Dielectric ceramic composition and monolithic ceramic capacitor using same

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BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a dielectric ceramic composition and monolithic ceramic capacitor using the same.

2. Description of the Related Art

The conventional ceramic capacitor is usually produced by the following process.

First, a sheet of a dielectric material coated on its surface with an electrode material to serve as an inner electrode is prepared. A material essentially composed of BaTiO.sub.3 is used for the dielectric material. Then, the sheet of the dielectric material coated with this electrode material is laminated with heat-pressing to form a monolithic body followed by firing at 1250 to 1350.degree. C. in an environment to obtain a ceramic monolithic body having inner electrodes. A monolithic ceramic capacitor is obtained by glazing outer electrodes electrically connected to the inner electrodes.

Noble metals such as platinum, gold, palladium or silver have been conventionally used for the material of the inner electrode of this monolithic. ceramic capacitor. However, these electrode materials are expensive although having excellent characteristics, rendering the production cost high. Therefore, a monolithic capacitor using base metals such as Ni as the inner electrode is currently proposed to reduce the production cost, and its application in the market being steadily increasing.

In the trend to make electronic appliances compact, high performance and low price, strongly required is a monolithic capacitor of even lower price, improved in insulation durability, insulating property and reliability, and having a large capacitance. Although it is advantageous to use an inexpensive monolithic ceramic capacitor in which nickel is used for the inner electrode for reducing the price of the electronic appliances, there is the problem that the insulation resistance, insulation durability and reliability extremely deteriorate when the electronic appliances are used under a high electric field strength because conventional dielectric ceramic materials are designed on the premise that they are used under a low electric field strength. In other words, there has been no monolithic ceramic capacitor capable of use under a high electric field strength when using nickel for the inner electrode.

For example, while the dielectric materials disclosed in Japanese Examined Patent Publication No. 57-42588 and Japanese Unexamined Patent Publication No. 61-101459 display a large dielectric constant, the grain size of the dielectric ceramic is large, thereby exhibiting deficiencies such that the insulation durability of the monolithic ceramic capacitor becomes low when it is used under a high electric field strength or the mean life span under the high temperature load test is short.

In the dielectric material disclosed in Japanese Examined Patent Publication No. 61-14611, there was a deficiency that the dielectric constant, or the electrostatic capacitance, becomes extremely lowered when the capacitor is used under a high electric field strength, although its dielectric constant obtained under a low electric field strength is as high as 2000 to 2800. There is also the deficiency that the insulation resistance is low.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a dielectric ceramic composition capable of forming, for example, dielectric ceramic layers of a monolithic ceramic capacitor, wherein the insulation resistance represented by the product with the electrostatic capacitance (the product CR) is as high as about 4900 to 5000 .OMEGA..cndot.F or more at room temperature and about 200 .OMEGA..cndot.F or more at 150.degree. C., respectively, when the capacitor is used under a high electric field strength of, for example, as high as about 10 kV/mm, along with having a small voltage dependence of the insulation resistance, excellent stability of the electrostatic capacitance against DC vias voltage, being high in insulation durability while the temperature characteristics of the electrostatic capacitance satisfies both the B-level characteristic standard stipulated in the JIS Standard and X7R-level characteristic standard stipulated in the EIA standard and having excellent weather resistance performance as shown by a high temperature load test and high humidity load test. Another object of the present invention is to provide a monolithic ceramic capacitor whose inner electrode is constructed of Ni or Ni alloys along with using such dielectric ceramic composition as the dielectric ceramic layer.

In broad terns, provided is a monolithic ceramic capacitor employing a dielectric ceramic composition comprising barium titanate, barium zirconate, manganese oxide, and at least one of Sc.sub.2 O.sub.3. Y.sub.2 O.sub.3, Eu.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, Tm.sub.2 O.sub.3 and Yb.sub.2 O.sub.3, as a also Li.sub.2 O--(Si, Ti)O.sub.2 --MO or SiO.sub.2 --TiO.sub.2 --XO, and optionally MgO.

