Compositions – Electrically conductive or emissive compositions – Metal compound containing
Reexamination Certificate
1995-12-26
2002-03-12
Talbot, Brian K. (Department: 1762)
Compositions
Electrically conductive or emissive compositions
Metal compound containing
C252S514000, C029S610100, C427S101000, C427S126200, C427S126300, C427S376200
Reexamination Certificate
active
06355188
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention:
The present invention relates to a resistive material, a resistive paste which can be fired in a neutral or reducing atmosphere, and a resistor to be formed by the use of the resistive paste.
2. Description of the Related Art
In general, a ceramic substrate comprising alumina, zirconia or the like has circuit patterns for electrodes, resistors, etc., in order that various electronic parts can be mounted thereon. Electrodes (electrode patterns) are generally formed on the substrate by screen-printing a noble metal paste comprising silver, a silver-palladium alloy or the like followed by firing the thus-printed paste in air.
However, since a noble metal paste such as that mentioned above is not only expensive but also problematic in its migration resistance, the tendency for such an expensive noble metal paste to be replaced by a base metal paste comprising, as the conductive component, copper, nickel, aluminum or the like has become accepted in this technical field. Such a base metal paste can be screen-printed on a substrate and then fired in a neutral or reducing atmosphere to give an inexpensive and good electrode pattern.
In this case, it is desirable that the resistive paste which is to form resistors (resistor patterns) on the substrate, by which the plural base electrodes as formed by firing the printed base metal paste are connected with each other, can also be fired in a neutral or reducing atmosphere.
Therefore, various resistive pastes that can be fired in a neutral or reducing atmosphere to form resistors (resistor patterns) have heretofore been proposed. Such resistive pastes includes, for example, resistive pastes comprising LaB
6
such as those described in Japanese Patent Publication Nos. 59-6481 and 58-21402, resistive pastes comprising NbB
2
such as those described in Japanese Patent Laid-Open No. 63-224301, resistive pastes comprising solid solutions of Nb
x
La
1−x
B
6−4x
such as those described in Japanese Patent Laid-Open No. 2-249203, etc.
However, conventional resistive pastes such as those mentioned above are problematic in that, when they are desired to have a resistance value that is variable within a broad range by varying the mixing ratio of the resistive material consisting the paste to glass frit to be added thereto, even a slight variation in the amount of the glass frit in the paste often results in a rapid variation in the resistance value of the paste (that is, the resistance value of the paste greatly depends on the composition of the paste) and therefore the reproducibility of the desired resistance value of the paste is poor. Therefore, such conventional resistive pastes are still problematic in that they can be formed into practicable resistors having a resistance value only within a narrow range between 10 &OHgr;/square and 10 K&OHgr;/square.
Apart from the above, other resistive pastes comprising a resistive material of RuO
2
, SrRuO
3
, CaRuO
3
or the like have also been proposed. However, resistive pastes comprising RuO
2
are problematic in that, when they are fired in a neutral or reducing atmosphere, RuO
2
is reduced to Ru metal with the result that they cannot be formed into resistors. Resistive pastes comprising SrRuO
3
or CaRuO
3
are also problematic in that, if the proportion of glass frit to be therein is increased more than a certain degree, the resistance value of the pastes suddenly becomes too great and therefore the reproducibility of the desired resistance value of the pastes is extremely poor.
SUMMARY OF THE INVENTION
The present invention seeks to solve the above-mentioned problems in the prior art and to provide a resistive paste which can be fired in a neutral or reducing atmosphere to surely give resistors having any desired resistance values within a broad range including values of even greater than 10 K&OHgr;, a resistive material which constitutes the resistive paste, and a resistor which can be formed by the use of the resistive paste and which can realize resistance values within a broad range while the reproducibility of the realizable resistance values is good.
The resistive material which the present invention provides so as to attain the above-mentioned object is characterized in that it has a composition of a general formula:
Ca
x
Sr
1−x
RuO
3
wherein x is from 0.25 to 0.75 moles.
The resistive paste which the present invention also provides so as to attain the above-mentioned object is characterized in that it comprises a solid component consisting of from 5 to 65% by weight of the resistive material and from 35 to 95% by weight of a non-reducible glass frit and an organic vehicle.
The resistor which the present invention also provides so as to attain the above-mentioned object is characterized in that it is formed by coating the resistive paste on a substrate and then firing it thereon.
REFERENCES:
patent: 4536328 (1985-08-01), Hankey
patent: 4814107 (1989-03-01), Steinberg
patent: 4865877 (1989-09-01), Yamaguchi et al.
patent: 5036027 (1991-07-01), Watanabe et al.
patent: 5264156 (1993-11-01), Gora et al.
patent: 5345212 (1994-09-01), Brown
patent: 5470668 (1995-11-01), Wu et al.
patent: 5550361 (1980-12-01), None
patent: 58-21402 (1983-04-01), None
patent: 59-6481 (1984-02-01), None
patent: 63-224301 (1988-09-01), None
patent: 2249203 (1990-10-01), None
patent: 4125901 (1992-04-01), None
Materials Research Society Symposium Proceedings, San Francisco, CA, vol. 341, Apr. 5-7, 1994, pp. 229-240, XP000608066 EOM C B et al., “Epitaxial Thin Films and Heterostructures of Various Isotropic Metallic Oxides for Device Application”.
Nagata Keisuke
Tani Hiroji
Murata Manufacturing Co. Ltd.
Ostrolenk Faber Gerb & Soffen
Talbot Brian K.
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