pat. No. 5,415,945 describes a ceramic composition with a high dielectric constant which comprises 75-85 mol % Pb(Ni
1/3
Nb
2/3
)O
3
+0-15 mol % PbTiO
3
+5-16.5 mol % Pb(Zn
1/2
W
1/2
)O
3
+Pb(Cu
1/3
Nb
2/3
)O
3
. The composition has a sintering temperature of 1000° C. and a dielectric constant of 1000-4000.
U.S. Pat. No. 5,262,368 describes a ceramic composition with a high dielectric constant which comprises BaTiO
3
, BaCuO
2
, WO
3
and MoO
3
. The system has a sintering temperature of 1150° C., a dielectric constant of 2000-3000 (1 KHz) and a dielectric loss of 2.5%-16% (1 KHz).
U.S. Pat. No. 5,461,014 describes a ceramic composition with a high dielectric constant which comprises Pb(Mg
1/3
Nb
2/3
)O
3
and BaCuO
2
. The system has a sintering temperature of 1050° C., a dielectric constant of 7000-8000 (1 KHz) and a dielectric loss less than 3%.
Taiwan Patent Publication No. 159830 describes a ceramic composition with a high dielectric ceramic composition which is comprises Pb(Mg
1/3
Nb
2/3
)O
3
—PbTiO
3
—Pb(Zn
1/3
Nb
2/3
)O
3
. The system has a sintering temperature of less than 1000° C. and a dielectric constant of 8000-10000.
In view of the above development, it is obvious that ceramic materials which have a low sintering temperature, a high dielectric constant and a high quality factor (i.e. low loss) are needed in the industry. The present invention discloses ceramic compositions which meet the above requirements.
SUMMARY OF THE INVENTION
The present invention relates to a dielectric composition which can be densified at reduced temperatures to provide microwave dielectric ceramic devices with a high dielectric constant and a high quality factor. Since the ceramic composition of the present invention can be densified at reduced temperatures, the composition can be cofirable with conductors having a low melting point and low electrical resistance such as Ag, Au and Cu.
DETAILED DESCRIPTION OF THE INVENTION
It is commonly known that pure TiO
2
ceramics has desirable microwave properties, such as a high dielectric constant of 100 and a high quality factor in the range of 10,000 at the microwave frequencies. Dense pure TiO
2
ceramic cannot be obtained by sintering at temperature below approximately 1100° C. When such materials are used for the manufacture of multilayer ceramic devices, this high sintering temperature and the necessary presence of oxygen entails the use of electrodes made from expensive precious metals such as silver-palladium. A significant reduction in the manufacturing cost of such ceramic devices can be made by the substitution of pure silver for the silver-palladium in the electrodes. This requires the sintering temperature of multilayer ceramic devices below 950° C. To achieve this reduction in processing temperatures, a low-softening-point borosilicate glass (BSG) is added to pure TiO
2
.
Specifically, the present invention primarily relates to a dielectric composition comprising two ceramic components, borosilicate glass (BSG) and TiO
2
ceramic. The ratio of the two ceramics is not particularly limited, and can vary depending on the required properties of the products to be made. A preferred ratio is 20-90 vol % BSG and 10-80 vol % TiO
2
ceramic, and an even more preferred ratio is 20-60 vol % BSG and 40-80 vol % TiO
2
ceramic.
The borosilicate glass (BSG) used in the invention is regarded as glass phase, which has a softening temperature between 600 and 850° C. The term “glass” is used herein to describe ceramic compositions that melt and form glassy phase at a temperature below 1000° C. The BSG suitable for use in the invention consists essentially of, as the major components, 10-40 wt % of B
2
O
3
and 90-60 wt % of SiO
2
; and as the minor components, 0.1-4 wt % of Al
2
O
3
and 0.1-4 wt % of alkali metal oxides such as K
2
O, Na
2
O, Li
2
O, or a mixture thereof TiO
2
ceramic is defined as a “high sintering temperature ceramic phase” in the present invention. A preferred crystalline phase of TiO
2
is anatase rather than rutile.
The ceramic composition of the invention can be fabricated into high-frequency multilayer ceramic devices as follows: (a) preparing a slurry of (i) 70-85% by weight of a ceramic composition composed of 20-90 vol % BSG and 10-80 vol % TiO
2
ceramic, and (ii) 30-15% by weight of organic carriers including an organic binder; (b) casting the slurry to form a green sheet; (c) printing conductive pastes onto the green sheet; (d) laminating together a plurality of printed green sheets to form a multilayer ceramic green compact; (e) subjecting the multilayer ceramic green compact to binder burnout; and (f) sintering the multilayer ceramic green compact in air.


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patent: 4642148 (1987-02-01), Kurihara et al.
patent: 4939021 (1990-07-01), Aoki et al.
patent: 5786288 (1998-07-01), Jean
patent: 5801108 (1998-09-01), Huang et al.
patent: 5821181 (1998-10-01), Bethke et al.
patent: 5872071 (1999-02-01), Jean et al.
patent: 5898359 (1999-04-01), Ellis
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Condensed Chemical Dictionary, 10th ed., Van Norstr

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