In a first preferred aspect, the present invention provides a dielectric ceramic composition comprising barium titanate containing about 0.02% by weight or less of alkali metal oxides, at least one of scandium oxide or yttrium oxide, at least one of compound europium oxide, gadolinium oxide, terbium oxide and dysprosium oxide, and barium zirconate and manganese oxide, and corresponding to the composition formula

(wherein M.sub.2 O.sub.3 represents at least one of Sc.sub.2 O.sub.3 or Y.sub.2 O.sub.3 and R.sub.2 O.sub.3 represents at least one of Eu.sub.2 O.sub.3, Gd.sub.2 O.sub.3, Tb.sub.2 O.sub.3 and Dy.sub.2 O.sub.3, .alpha., .beta., .gamma.and g represent mo range of 0.01.ltoreq..alpha.<0.04, 0.01.ltoreq..beta..ltoreq.0.04, 0.01.ltoreq..gamma..ltoreq.0.04, 0.01<g.ltoreq.0.12 and .alpha.+.beta..ltoreq.0.05 with 1.01<m.ltoreq.1.03),

along with containing about 1 to 2 parts by weight of either a first or second side component relative to 100 parts by weight of the essential component defined by said formula, wherein the first side component is an oxide represented by Li.sub.2 O--(Si, Ti)O.sub.2 --MO (wherein MO is at least one of Al.sub.2 O.sub.3 or ZrO.sub.2) and the second side component is an oxide represented by SiO.sub.2 --TiO.sub.2 --XO (wherein XO is at least one of BaO, CaO, SrO, MgO, ZnO and MnO).

In the dielectric ceramic composition described above, the essential component may further contain h moles of magnesium oxide, where

0.001<g.ltoreq.0.12, 0.001<h.ltoreq.0.12and g+h.ltoreq.0.13

In the dielectric ceramic composition according to another aspect of the present invention, the essential component may be represented by the following composition formula

(wherein M.sub.2 O.sub.3 represents at least one of either Sc.sub.2 O.sub.3 or Y.sub.2 O.sub.3, where .alpha., .gamma. and g representing mole ratio in the range of 0.001.ltoreq..alpha..ltoreq.0.06, 0.005.ltoreq..gamma.<0.06 and 0.001<g<0.13 with 1.000<m.ltoreq.1.035).

The essential component may further contain h moles of magnesium oxide, where 0.001<g.ltoreq.0.12, 0.001<h.ltoreq.0.12 and g+h.ltoreq.0.13.

According to a different aspect of the present invention, the essential component may be represented by the following composition formula

(wherein R.sub.2 O.sub.3 represents at least one of Eu.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, Tm.sub.2 O.sub.3 and Yb.sub.2 O.sub.3, where .alpha., .gamma. and g represent moles in the range of 0.001.ltoreq..alpha..ltoreq.0.06, 0.005.ltoreq..gamma..ltoreq.0.06 and 0.001<g.ltoreq.0.13 with 1.000<m.ltoreq.1.025).

The essential component may further contain h moles of magnesium oxide, where 0.001.ltoreq..gamma..ltoreq.0.06, 0.001<g.ltoreq.0.12, 0.001<h.ltoreq.0.12 and g+h.ltoreq.0.13.

In the dielectric ceramic compositions described above, it is preferable that the first side component, when its composition is represented by xLi.sub.2 O--y(SiN.sub.w,Ti.sub.1-w)O.sub.2 --zMO (wherein x, y and z represent mol % and w is in the range of 0.30.ltoreq.w.ltoreq.1.00), falls within or on the boundary lines of the area surrounded by straight lines connecting the points indicated by A (x=20, y=80, z=0), B (x =10, y=80, z=10), C (x=10, y=70, z=20), D (x=20), E (x=45, y=45, z=10) and F (x=45, y=55, z=0) provided that when the composition falls on the straight line of A-F, w is within the area of 0.3.ltoreq.w<1.0 on a three component diagram defined by the apexes corresponding to each component.

