Dielectric ceramic composition and laminated ceramic capacitor using the same

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a dielectric ceramic composition and a laminated ceramic capacitor using the same, especially to a ceramic capacitor having inner electrodes made of Ni.

2. Description of the Related Art

Ceramic layers and inner electrode metal layers are alternately stacked in the laminated ceramic capacitor. A cheap base metal such as Ni has been recently used for the inner electrodes in place of expensive noble metals such as Ag and Pd for reducing the production cost. When Ni is used for the electrodes, the capacitor should be fired in a reducing atmosphere where Ni is not oxidized. However, ceramics comprising barium titanate as a principal component may be endowed with semiconductive properties when the ceramics are fired in a reducing atmosphere. Accordingly, as disclosed for example in Japanese Examined Patent Publication No. 57-42588, a dielectric material in which the ratio between the barium site and titanium site in the barium titanate solid solution is adjusted to be larger than the stoichiometric ratio has been developed. This allows the laminated ceramic capacitor using Ni as electrodes to be practically used, thereby expanding its production scale.

Since electronic parts have been rapidly miniaturized with the recent advance of electronics, small size ceramic capacitors with large capacitance as well as temperature stability of electrostatic capacitance are required. The ceramic capacitors having the Ni electrodes are also under the same circumstances.

For complying with the requirements of large capacitance and small size, the dielectric ceramics should be made to be thinner and multi-layered. However, much higher voltage is impressed on the dielectric material when the dielectric ceramic layer is thinned, often causing troubles such as decrease of dielectric constant, increase of temperature dependency of the electrostatic capacitance and deteriorated stability of other characteristics when conventional dielectric materials are used. Especially, when the thickness of the dielectric layer is reduced to 5 .mu.m or less, 10 or less ceramic particles are contained between the inner electrodes, making it difficult to assure a stable quality.

Making the dielectric layer thin is accompanied by other problems. Solder plating layers as external electrodes are usually formed on the baked electrodes of a conductive metal powder in order to comply with automatic packaging of the laminated ceramic capacitor. Therefore, the plating layer is generally formed by electroplating. Oxides containing boron or a glass is added, on the other hand, into some dielectric ceramics as a sintering aid. However, the dielectric ceramic using these additives has so poor resistance against plating that characteristics of the laminated ceramic capacitor may be deteriorated by dipping it into a plating solution. It has been a problem that reliability is markedly decreased in the ceramic capacitor having thin dielectric ceramic layers.

SUMMARY OF THE INVENTION

Accordingly, the object of the present invention is to provide a laminated ceramic capacitor with high reliability and large capacitance especially using Ni for inner electrodes, wherein dielectric constant is not decreased exhibiting a stable electrostatic capacitance even when the dielectric ceramic layers are thinned, and temperature characteristics of the electrostatic capacitance satisfy the B-grade characteristics prescribed in the JIS standard and the X7R-grade characteristics prescribed in the EIA standard.

The present invention also provides a highly reliable laminated ceramic capacitor with large capacitance made of thin dielectric ceramic layers having an excellent plating solution resistance.

In one aspect, the present invention provides a laminated ceramic capacitor provided with a plurality of dielectric ceramic layers, inner electrodes formed between the dielectric ceramic layers and external electrodes being in electrical continuity with the inner electrodes, the dielectric ceramic layer being represented by the following formula:

(Ba.sub.1-x Ca.sub.x O).sub.m TiO.sub.2 +.alpha.Re.sub.2 O.sub.3 +.beta.MgO+.gamma.MnO

(Re.sub.2 O.sub.3 is at least one or more of the compounds selected from Y.sub.2 O.sub.3, Gd.sub.2 O.sub.3, Tb.sub.2 O.sub.3, Dy.sub.2 O.sub.3, Ho.sub.2 O.sub.3, Er.sub.2 O.sub.3 and Yb.sub.2 O.sub.3, .alpha.,.beta. .gamma., m and x representing molar ratio in the range of 0.001.ltoreq..alpha..ltoreq.0.10, 0.001.ltoreq..beta..ltoreq.0.12, 0.001<.gamma..ltoreq.0.12, 1.000<m .ltoreq.1.035 and 0.005<x.ltoreq.0.22), and containing about 0.2 to 5.0 parts by weight of either a first sub-component or a second sub-component relative to 100 parts by weight of a principal component containing about 0.02% by weight or less of alkali-metal oxides in (Ba.sub.1-x Ca.sub.x O).sub.m TiO.sub.2 as a starting material to be used for the dielectric ceramic layer, wherein the first sub-component is a Li.sub.2 O--(Si,Ti)O.sub.2 --MO based oxide (MO is at least one of the compound selected from Al.sub.2 O.sub.3 and ZrO.sub.2) and the second sub-component is a SiO.sub.2 --TiO.sub.2 --XO based oxide (XO is at least one of the compound selected from BaO, CaO, SrO, MgO, ZnO and MnO). The inner electrodes are preferably composed of nickel or a nickel alloy.

