Compositions: ceramic – Ceramic compositions – Titanate – zirconate – stannate – niobate – or tantalate or...
Reexamination Certificate
2000-03-15
2002-01-22
Brunsman, David (Department: 1755)
Compositions: ceramic
Ceramic compositions
Titanate, zirconate, stannate, niobate, or tantalate or...
C501S139000
Reexamination Certificate
active
06340649
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to composition of dielectric ceramics, in particular such composition of dielectric ceramics having a sintering property at low temperature, enabling to use, as an internal conductor, Ag or alloys containing a main component of Ag, and a method therefor.
2. Description of the Related Art
Recently, the growth of communication of those moving such as car telephones, pocket telephones and others is remarkable. In the communication of these moving ones, high frequency zone called as quasi microwaves of several 100 MHz to several GHz is used. Therefore, high frequency characteristics are made great account also in electronic devices as resonators, filters or capacitor to be used in the communication instruments of the moving ones. As to the recent popularization of the moving communication, miniaturization and low cost of the communicating instruments are important factors other than improvement of services, and are demanded also in regard to electronic devices.
For example, in materials for resonators, the following characteristics (1) to (4) are required for the using frequency to improve and miniaturize the high frequency characteristics.
(1) Specific dielectric constant is large: The resonator to be used nearly the microwave often utilizes a fact that the wave length is shortened in a dielectric substance in proportion to the inverse number of a square root of dielectric constant, and the length of the resonator can shorten the wave length in proportion of the reverse number of the square root of the dielectric constant.
(2) Q is large: For the materials of the microwave, Q to be defined with Q=1/tan &dgr; is used as valuation of dielectric loss, and that Q is large says the loss is small.
(3) Temperature change of the dielectric constant is small: The temperature change of the resonance frequency of the resonator or the filter is controlled to the utmost, and so it is desirous that the temperature change of the dielectric constant is small.
(4) The sintering at low temperature is possible: For realizing the miniaturization of electronic devices, parts of surface mount devices (SMD) holding conductive electrodes within interiors thereof have been changing to main streams. In this case, it is desirable to use Ag or Cu being low resistance as internal conductive electrodes for heightening the loss characteristics of the electronic device. But Ag or Cu have low melting points, and it is required that compositions for the dielectric ceramics may be sintered at temperature lower than their melting points. The matter of simultaneous sintering is also pointed out when Ag or Cu is made capacitor materials for temperature compensation.
As materials of dielectric ceramics for the microwave, compositions as BaO—4TiO
2
group or BaO-rare earth oxides-TiO
2
group are well known. In particular, as BaO—Nd
2
O
3
—TiO
2
group is high in the dielectric constant and the Q value, comprehensive studies have been made thereon. Of late years, the sintering at low temperature has been carried out in these compositions, and such technologies are described in patent 2613722 (calcining main components, followed by pulverizing until predetermined powder diameter, and adding sub-components thereto), Japanese patent No. 2781500, Japanese patent No. 2781501, Japanese patent No. 2781502, Japanese patent No. 2781503, and Japanese patent No. 2786977 (these Japanese patents use glass as sub-component), JP-A-5-234420, JP-A-6-211564, JP-A-6-223625, JP-A-7-69719, JP-A-8-55518, JP-A-8-55519, JP-A-8-167322, JP-A-8-167323, JP-A-8-167324, JP-A-8-208328, JP-A-8-208329 (these contain glass as a sub-component), JP-A-3-290359, JP-A-3-295854, JP-A-3-295855, JP-A-3-295856, JP-A-6-116023, JP-A-6-150719, JP-A-6-162822, JP-A-8-55518, JP-A-8-167322, JP-A-8-167323, JP-A-8-167324, JP-A-8-208328, JP-A-8-208329, JP-A-8-245262 (these contain Ge oxide as a sub-component), and other JP-A-61-56407, JP-A-2-44609, JP-A-5-97508, JP-A-6-116023, JP-A-8-157257, and JP-A-8-277161.
In almost all of them, BaO-rare earth oxides-TiO
2
are main components to which glass composition or glass composition and several kinds of sub-components are added capable of carrying out the sintering at low temperature. In addition, many of the dielectric materials contain PbO and Bi
2
O
3
in the main components or added components. This is why, since PbO and Bi
2
O
3
also have promoting effects of the sintering at low temperature together with an improving effect of the property such as increasing the dielectric constant, effects of both enable to provide the materials sintered at low temperature for high frequency.
Since the dielectric ceramics of BaO—Nd203—TiO2 group is as mentioned high in the dielectric constant and Q, and small in temperature coefficient of the dielectric constant, it is utilized for dielectric substance for microwave. The sintering at low temperature has recently been realized in BaO—Nd203—TiO2 group, and most of them contain at least one of PbO and Bi203 for improving the properties and promoting the sintering at low temperature.
However, environmental protection campaign of a global scale has lately been raised. Therefore, also in the fields of electronic parts, it is expected to reduce environmental contaminating substances as PbO, Bi
2
O
3
and others. When substances contain environmental contamination, treating facilities of waste liquid or special equipment are necessary in manufacturing processes, and also in view of production cost, it is desirous not to contain such environmental contaminating substances. Further, PbO, and Bi
2
O
3
are easily evaporated at high temperature, and ready for dispersing factors, and yet being neither PbO nor Bi
2
O
3
is desired.
Further, for most of the conventional composition of dielectric ceramics, as mentioned above, the glass composition is indispensable as additives for promoting the sintering, and therefore it is necessary to previously make predetermined glass, inviting cost-up by increasing a production step and enhancing unstable elements. Besides, since a limitation of composition for glass is added due to glazing, an optimum composition is not always realized and properties of dielectric ceramics might be deteriorated. On the other hand, studies have been made on dielectric ceramicss not added with glass, but since many of them necessitate the sintering temperature of 1000° C. or higher, there arises a problem that, for example, Ag cannot be used as an internal conductor.
In the conventional composition of dielectric ceramics, in case Ag as the internal conductor is sinterd, it is diffused into an interior of the dielectric substance. Since this Ag diffusion is caused by an Ag concentration gradient, the Ag concentration in the interior of the dielectric substance is not uniform, for example, the Ag concentration is high around the Ag conductor, while it is low in parts separate therefrom. When Ag is diffused in the dielectric substance, the dielectric properties are changed by the Ag concentration, and therefore electronic parts where Ag is the internal conductor will have such dielectric properties made different depending on the parts, causing inconveniences of non-uniform device property so that desired device properties could not be provided. By the Ag diffusion in the dielectric substance, the Ag amount is decreased in the internal conductor, thereby also causing inconveniences of non-uniform device properties so that desired device properties could not be provided.
In case the Ag diffusion amount from the internal conductor into the dielectric substance is much, there is generated a space between the internal conductor and the dielectric substance or caused a leading-in in a portion of the conductor for connecting with an external part, so that an inconvenience as disorder of conduction is caused. In particular, recently miniaturization of high frequency parts has rapidly been advanced, and in response to such conditions, the internal conductor has been made fine pattern or thin in heig
Fukuhara Aya
Kawata Tomoaki
Nakamura Akira
Sakurai Toshio
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