In the dielectric ceramic compositions described above, it is preferable that the second side component, when its composition is represented by xSiO2--yTiO.sub.2 --zXO (wherein x, y and z represent mol %), falls within or on the boundary lines of the area surrounded by straight lines connecting the points indicated 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) in the three component diagram defined by the apexes corresponding to each component.

The second side component contains in total about 15 parts by weight of at least one of Al.sub.2 O.sub.3 and ZrO.sub.2 (the content of ZrO.sub.2 is about 5 parts by weight or less) relative to 100 parts by weight of the oxide represented by SiO.sub.2 --TiO.sub.2 --XO.

The present invention according to a different aspect provides a monolithic ceramic capacitor provided with a plurality of dielectric ceramic layers, inner electrodes formed between the ceramic layers and outer electrodes electrically connected to the inner electrodes, wherein the dielectric ceramic layers are constructed by the dielectric ceramic composition described above and the inner electrodes are composed of nickel or a nickel alloy.

The outer electrode may be provided with a sintered layer of an electroconductive metal powder or an electroconductive metal powder supplemented with glass frits.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view showing the monolithic ceramic capacitor according to one embodiment of the present invention.

FIG. 2 is a plane view showing the dielectric ceramic layer portion having inner electrodes of the monolithic ceramic capacitor shown in FIG. 1.

FIG. 3 is a disassembled perspective view showing the ceramic monolithic portion of the monolithic ceramic capacitor shown in FIG. 1.

FIG. 4 is a three component phase diagram of Li.sub.2 O--(Si.sub.w, Ti.sub.1-w)O.sub.2 --MO oxides.

FIG. 5 is a three component phase diagram of SiO.sub.2 --TiO.sub.2 --XO oxides.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The basic construction of the monolithic ceramic capacitor according to the first embodiment of the present invention will be described hereinafter referring to the drawings. FIG. 1 is a cross section showing one example of the monolithic ceramic capacitor, FIG. 2 is a plane view showing the dielectric ceramic portion having inner electrodes of the monolithic ceramic capacitor in FIG. 1, and FIG. 3 is a disassembled perspective view showing the dielectric ceramic portion having inner electrodes of the monolithic ceramic capacitor in FIG. 1.

As shown in FIG. 1, the monolithic ceramic capacitor 1 according to the present embodiment is provided with a rectangular shaped monolithic ceramic body 3 obtained by laminating a plurality of dielectric ceramic layers 2a and 2b via inner electrodes 4. An outer electrode 5 is formed on both side faces of the monolithic ceramic body 3 so that the outer electrodes are electrically connected to each of the specified inner electrodes 4, on which a first plating layer 6 comprising nickel or copper is plated, and a second plating layer 7 comprising a solder or tin being further formed on the first plating layer.

The method for producing the monolithic ceramic capacitor 1 will be next described in the order of production steps.

At first, a raw material powder of barium titanate prepared by weighing and mixing in a given composition ratio is prepared as an essential component of the dielectric ceramic layers 2a and 2b.

Then, a slurry is prepared by adding an organic binder in this raw material powder and, after forming this slurry into a sheet, a green sheet for use in the dielectric ceramic layers 2a and 2b is obtained.

Next, an inner electrode 4 comprising nickel or a nickel alloy is formed on one principal face of the green sheet to serve as a dielectric ceramic layer 2b. Nickel or nickel alloys as base metals may be used for the material of the inner electrode 4 when the dielectric ceramic layers 2a and 2b are formed using the dielectric ceramic composition as described above but the invention is not limited thereto. The inner electrode 4 may be formed by a screen printing method, a deposition method or a plating method.

After laminating a required number of the green sheets for use in the dielectric ceramic layers 2b having the inner electrode 4, the green sheets are inserted between the green sheets having no inner electrode for use as the dielectric ceramic layers 2a, thus obtaining a raw monolithic body by press-adhering these green sheets. Then, this raw monolithic body is fired at a given temperature to obtain a ceramic monolithic body 3.