The material (Ba.sub.1-x Ca.sub.x O).sub.m TiO.sub.2 to be used for the dielectric ceramic layer preferably has a mean particle size of about 0.1 to 0.7 .mu.m.

The first sub-component represented by xLiO.sub.2 --y(Si.sub.w Ti.sub.1-w)Q.sub.2 --zMO (x, y and z are represented by molar percentage (mol %) and w is in the range of 0.30.ltoreq.w.ltoreq.1.0) may be within the area surrounded by the straight lines connecting between the succeeding two points represented by A (x=20, y=80, z=0), B (x=10, y=80, z=10), C (x=10, y=70, z=20), D (x=35, y=45, z=20), E (x=45, y=45, z=10) and F (x=45, y=55, z=0) or on the lines in a ternary composition diagram having apexes represented by each component LiO.sub.2, (Si.sub.w Ti.sub.1-w)O.sub.2 and MO provided that when the component is on the line A-F, w is in the range of 0.3.ltoreq.w.ltoreq.1.0.

The second sub-component represented by xSiO.sub.2 --yTiO.sub.2 --zXO (x, y and z are represented by mol %) may be within the area surrounded by the straight lines connecting between the succeeding two points represented by A (x=85, y=1, z=14), B (x=35, y=51, z=14), C (x=30, y=20, z=50) and D (x=39, y=1, z=60) or on the lines in a ternary composition diagram having apexes represented by each component SiO.sub.2, TiO.sub.2 and XO.

At least one of the compounds Al.sub.2 O.sub.3 and ZrO.sub.2 are contained with a combined amount of about 15 parts by weight (ZrO.sub.2 is about 5 parts by weight or less) in the second sub-component relative to 100 parts by weight of the SiO.sub.2 --TiO.sub.2 --XO based oxide.

The external electrodes are composed of sintered layers of a conductive metal powder or a conductive metal powder supplemented with a glass frit.

Alternately, the external electrodes are composed of sintered layers of a conductive metal powder or a conductive metal powder supplemented with a glass frit, and plating layers formed thereon.

It is preferable to use the ceramic having the composition to be described hereinafter in order to improve the plating resistance. The dielectric ceramic layer in the laminated ceramic capacitor is represented by the following formula:

(Ba.sub.1-x Ca.sub.x O).sub.m TiO.sub.2 +.alpha.Re.sub.2 O.sub.3 +.beta.MgO+.gamma.MnO

(Re.sub.2 O.sub.3 is at least one or more of the compounds selected from Y.sub.2 O.sub.3, Gd.sub.2 O.sub.3, Tb.sub.2 O.sub.3, Dy.sub.2 O.sub.3, Ho.sub.2 O.sub.3, Er.sub.2 O.sub.3 and Yb.sub.2 O.sub.3, .alpha., .beta. .gamma., m and x representing molar ratio in the range of 0.001.alpha..ltoreq.0.10, 0.001.ltoreq..beta.0.12, 0.001<.gamma..ltoreq.0.12, 1.000<m.ltoreq.1.035 and 0.005<x.ltoreq.0.22), and contains about 0.2 to 5.0 parts by weight of the compound selected from either a first sub-component, a second sub-component or a third sub-component relative to 100 parts by weight of a principal component containing about 0.02% by weight or less of alkali-metal oxides in (Ba.sub.1-x Ca.sub.x O).sub.m TiO.sub.2 as a starting material to be used for the dielectric ceramic layers, wherein the first sub-component is a Li.sub.2 O--B.sub.2 O.sub.3 --(Si, Ti)O.sub.2 based oxide, the second sub-component is a Al.sub.2 O.sub.3 --MO--B.sub.2 O.sub.3 based oxide (MO is at least one of the compound selected from BaO, CaO, SrO, MgO, ZnO and MnO) and the third sub-component is SiO.sub.2.

