Compositions: ceramic – Ceramic compositions – Titanate – zirconate – stannate – niobate – or tantalate or...
Reexamination Certificate
2000-03-16
2002-01-01
Tucker, Philip (Department: 1712)
Compositions: ceramic
Ceramic compositions
Titanate, zirconate, stannate, niobate, or tantalate or...
C361S321100, C361S321200, C361S321400, C428S697000
Reexamination Certificate
active
06335301
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dielectric ceramic composition used in an electric device, such as a multi-layer chip capacitor, an electric device using the dielectric ceramic composition and a method of producing the electric device, particularly relates to a dielectric ceramic composition used in a multi-layer chip capacitor suitable for high frequencies.
2. Description of the Related Art
Heretofore, a variety of dielectric ceramic materials have been widely used as a material for a multi-layer chip capacitors. Since electric devices used in mobile communications, such as a cellular phones, are driven in high frequency ranges, development of dielectric materials suitable for high frequency ranges has been increasing.
As characteristics of a dielectric ceramic material used in high frequency ranges, it is desired to have an appropriate dielectric constant &egr;r, a large dielectric loss Q, a resonance frequency temperature coefficient TCf being close negatively and positively to 0 (NPO). For example, BaTi
4
O
9
+ReO based compositions and MgTiO
3
—CaTiO
3
based compositions, etc. have been developed as compositions fulfilling the above requirements.
However, the burning temperature of these compositions is extremely high at 1300 to 1400° C., so that Pd or Pd—Ag alloy, etc. which have a high melting point have to be used as an internal conductive metal inside a multi-layer chip capacitor.
Other than the above, development has been also made of CaZrO
3
—SrZrO
3
based materials with the assumption of being used as an internal conductor of Ni as disclosed in Japanese Examined patent Publication (Kokoku) No. 7-66693, however, the materials are burned at 1300 to 1400° C.
Also, development of CaSr—ZrTi—Mn based materials is disclosed in the Japanese Unexamined Patent Publication (Kokai) No. 60-131708. In this publication, a dielectric ceramic composition for a capacitor using Ni as a terminal electrode is disclosed. The burning temperature of the Ni terminal is 800 to 1000° C., while the ceramic composition is burned at 1350° C.
Since the above Pd, Ni, etc. have a high conductive resistance, when used as an internal electrode of a multi-layer chip capacitor, the ratio of an electrode loss becomes larger than that of a dielectric loss in a high frequency range. As a result, the Q value of the capacitor becomes smaller, it is not possible to make the most of the excellent high frequency characteristics that the dielectric materials originally have, and it has been difficult to use it in high frequency circuits.
Thus, such metals having a low conductive resistance as Cu and Ag have been proposed. When using Cu or Ag as an internal electrode, however, the burning temperature of the dielectric material must not be more than 1000° C. It is because when exceeding 1000° C., the metals are exposed to the temperature ranges higher than or closer to their melting points, so that defaults are caused due to particles melting or becoming ball-shaped, and thus the metals cease to function as electrodes.
In the case of dielectric ceramic composition disclosed in the above Japanese Examined patent Publication (Kokoku) No. 7-66693, it was difficult to attain a burning temperature of 1000° C. or less while maintaining the desired electric characteristics.
SUMMARY OF THE INVENTION
An object of the present invention is to overcome the above disadvantages by providing a dielectric ceramic composition able to be burned at a relatively low temperature of 1000° C. or less both in air and in a non-oxidizing atmosphere, having a high Qf value and a small temperature coefficient TCf.
To attain the above object, an electric ceramic composition of the present invention, comprises a main component expressed by a composition formula [SrZrO
3
]
x
+[CaTiO
3
]
(1−x)
wherein “x” indicating a mole ratio in the composition formula satisfies 1.00≧x≧0.60 and a sub component including at least B
2
O
3
, SiO
2
and Li
2
O and satisfies
1.80>a≧0.25
1.80>b≧0.20
1.80>c≧0
1.10>d≧0
6.30>e≧0.05
10.00>a+b+c+d+e≧0.50
Where a content ratio of B
2
O
3
is “a” parts by weight, a content ratio of SiO
2
is “b” parts by weight, a content ratio of ZnO is “c” parts by weight, a content ratio of Al
2
O
3
is “d” parts by weight and a content ratio of Li
2
O is “e” parts by weight with respect to 100 parts by weight of said main component.
