Dielectric ceramic composition and laminated ceramic parts

Description Submit all comments and votes

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a temperature compensating dielectric ceramic composition, and laminated ceramic parts such as a laminated ceramic condenser and a laminated LC filter, each of which is formed by using such a temperature compensating dielectric ceramic composition.

2. Description of the Related Art

Conventionally, a temperature compensating ceramic condenser has been used as one of widely used electronic parts in various electronic devices in order to effect desired turning, oscillating and the like. Meanwhile, it has been demanded that the temperature compensating ceramic condenser be made compact in size, its dielectric loss should be small and its dielectric property be stable. As dielectric ceramic parts capable of satisfying the above requirements, it has been demanded that they should have a large relative dielectric constant and a small dielectric loss (namely, a large Q value) although its size is required to be small.

As such a desired dielectric ceramic mentioned above, there has been suggested a series of BaO--TiO.sub.2 dielectric ceramic composition (H. M. O'Brayan, J. Am, Ceram. Soc. 57(1974) 450; Japanese Examined Patent Publication 58-20905). Although a laminated ceramic condenser formed by using these dielectric ceramic compositions has been in actual use, since the sintering temperature involved in the manufacturing of such a product is as high as 1300 to 1400.degree. C., its internal electrode has to be made by a noble metal such as palladium (Pd) and platinum (Pt) capable of resisting such high temperature.

As some dielectric ceramic compositions which can be sintered at a relatively low temperature during their manufacturing processes, Japanese Unexamined Patent Publication No. 8-239262 has suggested a dielectric ceramic composition containing BaO--TiO.sub.2 --Nd.sub.2 O.sub.3 as its main component and a PbO--V.sub.2 O5--B.sub.2 O.sub.3 --SiO.sub.2 glass as an additive. For the same purpose, Japanese Unexamined Patent Publication No. 9-71462 has disclosed another dielectric ceramic composition containing BaO--TiO.sub.2 --Nd.sub.2 O.sub.3 --Sm.sub.2 O.sub.3 as its main component and also containing an additive which is a PbO--ZnO--B.sub.2 O.sub.3 glass having a softening point of 500.degree. C. or lower.

Since it is desired to let the dielectric ceramic compositions disclosed in Japanese Unexamined Patent Publication No. 8-239262 and Japanese Unexamined Patent Publication No. 9-71462 be sintered at a relatively low temperature during their manufacturing processes, each of the dielectric ceramic composition is formed by incorporating a glass which contains a Pb oxide component. Since the Pb oxide component has a high volatility during the process of manufacturing the glass and in a process of sintering the ceramic, the Pb oxide content will be different from lot to lot or even different in different portions of the same lot. As a result, there has been a problem that the properties of thus obtained ceramic are not stable.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved temperature compensating dielectric ceramic composition, and laminated ceramic parts such as a laminated ceramic condenser and a laminated LC filter, each of which is formed by using a temperature compensating dielectric ceramic composition having a high relative dielectric constant and a high Q value, and which can be sintered at a relatively low temperature during their manufacturing processes, without causing any undesired variations in ceramic properties during the sintering treatment.

In order to achieve the above object, a dielectric ceramic composition of the present invention comprises 100 parts by weight of a main component represented by a formula xBaO-yTiO.sub.2 -zRe.sub.2 O.sub.3 (wherein x+y+z=100 and Re is at least one rare earth element), having the mole composition ratio of BaO, TiO.sub.2 and Re.sub.2 O.sub.3 shown in a ternary composition diagram of FIG. 1, which is indicated by an area surrounded by point A (39.5. 59.5, 1), point B (1, 59.5, 39.5), point C (1, 85, 14) and point D (14, 85, 1); about 25 parts by weight or less of a first sub-component which is a B.sub.2 O.sub.3 --SiO.sub.2 glass not containing Pb oxide; a second sub-component which is at least one substance selected from V oxide and W oxide, the content of V oxide in the form of V.sub.2 O.sub.5 being about 10 parts by weight or less and the content of W oxide in the form of WO.sub.3 being about 20 parts by weight or less.

Further, another dielectric ceramic composition of the present invention comprises 100 parts by weight of a main component represented by a formula x(Ba.sub..alpha. Ca.sub..beta. Sr.sub..gamma.)O-y{(TiO.sub.2).sub.1-m (ZrO.sub.2).sub.m }-zRe.sub.2 O.sub.3 (wherein x+y+z=100, .alpha.+.beta.+.gamma.=1, 0.ltoreq..beta.+.gamma.<0.8, 0.ltoreq.m<0.15, but not including the case where .beta.+.gamma.=0 and m=0; Re is at least one rare earth element) having a mole composition ratio of ((Ba.sub..alpha. Ca.sub..beta. Sr.sub..gamma.)O, (TiO.sub.2).sub.1-m (ZrO.sub.2).sub.m and Re.sub.2 O.sub.3 shown in a ternary composition diagram of FIG. 2, which is indicated by an area surrounded by point A (39.5. 59.5, 1), point B (1, 59.5, 39.5), point C (1, 85, 14) and point D (14, 85, 1); about 25 parts by weight or less of a first sub-component which is a B.sub.2 O.sub.3 --SiO.sub.2 glass not containing Pb oxide; a second sub-component which is at least one substance selected from V oxide and W oxide, the content of V oxide in the form of V.sub.2 O.sub.5 being about 10 parts by weight or less and the content of W oxide in the form of WO.sub.3 being about 20 parts by weight or less.