The first sub-component represented by xLiO.sub.2 --YB.sub.2 O.sub.3 --Z(Si.sub.w Ti.sub.1-w)O.sub.2 (x, y and z are represented by mol % and w is in the range of 0.30.ltoreq.w.ltoreq.1.0) is preferably within the area surrounded by the straight lines connecting between the succeeding two points represented by A (x=0, y=20, z=80), B (x=19, y=1, z=80), C (x=49, y=1, z=50), D (x=45, y=50, z=5), E (x=20, y=75, z=5) and F (x=0, y=80, z=20) or on the lines in a ternary composition diagram having apexes represented by each component LiO.sub.2, B.sub.2 O.sub.3 and (Si.sub.w Ti.sub.1-w)O.sub.2.

At least one of the compounds Al.sub.2 O.sub.3 and ZrO.sub.2 are contained in a combined amount of about 20 parts by weight or less (ZrO.sub.2 is about 10 parts by weight or less) in the first sub-component relative to 100 parts by weight of the Li.sub.2 O--B.sub.2 O.sub.3 --(Si, Ti)O.sub.2 based oxide.

The second sub-component represented by xAl.sub.2 O.sub.3 --yMO--zB.sub.2 O.sub.3 (x, y and z are represented by mol %) is preferably within the area surrounded by the straight lines connecting between the succeeding two points represented by A (x=1, y=14, z=85), B (x=20, y=10, z=70), C (x=30, y=20, z=50), D (x=40, y=50, z=10), E (x=20, y=70, z=10) and F (x=1, y=39, z=60) or on the lines in a ternary composition diagram having apexes represented by each component Al.sub.2 O.sub.3, yMO and zB.sub.2 O.sub.3.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section showing one example of the laminated ceramic capacitor according to the present invention.

FIG. 2 is a plane view showing the dielectric ceramic layer part having the inner electrodes in the laminated ceramic capacitor shown in FIG. 1.

FIG. 3 is a disassembled perspective view showing the laminated ceramic part in the laminated ceramic capacitor shown in FIG. 1.

FIG. 4 is a ternary composition diagram of the LiO.sub.2 --(Si.sub.w Ti.sub.w-w)O.sub.2 --MO based oxide.

FIG. 5 is a ternary composition diagram of the SiO.sub.2 --TiO.sub.2 --XO based oxide.

FIG. 6 is a ternary composition diagram of the Li.sub.2 O--B.sub.2 O.sub.3 --(Si.sub.w Ti.sub.1-w)O.sub.2 based oxide.

FIG. 7 is a ternary composition diagram of the Al.sub.2 O.sub.3 --MO--B.sub.2 O.sub.3 based oxide.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The laminated ceramic capacitor according to the present invention will now be explained in more detail with reference to the accompanying drawings.

FIG. 1 is a cross section showing one example of the laminated ceramic capacitor according to the present invention, FIG. 2 is a plane view showing the dielectric ceramic layer part having the inner electrodes in the laminated ceramic capacitor shown in FIG. 1 and FIG. 3 is a disassembled perspective view showing the laminated ceramic part in the laminated ceramic capacitor shown in FIG. 1. In the laminated ceramic capacitor 1 according to the present invention as shown in FIG. 1, outer electrodes 5, and first plating layers 6 and second plating layers 7 if necessary, are formed on both ends of a ceramic laminated body 3 obtained by laminating a plurality of dielectric ceramic layers 2a and 2b via inner electrodes 4.

The dielectric ceramic layers 2a and 2b are composed of a dielectric ceramic composition having as principal components barium calcium titanate (Ba.sub.1-x Ca.sub.x O).sub.m TiO.sub.2, at least one compound selected from Y.sub.2 O.sub.3, Gd.sub.2 O.sub.3, Tb.sub.2 O.sub.3, Dy.sub.2 O.sub.3, Ho.sub.2 O.sub.3, Er.sub.2 O.sub.3 and Yb.sub.2 O.sub.3, MgO and MnO, and containing as sub-components either a Li.sub.2 O--(Si, Ti)O.sub.2 --MnO based oxide (MO is at least one of the compounds selected from Al.sub.2 O.sub.3 and ZrO.sub.2) or a SiO.sub.2 --TiO.sub.2 --XO based oxide (XO is at least one of the compounds selected from BaO, CaO, SrO, MgO, ZnO and Mno). The composition described above allows a laminated ceramic capacitor with high reliability and excellent insulating strength to be obtained, wherein the ceramic capacitor can be fired without endowing it with semiconductive properties even by firing in a reducing atmosphere, the temperature characteristics of the electrostatic capacitance satisfy the B-grade characteristics prescribed in the JIS standard and the X7R-grade characteristics prescribed in the EIA standard and the ceramic capacitor has a high insulation resistance at room temperature and at high temperatures.