The outer electrodes 5 are formed at the both side faces of the ceramic monolithic body 3 so as to be electrically connected to the inner electrodes 4. The same material used in the inner electrodes 4 can be used for the outer electrodes 5. While silver, palladium, a silver-palladium alloy, copper and a copper alloy are available in addition to a composition prepared by adding a glass frit such as a B.sub.2 O.sub.3 --SiO.sub.2 --BaO glass or Li.sub.2 O--SiO.sub.2 --BaO glass to these metal powders, an appropriate material should be selected by taking the application and application site of the monolithic capacitor into consideration. While the outer electrodes 5 can be formed by coating the ceramic monolithic body 3 obtained by firing with a metal powder paste as a raw material followed by heat-adhering, it may also be formed by heat-adhering the metal powder paste simultaneously with the ceramic monolithic body 3.

The first plating layer 6 is then formed by applying a plating of nickel or copper on the outer electrode 5. Finally, the second plating layer 7 comprising a solder or tin is formed on the first plating layer 6, thereby completing the monolithic capacitor 1. Such process for further forming a conductive layer on the outer electrode 5 may be omitted depending on the intended application of the monolithic ceramic capacitor.

By using the dielectric ceramic composition as described previously for constructing the dielectric ceramic layers 2a and 2b, the characteristics of the dielectric ceramic layers are not deteriorated even when it is fired in a reducing atmosphere. In other words, such characteristics are obtained in which the product the insulation resistance and the electrostatic capacitance (the product CR) is as high as about 4900 to 5000 .OMEGA..cndot.F or more and about 200 .OMEGA..cndot.F or more at room temperature and 150.degree. C., respectively, when the capacitor is used under an electric field strength as high as about 10 kV/mm, while having a small voltage dependence of the insulation resistance, the absolute value of the capacitance decreasing ratio at an impressed DC voltage of 5 kV/mm being as small as about 40% to 45%, the insulation durability being as high as about 12 kV/mm or more under an AC voltage and about 14 kV/mm under a DC voltage, the temperature characteristics of the electrostatic capacitance satisfying the B-level characteristic standard stipulated in the JIS Standard in the temperature range of -25.degree. C. to +85.degree. C. and X7R-level characteristic standard stipulated in the EIA standard in the temperature range of -55.degree. C. to +125.degree. C. and having excellent weather resistance performance as shown by a high temperature load test at 150.degree. C. and at DC 25 kV/mm and a high humidity load test.

It has been confirmed that, among alkaline earth metal oxides such as SrO and CaO existing in barium titanate as impurities, alkali metal oxides such as Na.sub.2 O and K.sub.2 O and other oxides such as Al.sub.2 O.sub.3 and SiO.sub.2, the content of the alkali metal oxides especially influences the electric characteristics. While the specific dielectric constant is decreased when the amounts of addition of rare earth element oxides such as Eu.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, and Sc.sub.2 O.sub.3 and Y.sub.2 O.sub.3 are increased, the specific dielectric constant can be kept to a practically acceptable range of about 900 to 1600 by keeping the content of the alkali metal oxides contained in barium titanate as impurities to about 0.02% by weight or less, preferably 0.012% or less.

Adding an oxide represented by Li.sub.2 O--(Si, Ti)O.sub.2 --MO (wherein MO is at least one of Al.sub.2 O.sub.3 and ZrO.sub.2) to the dielectric ceramic composition allows the composition to be sintered at a relatively low temperature of about 1300.degree. C. or less, further improving the high temperature load characteristic.

Adding an oxide represented by Si.sub.2 O--TiO.sub.2 --XO (wherein XO is at least one of BaO, CaO, SrO, MgO, ZnO and MnO) to the dielectric ceramic composition allows the composition to be improved in sintering property as well as in high temperature load characteristics and humidity resistance load characteristics. A higher insulation resistance can be obtained by adding Al.sub.2 O.sub.3 and/or ZrO.sub.2 in the oxide represented by Si.sub.2 O--TiO.sub.2 --XO.

EXAMPLES

The present invention will now be described in more detail by way of examples. However, the present invention is not limited to these examples.