The dielectric ceramic composition of the present invention is able to be burned at a relatively low temperature of 1000° C. or less, has a high Qf value (for example Qf=2000 or more), a desired dielectric constant (for example &egr;r=24 to 80) and a temperature coefficient TCf which is +300 to −80 ppm/° C. Accordingly, the dielectric ceramic composition can be preferably applied to a multi-layer chip capacitor having Cu, Ag, etc. as an internal conductor, and particularly applied to an electric devices used in high frequency regions.
Further, in the case of a dielectric ceramic composition wherein the value of the above “x” satisfies 1.00≧x≧0.90, the Qf value further increases (for example Qf=4000 or more) and the temperature coefficient TCf becomes +100 to −80 ppm/° C., so that the characteristics of the dielectric ceramic composition become still better.
An electric device according to the present invention comprises an internal electrode layer and a dielectric layer, wherein
said dielectric layer comprises:
a main component expressed by [SrZrO
3
]
x
+[CaTiO
3
]
(1−x)
, wherein “x” indicating a mole ratio in the composition formula satisfies 1.00≧x≧0.60; and
a sub component including at least B
2
O
3
, SiO
2
and Li
2
O,
and satisfies:
1.80>a≧0.25
1.80>b≧0.20
1.80>c≧0
1.10>d≧0
6.30>e≧0.05
10.00>a+b+c+d+e≧0.50
Where a content ratio of B
2
O
3
is “a” parts by weight, a content ratio of SiO
2
is “b” parts by weight, a content ratio of ZnO is “c” parts by weight, a content ratio of Al
2
O
3
is “d” parts by weight and a content ratio of Li
2
O is “e” parts by weight with respect to 100 parts by weight of said main component.
Preferably, said internal electrode layer contains Cu and/or Ag.
A method of producing an electric device according to the present invention, comprises the steps of:
preparing a material of a main component expressed by a composition formula [SrZrO
3
]
x
+[CaTiO
3
]
(1−x)
wherein “x” indicating a mole ratio satisfies 1.00≧x≧0.60,
preparing a material of a sub component including at least B
2
O
3
, SiO
2
and Li
2
O, and satisfying
1.80>a≧0.25
1.80>b≧0.20
1.80>c≧0
1.10>d≧0
6.30>e>0.05
10.00>a+b+c+d+e≧0.50
where a content ratio of B
2
O
3
is “a” parts by weight, a content ratio of SiO
2
is “b” parts by weight, a content ratio of ZnO is “c” parts by weight, a content ratio of Al
2
O
3
is “d” parts by weight and a content ratio of Li
2
O is “e” parts by weight with respect to 100 parts by weight of said main component;
obtaining a dielectric layer paste by mixing the material of the main component with the material of the sub component;
obtaining an internal electrode layer paste;
preparing a green chip to be an element body after being burned having a dielectric layer and an internal electrode layer by using said dielectric layer paste and internal electrode layer paste; and
burning said green chip at a temperature of 900 to 1000° C.
Preferably, Cu and/or Ag is contained as an electroconductive material when preparing the internal electrode layer paste.
Note that in this specification, respective oxides composing the main component and the sub component are expressed by a stoichiometry composition, but oxidizing conditions of the respective oxides may be outside of the stoichiometry composition. Note that the above ratios of the respective sub components are obtained by measuring res
Kikuchi Tatuya
Tanaka Hitoshi
Oliff & Berridg,e PLC
TDK Corporation
Tucker Philip
LandOfFree
Dielectric ceramic composition, electric device and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Dielectric ceramic composition, electric device and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dielectric ceramic composition, electric device and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2819946