Also, a highly reliable laminated ceramic capacitor, whose dielectric constant is less affected by variation of electric field even when the dielectric ceramic layers are thinned and magnetic field strength is increased, can be obtained by using a barium calcium titanate material with a mean particle size of about 0.1 to 0.7 .mu.m. The dielectric ceramic assumes a core-shell structure in which Re components (Re is at least one or more of the elements selected from Y, Gd, Tb, Dy, Ho, Er and Yb) are distributed in the vicinity of and at grain boundaries by diffusion during firing.

A highly reliable dielectric material can be also obtained by using a barium calcium titanate containing about 0.02% by weight or less of alkali metal oxides such as Na.sub.2 O and K.sub.2 O.

The ratio (n) of (barium+calcium)/titanium in the barium calcium titanate material is not specifically limited. However, the ratio (n) in the range from about 0.990 to 1.035 is desirable when stability for producing powder materials is taken into consideration.

Li.sub.2 O--(Si, Ti)O.sub.2 --MO based oxides contained in the principal components described above serve for firing the dielectric ceramics at a relatively low temperature of 1250.degree. C., improving high temperatures load characteristics. SiO.sub.2 --TiO.sub.2 --XO based oxides included in the principal components also allow the sintering property to be excellent along with improving the voltage load characteristics at a high temperature and humidity. Further, a higher insulation resistance can be obtained by allowing Al.sub.2 O.sub.3 and ZrO.sub.2 to be contained in the SiO.sub.2 --TiO.sub.2 --XO based oxides.

The inner electrode 4 is composed of base metals such as nickel or a nickel alloy.

The outer electrode 5 is composed of a sintered layer of various conductive metals such as Ag, Pd, Ag--Pd, Cu or a Cu alloy, or a sintered layer prepared by blending the foregoing conductive metal powder with various glass fits such as B.sub.2 O.sub.3 --Li.sub.2 O--SiO.sub.2 --BaO based, B.sub.2 O.sub.3 --SiO.sub.2 --BaO based, Li.sub.2 O--SiO.sub.2 --BaO based or B.sub.2 O.sub.3 --SiO.sub.2 --ZnO based glass frit. It is possible to form a plating layer on this sintered layer. Either a first plating layer 6 comprising Ni, Cu or a Ni--Cu alloy may be merely formed or a second plating layer 7 comprising tin or a solder may be formed on the first plating layer.

The method for producing the laminated ceramic capacitor according to the present invention will be described hereinafter in the order of its production steps with reference to FIGS. 1 to 3.

Powder materials produced by a solid phase method for allowing oxides and carbonates to react at a high temperature or a powder material produced by a wet synthesis method such as a hydrothermal synthesis method or alkoxide method are prepared as starting materials of the dielectric ceramics. A solution of an alkoxide or an organometallic compound may be used for the additives other than oxides and carbonates.

After weighing the prepared materials in a prescribed composition ratio with mixing, the mixed powder is turned into a slurry by adding an organic binder to obtain a green sheet (the dielectric ceramic layers 2a and 2b) by molding the slurry into a sheet. The inner electrodes 4 comprising nickel or a nickel alloy are then formed on one face of the green sheet (the dielectric ceramic layers 2b). Any method including screen printing, vacuum deposition or plating may be used for forming the inner electrodes 4.

Then, a required number of the green sheets (the dielectric ceramic layers 2b) having the inner electrodes 4 are laminated, which are inserted between the green sheets having no inner electrodes (the dielectric ceramic layers 2a) to form a laminated body after pressing. A ceramic laminated body 3 is obtained by firing the laminated body at a given temperature in a reducing atmosphere.