Example 1

After preparing and weighing TiCl.sub.4 and Ba(NO.sub.3).sub.2 having a variety of purity as starting materials, the compounds were precipitated as titanyl barium oxalate (BaTiO(C.sub.2 O.sub.4).cndot.4H.sub.2 O) by adding oxalic acid. This precipitate was decomposed by heating at a temperature of 1000.degree. C. or more to synthesize four kinds of barium titanate listed in TABLE 1.

TABLE 1 ______________________________________ Content of impurities (% by weight) Alkali Mean Kind of metal particle size BaTiO.sub.3 oxide SrO CaO SiO.sub.2 Al.sub.2 O.sub.3 (.mu.m) ______________________________________ A 0.003 0.012 0.001 0.01 0.005 0.6 B 0.02 0.01 0.003 0.019 0.008 0.56 C 0.012 0.179 0.018 0.155 0.071 0.72 D 0.062 0.014 0.001 0.019 0.004 0.58 ______________________________________

Oxides, carbonates or hydroxides of each component of the first side component were weighed so as to be in a composition ratio (mole ratio) of 0.25Li.sub.2 O-0.65(0.30TiO.sub.2 .cndot.0.70SiO.sub.2)-0.10Al.sub.2 O.sub.3 to obtain a powder by crushing and mixing.

Likewise, oxides, carbonates or hydroxides of each component of the second side component were weighed so as to be in a composition ratio (mole ratio) of 0.66SiO.sub.2 -0.17TiO.sub.2 -0.15BaO-0.02MnO to obtain a powder by crushing and mixing.

Oxide powders of the first and second side components were placed in separate platinum crucibles and heated at 1500.degree. C. After quenching and crushing the mixture, each oxide powder with a mean particle size of 1 .mu.m or less was obtained.

In the next step, BaCO.sub.3 for adjusting the mole ratio Ba/Ti (m) in the barium titanate, and Sc.sub.2 O.sub.3, Y.sub.2 O.sub.3, Eu.sub.2 O.sub.3, Gd.sub.2 O.sub.3, Tb.sub.2 O.sub.3 and Dy.sub.2 O.sub.3, BaZrO.sub.3, MgO and MnO, each having a purity of 99% or more, were prepared. These raw material powders and the oxides side components were weighted so as to form the compositions shown in TABLE 2 and TABLE 3. The amounts of addition of the first and second side components are indicated by parts by weight relative to 100 parts by weight of the essential component (BaO).sub.m TiO.sub.2 +.alpha.M.sub.2 O.sub.3 +.beta.R.sub.2 O.sub.3 +.gamma.BaZrO.sub.3 +gMnO+hMnO.

An organic solvent such as polyvinyl butyral binder and ethanol were added to the weighed compounds and the resulting mixture was mixed in a ball mill in an wet state to prepare a ceramic slurry. This ceramic slurry was formed into a sheet by the doctor blade method to obtain a rectangular shaped green sheet with a thickness of 35 .mu.m, followed by printing an electroconductive paste mainly composed of Ni on the ceramic green sheet to form an electroconductive paste layer for forming inner electrodes.

Then, a plurality of the ceramic green sheets on which the electroconductive layer had been formed were laminated so that the sides where the electroconductive paste is projected are alternately placed with each other, thus obtaining a monolithic body. This monolithic body was heated at 350.degree. C. in a N.sub.2 atmosphere and, after allowing the binder to decompose, the monolithic body was fired at the temperatures shown in TABLE 4 and TABLE 5 in a reducing atmosphere comprising H.sub.2 --N.sub.2 --H.sub.2 O gases under an oxygen partial pressure of 10.sup.-9 to 10.sup.12 MPa, thereby obtaining a ceramic sintered body.

Both side faces of the ceramic sintered body were coated with a silver paste containing B.sub.2 O.sub.3 --Li.sub.2 --SiO.sub.2 --BaO glass frit and fired at a temperature of 600.degree. C. in a N.sub.2 atmosphere, thereby obtaining outer electrodes electrically connected to the inner electrodes.

