Manufacture method of dielectric ceramic composition

Details Manufacture method of dielectric ceramic composition Manufacture method of dielectric ceramic composition

2001-06-04

2003-04-08

Brunsman, David (Department: 1755)

Compositions: ceramic

Ceramic compositions

Titanate, zirconate, stannate, niobate, or tantalate or...

C501S139000

Reexamination Certificate

active

06544916

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a method of producing a dielectric ceramic composition having resistance to reduction, a specific permittivity of 1000 or more, a capacitance-temperature characteristic satisfying the X8R characteristic (within −55 to 150° C., within &Dgr;C±15%) of the EIA standard, small dielectric loss, high permittivity, high insulation resistance and an excellent high temperature accelerated lifetime characteristic.
BACKGROUND ART
A multilayer ceramic capacitor is widely used as a compact, large capacitance, highly reliable electronic device, and the number used in one electronic device reaches large. In recent years, along with devicees becoming compact and high in performance, demands for still more compact, larger capacitance, lower price and more reliable multilayer ceramic capacitor have been getting furthermore stronger.
As a dielectric ceramic composition having a high permittivity and a flat capacitance-temperature characteristic, there is known a composition wherein BaTiO
3
is a main component and Nb
2
O
5
—Co
3
O
4
, MgO—Y, a rare-earth element (Dy, Ho, etc.), Bi
2
O
3
—TiO
2
, etc. are added thereto. The temperature characteristic of the dielectric ceramic composition containing BaTiO
3
as a main component has difficulty in satisfying the R characteristic (&Dgr;C=within ±15%) of the capacitance-temperature characteristic in a high temperature region of 130° C. or more because the Curie temperature of BaTiO
3
is near 120° C. Therefore, Batio
3
based material of high permittivity could fulfill only the X7R characteristic (−55 to 125° C., &Dgr;C=within ±15%) of the EIA standard.
In recent years, a multilayer ceramic capacitor has come to be used in a variety of electronic devices, such as an engine electronic control unit (ECU) installed in an engine room, a crank angle sensor, anti-lock brake system (ABS) module in vehicles. Since these electronic devices are for stabilizing engine control, drive control and brake control, temperature stability of the circuit is required to be good.
An environment in which these electronic devices are used is considered that the temperature becomes about −20° C. or lower in winter in cold districts and the temperature rises up to about +130° C. or more after starting the engine in summer. Recently, the trends are to reduce wire harnesses connecting the electronic device with an apparatus as its object to control and the electronic device is provided outside a vehicle in some cases, so the environment has been getting more severe for the electronic device. Accordingly, a conventional dielectric ceramic composition having the X7R characteristic is unable to cope with such an application.
Also, as a capacitor material for temperature compensation excelling in the temperature characteristic, (Sr,Ca)(Ti,Zr)O
3
base, Ca(Ti,Zr)O
3
base, Nd
2
O
3
—2TiO
2
base, La
2
O
3
—2TiO
2
base, etc. are generally known, however, since these compositions have a very low specific permittivity (generally, not more than 100), it is substantially impossible to produce a capacitor having a large capacitance.
On the other hand, in a dielectric ceramic composition containing BaTio3 as a main component, there has been a proposal to shift the Curie temperature to a high temperature side by substituting Ba in BaTiO
3
by Bi, Pb, etc. so as to satisfy the X8R characteristic (the Japanese Unexamined Patent Publication Nos. 10-25157, 9-40465). Also, there has been proposed to satisfy the X8R characteristic by selecting a composition of BaTiO
3
+CaZrO
3
+ZnO+Nb
2
O
5
base (the Japanese Unexamined Patent Publication Nos. 4-295048, 4-292458, 4-292459, 5-109319 and 6-243721). In any of these composition bases, however, since Pb, Bi and Zn easy to be evaporated and scattered are used, firing in an oxidizing atmosphere, such as in an air, becomes premise. As a result, there is a problem that inexpensive Ni or other base metals cannot be used as internal electrodes in the capacitor and expensive rare metals like Pd, Au, Ag, etc. have to be used.
To solve the problem, the present inventors have proposed a dielectric ceramic composition wherein Ni or Ni alloy can be used as internal electrodes in a capacitor (the Japanese Unexamined Patent Publication Nos. 10-2206, 11-206291 and 11-206292).
According to these techniques, by making rare-earth elements, such as Sc, Er, Tm, Yb, Lu, etc., contained in the dielectric ceramic composition, it becomes possible to shift the Curie temperature to the high temperature side and to flatten the capacitance-temperature change rate at the Curie temperature or higher, reliability (high temperature load lifetime, capacitance time change, etc.) can be improved.
However, a second phase containing a rare-earth element as a main component is apt to be segregated in the dielectric when increasing an amount of rare-earth element to be added to the dielectric ceramic composition. Due to the segregation of the second phase, strength of the dielectric was improved, but it was confirmed by the present inventor that the segregated second phase came to have about the same thickness as that of the dielectric layer of the multilayer capacitor depending on the thickness of the dielectric layer, and reliability of the capacitor was liable to be declined. Also, it was confirmed by the present inventors that a product (CR product) of the permittivity and the insulation resistance were apt to decline along with an increase of the amount of the second layer segregated in the dielectric layer.
Also, multilayer ceramic capacitor to be installed in vehicles has made progress in attaining large capacitance and compact size, and the trends are that the thickness of the dielectric layer is getting thinner. Therefore, particularly, in a dielectric ceramic composition wherein rare-earth element is added to dielectric ceramic composition, a technique to control the size and amount of the second phase to be segregated becomes necessary.
To improve reliability of a dielectric ceramic composition having the X7R characteristic, there is a proposal of a method of calcining BaTiO
3
as a main material and additives in advance (the Japanese Examined Patent Publication No. 7-118431). In the technique disclosed in the publication, it is considered that the composition of the finally composed dielectric composition becomes (Ba, Mg, Ca, Sr, Zn)(Ti, R)O
3
+(Ca, Ba)ZrO
3
+glass. Then, when assuming R=Sc, Y, Gd, Dy, Ho, Er, Yb, Tb, Tm and Lu, calcination of BaTiO
3
and the additives is performed so that the mole ratio expressed by (Ba+Mg+Ca+Sr+Zn)/(Ti+Zr+R) comes down to the range of 1.00 to 1.04.
In this method, however, it is considered as premise that alkaline earths (Mg, Ca, Sr, Ba) dissolves in a Ba site and rare-earth elements (R=Sc, Y, Gd, Dy, Ho, Er, Yb, Tb, Tm, Lu) dissolves in a Ti site. Thus, along with an increase of an amount of rare-earth elements to be added, it is necessary that an amount of the alkaline earth to be added is inevitably increased. Also, when the mole ratios in this composition base are specified as above, the high temperature load lifetime (IR lifetime) as the X8R characteristic ends up deteriorating. While, there arises a problem of deterioration in sintering when alkaline earth is increased in accordance therewith. Furthermore, Zn has a problem that it is easy to evaporate.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a method of enabling to produce a dielectric ceramic composition preferably used as a dielectric ceramic composition for a multilayer chip capacitor wherein base metals like Ni, Ni alloy, etc. can be used for internal electrodes, segregation of different phases other than the main composition is controlled, the fine configuration of the dielectric is controlled, the capacitance-temperature characteristics satisfies the X8R characteristic, dielectric loss is small, permittivity and insulation resistance are high and the high temperature accele

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