A pair of the outer electrodes 5 are formed on both side ends of the ceramic laminate body 3 so as to be in electrical continuity with the inner electrodes 4. While the outer electrodes 5 are usually formed by coating the metal powder paste on the ceramic laminated body 3 obtained by firing and baking the paste, the outer electrode may be formed simultaneously with forming the ceramic laminated body 3 by coating the paste prior to firing.

Finally, the first plating layer 6 and the second plating layer 7 are formed, if necessary, on the outer electrodes 5, thereby completing the laminated ceramic capacitor 1.

EXAMPLES

Example 1

Starting materials TiO.sub.2, BaCO.sub.3 and CaCO.sub.3 are at first prepared. After mixing and crushing the materials, the mixture is heated at 1000.degree. C. or more to synthesize nine kinds of barium calcium titanate shown in TABLE 1. The mean particle size was determined by observing the particles of the material under a scanning electron microscope.

TABLE 1 Kind of Content of Alkali Barium Metal Oxide Mean Calcium (Ba.sub.1-x Ca.sub.x O).sub.n TiO.sub.2 (Ba + Ca)/Ti Impurities Particle Titanate x n (% by weight) Size (.mu.m) A 0.003 1.000 0.003 0.50 B 0.100 1.000 0.010 0.50 C 0.200 0.998 0.012 0.50 D 0.250 0.998 0.015 0.50 E 0.100 1.000 0.062 0.50 F 0.080 1.005 0.003 0.15 G 0.100 1.008 0.020 0.25 H 0.100 1.000 0.010 0.75 I 0.100 1.000 0.010 0.08

Oxides, carbonates and hydroxides of respective components of the first sub-component were weighed so as to be a composition (molar) ratio of 0.25Li.sub.2 O-0.65(0.30TiO.sub.2. 0.70SiO.sub.2)- 0.10Al.sub.2 O.sub.3 and the mixture was crushed to obtain a powder. Likewise, oxides, carbonates and hydroxides of respective components of the second sub-component were weighed so as to be a composition ratio of 0.66Si.sub.2 O-0.17TiO.sub.2 -0.15BaO-0.02MnO (molar ratio) and the mixture was crushed to obtain a powder. Then, after heating the powders of the first and second sub-components to 1500.degree. C. in different crucibles, respectively, they were quenched and crushed to obtain respective oxide powders with a mean particle size of 1 .mu.m or less.

In the next step, BaCO.sub.3 or TiO.sub.2 for adjusting the molar ratio m of (Ba, Ca)/Ti in the barium calcium titanate, and Y.sub.2 O.sub.3, Gd.sub.2 O.sub.3, Tb.sub.2 O.sub.3, Dy.sub.2 O.sub.3, Ho.sub.2 O.sub.3, Er.sub.2 O.sub.3, Yb.sub.2 O.sub.3, MgO and MnO with purity of 99% or more were prepared. These powder materials and the foregoing oxide powders for the first and second sub-components were weighed to be the compositions shown in TABLE 2. The amount of addition of the first and second sub-components are given in parts by weight relative to 100 parts by weight of the principal component, i.e., (Ba.sub.1-x Ca.sub.x O).sub.m TiO.sub.2 +.alpha.Re.sub.2 O.sub.3 +.beta.MgO+.gamma.MnO. A polyvinyl butylal based binder and an organic solvent such as ethanol were added to the weighed materials and the mixture was wet-milled with a ball-mill to prepare a ceramic slurry. This ceramic slurry was formed into a sheet by a doctor blade method, obtaining a rectangular green sheet with a thickness of 4.5 .mu.m. Then, a conductive paste mainly containing Ni was printed on the ceramic green sheet to form conductive paste layers constituting the inner electrodes.