TABLE 2 - Amount of Amount of addition of (BaO).sub.m.TiO.sub.2 + .alpha.M.sub.2 O.sub.3 + .beta.R.sub.2 O.sub.3 + .gamma.BaZrO.sub.3 + gMgO + hMnO addition of the second Sample Kind of .alpha. Total of .beta. the first side side No. BaTiO.sub.3 Sc.sub.2 O.sub.3 Y.sub.2 O.sub.3 .alpha. Eu.sub.2 O.sub.3 Gd.sub.2 O.sub.3 Tb.sub.2 O.sub.3 Dy.sub.2 O.sub.3 Total of .beta. .alpha. + .beta. .gamma. g h g + h m component component *1 A 0 0.0008 0.0008 0 0.05 0 0 0.05 0.0508 0.02 0.05 0.07 0.12 1.005 1 0 *2 A 0.03 0.03 0.06 0 0 0.001 0 0.001 0.061 0.03 0.04 0.08 0.12 1.005 1 0 *3 A 0.01 0.01 0.02 0 0 0.0008 0 0.0008 0.0208 0.03 0.02 0.03 0.05 1.005 1 0 *4 A 0 0.001 0.001 0 0.03 0.02 0.02 0.07 0.071 0.03 0.03 0.1 0.13 1.01 1 0 *5 A 0.01 0.02 0.03 0.02 0 0 0.02 0.04 0.07 0.03 0.12 0.01 0.13 1.01 1 0 *6 A 0.01 0.01 0.02 0 0.02 0.02 0 0.04 0.06 0 0.07 0.06 0.13 1.01 1.5 0 *7 A 0 0.01 0.01 0 0 0 0.02 0.02 0.03 0.08 0.03 0.04 0.07 1.01 1.5 0 *8 A 0.01 0.02 0.03 0 0 0.01 0.01 0.02 0.05 0.02 0.001 0.069 0.07 1.01 1 0 *9 A 0.01 0 0.01 0.01 0 0 0 0.01 0.02 0.02 0.125 0.005 0.13 1.01 1 0 *10 A 0.01 0.01 0.02 0.01 0.01 0 0 0.02 0.04 0.02 0.079 0.001 0.08 1.01 1 0 *11 A 0.01 0 0.01 0 0.01 0 0.01 0.02 0.03 0.02 0.005 0.13 0.13 1.01 1 *12 A 0.01 0.02 0.03 0.02 0 0 0.02 0.04 0.07 0.03 0.05 0.08 0.14 1.01 1 0 *13 A 0.005 0.005 0.01 0 0.01 0.01 0 0.02 0.03 0.03 0.03 0.025 0.055 0.99 1 0 *14 A 0.01 0 0.01 0.01 0.005 0.005 0.01 0.03 0.04 0.04 0.04 0.03 0.07 1.00 1 0 *15 A 0.005 0.005 0.01 0 0 0.01 0 0.01 0.02 0.04 0.02 0.03 0.05 1.038 1 0 *16 A 0.01 0 0.01 0.01 0 0 0.01 0.02 0.03 0.02 0.03 0.02 0.05 1.05 0 1 *17 A 0 0.01 0.01 0 0 0.01 0.01 0.02 0.03 0.02 0.03 0.04 0.07 1.01 0 0 *18 A 0 0.01 0.01 0 0.01 0.01 0.01 0.03 0.04 0.02 0.04 0.03 0.07 1.01 5 0 *19 A 0 0.01 0.01 0.01 0.01 0 0 0.02 0.03 0.02 0.02 0.04 0.06 1.01 0 0 *20 A 0.01 0.01 0.02 0 0 0.01 0 0.01 0.03 0.02 0.03 0.02 0.05 1.01 0 4 *21 D 0 0.01 0.01 0 0.01 0.02 0 0.03 0.04 0.03 0.04 0.05 0.09 1.01 2 0 22 A 0 0.001 0.001 0.02 0 0.009 0 0.029 0.03 0.02 0.04 0.01 0.05 1.015 1 0 23 B 0.01 0.01 0.02 0 0.01 0 0 0.01 0.03 0.03 0.03 0.02 0.05 1.02 1