Moreover, the dielectric ceramic composition of the present invention, apart from the above first and second sub-components, can further contain a third sub-component that is Cu oxide which in the form of CuO is in an amount of about 10 parts by weight or less with respect to 100 parts by weight of the main component.

In addition, the dielectric ceramic composition of the present invention, apart from the above first and second sub-components, or apart from the above first and second and third sub-components, can further contain a fourth sub-component that is Mn oxide which in the form of MnO is in an amount of about 20 parts by weight or less with respect to 100 parts by weight of the main component.

The laminated ceramic parts of the present invention can include a plurality of dielectric ceramic layers, internal electrodes formed between the dielectric ceramic layers, and external electrodes electrically connected with said internal electrodes, characterized in that said dielectric ceramic layers are formed by a dielectric ceramic composition recited above, said internal electrodes are formed by Cu or Ag serving as their main components.

The rare earth elements discussed in the present invention are La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a ternary composition diagram (BaO, TiO.sub.2, Re.sub.2 O.sub.3) indicating a preferred range for a main component contained in the composition of the present invention.

FIG. 2 is a ternary composition diagram {(Ba.sub..alpha. Ca.sub..beta. Sr.sub..gamma.)O, (TiO.sub.2).sub.1-m (ZrO.sub.2).sub.m, Re.sub.2 O.sub.3 } indicating a preferred range for a main component contained in the composition of the present invention.

FIG. 3 is a cross sectional view schematically indicating a laminated ceramic condenser made according to one embodiment of the present invention.

FIG. 4 is a plane view schematically indicating a dielectric ceramic layer carrying an internal electrode, which is a part of the laminated ceramic condenser of FIG. 3.

FIG. 5 is an exploded perspective view schematically indicating several ceramic layers forming a laminated structure, which is a part of the laminated ceramic condenser of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

At first, a description will be made to explain in detail a basic construction of a laminated ceramic condenser made according to a first embodiment of the present invention, with reference to the accompanying drawings. FIG. 3 is a cross sectional view schematically indicating one example of a laminated ceramic condenser of the present invention. FIG. 4 is a plane view schematically indicating a dielectric ceramic layer having an internal electrode, which is one portion of the laminated ceramic condenser of FIG. 3. FIG. 5 is an exploded perspective view schematically indicating laminated ceramic layers which are used to form the laminated ceramic condenser of FIG. 3.

The laminated ceramic condenser 1 made according to the present embodiment, as shown in FIG. 3, is comprised of a parallelepiped ceramic dielectric body 3 obtained by laminating a plurality of dielectric ceramic layers 2a, 2b with several internal electrodes 4 formed therebetween. On either end face of the ceramic laminated body 3, there is formed an external electrode 5 which is provided in a manner such that it is electrically connected to some specific internal electrodes. Further, if necessary, there are also formed a first plating layer 6 and a second plating layer 7 on either external electrode 5.

A method of manufacturing the above laminated ceramic condenser 1 will be described below.

At first, amounts of the raw material powders forming the dielectric ceramic layers 2a and 2b are prepared by weighing. Namely, the raw material powders are prepared which can be used to form the dielectric ceramic composition, such raw material powders containing a main component which is BaO--TiO.sub.2 --Re.sub.2 O.sub.3 (however, it also includes the case where Ba has been replaced by Ca or Sr and the case where TiO.sub.2 has been replaced by ZrO.sub.2), a first sub-component which is a B.sub.2 O.sub.3 --SiO.sub.2 glass (not containing Pb oxide), and a second sub-component which is at least one substance selected from V oxide and W oxide. Preferably, it is also desired to prepare raw material powders for forming the dielectric ceramic composition further containing a third sub-component that is Cu oxide or a fourth sub-component that is Mn oxide.

Next, an organic binder is added to the above raw material powders so as to form a slurry which is in turn formed into a sheet, thereby obtaining a green sheet useful for forming the dielectric ceramic layers 2a and 2b. After that, as shown in FIG. 4, an internal electrode 4 containing Cu or Ag as its main component is formed on one surface of a green sheet which will later be formed into the dielectric ceramic layer 2b. As a method for forming the internal electrode 4, it is also allowed to employ other methods such as screen printing, vapor deposition or plating.

Subsequently, as shown in FIG. 5, a plurality of green sheets for forming a dielectric ceramic layer 2b and each having an internal electrode 4 formed thereon, are arranged to be laminated in a manner shown in the drawing. Then, these green sheets are disposed so as to be pressed between two other green sheets which will later be formed into the dielectric layers 2a each of which does not carry an internal electrode, thereby obtaining a green she