TABLE 2 The The (Ba1 - xCaxO)m.TiO2 + .beta.MgO + .gamma.MnO First Second Kind of Sub-Com- Sub-Com- Sam- Barium ponent ponent ple Calcium .alpha. (parts by (parts by No. Titanate x m Y2O3 Gd2O3 Tb2O3 Dy2O3 Ho2O3 Er2O3 Yb2O3 .beta. .gamma. weight) weight) *1 A 0.003 1.01 0 0 0 0.02 0 0 0 0.02 0.005 1 0 *2 D 0.250 1.01 0 0 0 0.02 0 0 0 0.02 0.005 1 0 *3 B 0.100 1.01 0 0 0 0.0005 0 0 0 0.02 0.005 1 0 *4 B 0.100 1.01 0 0 0 0.11 0 0 0 0.02 0.005 1 0 *5 B 0.100 1.01 0 0 0 0.02 0 0 0 0.0008 0.005 1 0 *6 B 0.100 1.01 0 0 0 0.02 0 0 0 0.13 0.005 1 0 *7 B 0.100 1.01 0 0 0 0.02 0 0 0 0.02 0.0008 1 0 *8 B 0.100 1.01 0 0 0 0.02 0 0 0 0.02 0.13 1 0 *9 B 0.100 0.995 0 0 0 0.02 0 0 0 0.02 0.005 1 0 *10 B 0.100 1 0 0 0 0.02 0 0 0 0.02 0.005 1 0 *11 B 0.100 1.036 0 0 0 0.02 0 0 0 0.02 0.005 1 0 *12 B 0.100 1.01 0 0 0 0.02 0 0 0 0.02 0.005 0 0 *13 B 0.100 1.01 0 0 0 0.02 0 0 0 0.02 0.1 0 0 *14 B 0.100 1.01 0 0 0 0.02 0 0 0 0.02 0.005 5.5 0 *15 B 0.100 1.01 0 0 0 0.02 0 0 0 0.02 0.005 0 5.5 *16 E 0.100 1.01 0 0 0 0.02 0 0 0 0.02 0.005 i 0 17 H 0.100 1.01 0 0 0 0.02 0 0 0 0.02 0.005 1 0 18 I 0.100 1.01 0 0 0 0.02 0 0 0 0.02 0.005 1 0 19 G 0.100 1.025 0.025 0 0 0 0 0 0 0.02 0.005 0 1 20 G 0.100 1.02 0 0.08 0 0 0 0 0 0.05 0.008 4 0 21 G 0.100 1.015 0 0 0.05 0 0 0 0 0.05 0.005 3 0 22 B 0.100 1.01 0 0 0 0 0.02 0 0.02 0.05 2 0 23 B 0.100 1.01 0 0 0 0 0 0.02 0 0.02 0.05 0 1 24 G 0.200 1.005 0 0 0 0 0 0 0.03 0.02 0.05 0 1 25 C 0.200 1.005 0.005 0 0 0.02 0 0 0 0.02 0.005 0 1 26 F 0.080 1.015 0.005 0.015 0 0 0 0 0 0.02 0.005 2 0 27 F 0.080 1.015 0 0 0 0.02 0 0 0 0.02 0.005 0 2 *The samples marked (*) are out of the range of the present invention.

Next, a plurality of ceramic green sheets on which the conductive paste layers had been formed were laminated to obtain a laminated body so that the sides where the conductive paste layers are exposed alternately come to the opposite ends. The laminated body was heated at a temperature of 350.degree. C. in a N.sub.2 atmosphere. After driving out the binder, the laminated body was fired in a reducing atmosphere comprising a H.sub.2 --N.sub.2 --H.sub.2 O gas with an oxygen partial pressure of 10.sup.-9 to 10.sup.-12 MPa to obtain a ceramic sintered body.

After firing, an Ag paste containing a B.sub.2 O.sub.3 --Li.sub.2 --SiO.sub.2 --BaO based glass frit was coated on both side faces of the ceramic sintered body, which was baked at a temperature of 600.degree. C. in the N.sub.2 atmosphere to form the outer electrodes electrically connected to the inner electrodes.

The laminated ceramic capacitor thus obtained had an overall dimension with a width of 5.0 mm, a length of 5.7 mm and a thickness of 2.4 mm with a thickness of the dielectric ceramic layers inserted between the inner electrodes of 3 .mu.m. The total number of the effective dielectric ceramic layers was five with a confronting electrode area per layer of 16.3.times.10.sup.-6 m.sup.2.

Electric characteristics of these laminated ceramic capacitors were then determined. Electrostatic capacitances and dielectric losses (tan .delta.) were measured per JIS C5102 standard using an automatic bridge type measuring apparatus and dielectric constant was calculated from the electrostatic capacitance obtained. Insulation resistance was also measured using an insulation resistance meter by impressing a direct-current voltage of 10 V for 2 minutes to calculate resistivity (.rho.).

DV vias characteristics were also measured. The electrostatic capacitance was determined while impressing a direct-current voltage of 15 V (5 kV/mm) and the rate of change of the electrostatic capacitance (.DELTA.C %) was determined relative to the electrostatic capacitance measured without impressing a direct-current voltage.