TABLE 3 - Amount of Amount of addition of (BaO).sub.m.TiO.sub.2 + .alpha.M.sub.2 O.sub.3 + .beta.R.sub.2 O.sub.3 + .gamma.BaZrO.sub.3 + gMgO + hMnO addition of the second Sample Kind of .alpha. Total of .beta. the first side side No. BaTiO.sub.3 Sc.sub.2 O.sub.3 Y.sub.2 O.sub.3 .alpha. Eu.sub.2 O.sub.3 Gd.sub.2 O.sub.3 Tb.sub.2 O.sub.3 Dy.sub.2 O.sub.3 Total of .beta. .alpha. + .beta. .gamma. g h g + h m component component 24 C 0.01 0.02 0.03 0 0 0 0.01 0.01 0.04 0.03 0.12 0.002 0.122 1.03 1 25 A 0.01 0.03 0.04 0 0 0.01 0 0.01 0.05 0.03 0.07 0.06 0.13 1.02 1 0 26 A 0.01 0.04 0.05 0 0.01 0 0 0.01 0.06 0.03 0.002 0.12 0.122 1.01 0 1 27 A 0.005 0.005 0.01 0 0 0 0.001 0.001 0.011 0.02 0.01 0.02 0.03 1.01 1 0 28 A 0 0.01 0.01 0.01 0.01 0 0 0.02 0.03 0.02 0.03 0.02 0.05 1.01 1 0 29 A 0 0.01 0.01 0.02 0 0.01 0 0.03 0.04 0.02 0.05 0.03 0.08 1.015 0 1 30 A 0 0.01 0.01 0 0.04 0 0 0.04 0.05 0.02 0.06 0.03 0.09 1.01 0 1 31 A 0 0.01 0.01 0 0.03 0 0.02 0.05 0.06 0.02 0.05 0.06 0.11 1.01 1 0 32 A 0.01 0.02 0.03 0 0 0.02 0 0.02 0.05 0.02 0.05 0.04 0.09 1.01 1 0 33 A 0.01 0.02 0.03 0 0 0 0.03 0.03 0.06 0.03 0.06 0.04 0.1 1.01 1 0 34 A 0 0.01 0.01 0 0.02 0 0 0.02 0.03 0.01 0.03 0.02 0.05 1.01 1 0 35 A 0.01 0.01 0.02 0.02 0 0 0 0.02 0.04 0.04 0.05 0.03 0.08 1.01 1 36 A 0.01 0.01 0.02 0 0.01 0.01 0 0.02 0.04 0.06 0.05 0.02 0.07 1.01 1 0 37 A 0.01 0.01 0.02 0 0 0.01 0.01 0.02 0.04 0.03 0.04 0.03 0.07 1.01 2 0 38 A 0.01 0.01 0.02 0.01 0 0 0 0.01 0.03 0.03 0.04 0.015 0.055 1.01 2 39 A 0.01 0.01 0.02 0 0.01 0 0 0.01 0.03 0.02 0.03 0.04 0.07 1.01 2 0 40 A 0 0.02 0.02 0 0 0.01 0 0.01 0.03 0.02 0.03 0.02 0.05 1.01 2 0 41 A 0 0.02 0.02 0 0 0 0.01 0.01 0.03 0.02 0.03 0.03 0.06 1.001 2 0 42 A 0.02 0 0.02 0.01 0.01 0 0 0.02 0.04 0.03 0.04 0.03 0.07 1.01 0 2 43 A 0.01 0.01 0.02 0 0 0.01 0.01 0.02 0.04 0.03 0.03 0.05 0.08 1.035 2 0 44 A 0.01 0.01 0.02 0 0.02 0 0 0.02 0.04 0.03 0.04 0.03 0.07 1.015 0.2 0 45 A 0.01 0.01 0.02 0 0 0 0.01 0.01 0.03 0.03 0.03 0.02 0.05 1.01 3 0 46 A 0 0.02 0.02 0 0 0 0.01 0.01 0.03 0.03 0.02 0.04 0.06 1.01 0 0.2 47 A 0 0.02 0.02 0.01 0 0.01 0 0.02 0.04 0.03 0.05 0.02 0.07 1.01 0 3