The rate of temperature dependent change of the electrostatic capacitance was also measured. The maximum value of the rate of change in the temperature range from -25.degree. C. to 85.degree. C. relative to the capacitance at 20.degree. C. (.DELTA.C/C20) and the maximum value of the rate of change in the temperature range from -55.degree. C. to 125.degree. C. relative to the capacitance at 25.degree. C. (.DELTA.C/C25) were determined with respect to the rate of change of the capacitance.

A high temperature load test was carried out by measuring the time dependent changes of the insulation resistance when a direct-current voltage of 30 V was impressed at 150.degree. C. Lifetime of each sample was defined to be the time when the insulation resistance of each sample had decreased to 10.sup.5 .OMEGA. or less, and a mean lifetime was determined using a plurality of the samples.

The dielectric breakdown voltage was measured by impressing DC voltages with a voltage increasing rate of 100 V/sec. The results are summarized in TABLE 3.

TABLE 3 Rate of Change Rate of Temperature Depen- Dielectric of Capacitance dent Change of Capacitance Dielectric Burning Loss .DELTA.C% .DELTA.C/C20% .DELTA.C/C25% Resistivity Breakdown Voltage Mean Sample Temp. Dielectric tan .delta. DC -25.about.+85.degree. C. -55.about.+125.degree. C. Log .rho. DC Lifetime No. (.degree. C.) Constant (%) 5Kv/mm (%) (%) (.OMEGA..cm) (kV/mm) (h) *1 1300 3360 4.5 -65 -9.7 -15.6 13.2 14 3 *2 1250 1130 9.3 -35 -4.5 -6.5 13.1 15 23 *3 1250 2430 4.6 -55 -1.5 -10.6 13.2 14 2 *4 1250 1220 3.1 -37 -18.1 -23.3 13.5 15 15 *5 1250 2570 3.6 -63 -15.6 -24.7 12.9 12 65 *6 1350 1760 4.4 -45 -7.8 -14.6 13.1 14 2 *7 1250 1950 4.7 -57 -9.6 -15.4 11.8 14 17 *8 1250 1730 3.8 -56 -13.6 -19.7 11.2 14 8 *9 1250 2100 5.6 -60 -12.3 -18.6 11.2 8 - *10 1250 2060 5.3 -62 -12.2 -17.5 11.6 9 - *11 1300 1950 4.4 -50 -8.6 -14.4 12.3 9 1 *12 1350 1530 5.1 -45 -8.8 -13.7 11.4 10 - *13 1350 1470 5.3 -47 -8.9 -14.2 11.5 9 - *14 1200 1680 3.2 -48 -14.5 -30.6 13.1 14 5 *15 1200 1740 3.4 -42 -13.3 -26.8 13.1 14 3 *16 1250 1750 3.7 -48 -10.5 -15.1 13.1 14 21 17 1250 2370 4.7 -51 -4.7 -6.7 13.1 13 52 18 1150 1040 2.5 -30 -8.4 -14.2 13.5 15 174 19 1175 1410 2.2 -35 -9.6 -14.4 13.2 14 85 20 1150 1260 2.3 -33 -8.8 -13.7 13.2 15 110 21 1175 1260 2.3 -36 -9.2 -14.6 13.2 14 105 22 1200 1900 2.1 -42 -8.6 -13.4 13.2 14 85 23 1250 2010 2.5 -44 -8.5 -13.8 13.2 15 80 24 1250 1430 1.8 -34 -7.8 -11.4 13.1 14 110 25 1250 1450 1.9 -31 -8.2 -11.1 13.2 15 120 26 1175 1260 1.7 -32 -9.5 -14.5 13.2 14 92 27 1175 1340 1.6 -33 -9.2 -13.5 13.2 14 95 *The samples marked by (*) are out of the range of th e present invention.

The cross section of the laminated ceramic capacitor obtained was polished and subjected to chemical etching. It was found from scanning electron microscopic observation of the grain size in the dielectric ceramics that the grain size was almost equal to the particle size of the barium calcium titanate starting material in the samples having the compositions within the range of the present invention.

As are evident from TABLE 1 to TABLE 3, the rate of temperature dependent change of the electrostatic capacitance satisfies the B-grade characteristic standard prescribed in the JIS standard in the temperature range from -25.degree. C. to +85.degree. C., along with satisfying the X7R-grade characteristic standard prescribed in the EIA standard in the temperature range from -55.degree. C. to +125.degree. C., in the laminated ceramic capacitor according to the present invention. In addition, the rate of change of the capacitance when a DC voltage of 5 kV/mm is impressed is as small as within 51%, the change of the electrostatic capacitance being also small when the capacitor is used has thin layers. Moreover, the mean lifetime in the high temperature load test is as long as 52 hours or more, enabling one to fire at a firing temperature of 1250.degree. C. or below.

The reason why the compositions are limited in the present invention will be described hereinafter.

In the composition represented by the following formula:

(Ba.sub.1-x Ca.sub.x O).sub.m TiO.sub.2 +.alpha.Re.sub.2 O.sub.3 +.beta.MgO+.gamma.MnO

(Re.sub.2 O.sub.3 represents at least one of the compounds selected from Y.sub.2 O.sub.3, Gd.sub.2 O.sub.3, Tb.sub.2 O3, Dy.sub.2 O.sub.3, Ho.sub.2 O.sub.3, Er.sub.2 O.sub.3 and Yb.sub.2 O.sub.3 and .alpha., .beta. and .gamma. represent molar ratios), a CaO content (x) of about 0.005 or less as in the sample No. 1 is not preferable since the rate of impressed voltage dependent change of the capacitance becomes large and the mean lifetime becomes extremely short. It is also not preferable that the CaO content (x) exceeds about 0.22 as in the sample No. 2 because the dielectric loss is increased. Accordingly, the preferable CaO content (x) is in the range of 0.005<x.ltoreq.0.22.

A Re.sub.2 O.sub.3 content (.alpha.) of less than about 0.001 as in the sample No. 3 is also not preferable because the mean lifetime becomes extremely short. It is also not preferable that the content of Re.sub.2 O.sub.3 (.alpha.) exceed about 0.10 since the temperature characteristics do not satisfy the B/X7R-grade characteristics while the mean lifetime is shortened. Accordingly, the preferable Re.sub.2 O.sub.3 content (.alpha.) is in the range of 0.001.ltoreq..alpha..ltoreq.0.10.

A MgO content (.beta.) of less than about 0.001 as in the sample No. 5 is also not preferable because the rate of impressed voltage dependent change of the capacitance becomes large while the temperature characteristics do not satisfy the B/X7R-grade characteristics. It is also not preferable that the amount of addition (.beta.) of MgO exceed about 0.12 as in the sample No. 6 since the sintering temperature becomes high to extremely shorten the mean lifetime. Accordingly, the preferable MgO content (.beta.) is in the range of 0.001.ltoreq..beta..ltoreq.0.12.

A MnO content (.gamma.) of less than about 0.001 as in the sample No. 7 is also not preferable because the capacitance is lowered while the mean lifetime is shortened. It is also not preferable that the MnO content (.gamma.) exceed about 0.12 as in the sample No. 8 since the temperature characteristics do not satisfy the B/X7R-grade characteristics, the resistivity becomes low and the mean lifetime is shortened. Accordingly, the preferable range of the MnO content (.gamma.) is 0.001<.gamma..ltoreq.0.12.

It is not preferable that the ratio (m) of (Ba, Ca)/Ti is less than about 1.000 as in the samples No. 9 and No. 10 because the temperature characteristics do not satisfy the B/X7R-grade characteristics, thereby lowering the resistivity besides immediately causing short circuit troubles when a voltage is impressed in the high temperature load test. It is also not preferable that the ratio (m) of (Ba, Ca)/Ti exceed about 1.035 as in the sample No. 11 because sintering is insufficient to extremely shorten the mean lifetime. Accordingly, the preferable ratio (m) of (Ba, Ca)/Ti is in the range of 1.000<m.ltoreq.1.035.

It is not preferable that the contents of the first and second sub-components are zero as in the samples No. 12 and No. 13 because the resistivity is lowered to immediately cause short circuit troubles when a voltage is impressed in the high temperature load test. It is also not preferable that the contents of the first and second sub-components exceed about 5.0 parts by weight as in the sample Nos. 14 and 15 because the second phase based on glass components is increased and the temperature characteristics do not satisfy the B/X7R-grade characteristics and the mean lifetime is extremely shortened. Accordingly