The overall dimensions of the monolithic ceramic capacitor thus obtained were 5.0 mm in width, 5.7 mm in length and 2.4 mm in thickness while the thickness of each dielectric ceramic layer was 30 .mu.m. The total number of the effective dielectric ceramic layers were 57, the area of the confronting electrode per layer being 8.2.times.10.sup.-6 m.sup.2.

Electric characteristics of these monolithic ceramic capacitors were measured. The electrostatic capacitance (C) and dielectric loss (tan .delta.) were measured using an automatic bridge type measuring instrument at 1 kHz, 1 Vrms and 25.degree. C. and the dielectric constant (.epsilon.) was calculated from the electrostatic capacitance. Next, the insulation resistance was measured using an insulation resistance tester at 25.degree. C. and 150.degree. C. by impressing direct current voltages of 315 V (or 10 kV/mm) and 945 V (or 30 kV/mm) for 2 minutes, obtaining the product of the electrostatic capacitance and insulation resistance, or the product CR.

The rate of change of the electrostatic capacitance against temperature changes was also measured. The rate of change at -25.degree. C. and 85.degree. C. by taking the electrostatic capacitance at 20.degree. C. as a standard (.DELTA.C/C.sub.20), the rate of change at -55.degree. C. and 125.degree. C. by taking the electrostatic capacitance at 25.degree. C. as a standard (.DELTA.C/C.sub.25) and the maximum value of the rate of change (.vertline..DELTA.C.vertline..sub.max) as an absolute value were measured as the electrostatic capacitances against temperature changes.

The DC vias characteristic was also evaluated. First, the electrostatic capacitance when an AC voltage of 1 kHz and 1 Vrms was impressed was measured. Then, the electrostatic capacitance when a DC voltage of 150 V and an AC voltage of 1 kHz and 1 Vrms were simultaneously impressed was measured, thereby the rate of reduction of the electrostatic capacitance (.DELTA.C/C) due to loading the DC voltage was calculated.

In the high temperature load test, a direct current voltage of 750 V (or 25 kV/mm) was impressed at 150.degree. C. on 36 pieces of each sample to measure the time dependent changes of the insulation resistance. The time when the insulation resistance of each sample was reduced below 10.sup.6 .OMEGA. was defined to be a life span time and mean life span time was evaluated.

In the humidity resistance test, the number of the test pieces having an insulation resistance of 10.sup.6 .OMEGA. or less among the 72 test pieces were counted after impressing a DC voltage of 315 V under an atmospheric pressure of 2 atm (relative humidity 100%) at 120.degree. C. for 250 hours.

Insulation breakdown voltages under AC and DC voltages were measured by impressing AC and DC voltages at a voltage increase rate of 100 V/sec.

The results described above are listed in TABLE 4 and TABLE 5.

TABLE 4 - DC vias Product CR (.OMEGA. .multidot. F) Humidity Ratio of Temperature Dependent Capacitor characteristic 315 V 945 V 315 V 945 V Insulation breakdown Resistance Baking Dielectric Change (%) (%) Impressed Impressed Impressed Impressed voltage Load Test: Sample Temp. Dielectric Loss .DELTA.C/C.sub.20 .DELTA.C/C.sub.25 Maximum .DELTA.C/C Voltage Voltage Voltage Voltage (kV/mm) Number of Mean Life No. (.degree. C.) Constant tan .delta. (%) -25.degree. C. 85.degree. C. -55.degree. C. 125.degree. C. value 5 kV/mm 25.degree. C. 150.degree. C. AC DC rejects Span *1 1300 1210 0.7 5.6 -12 6.4 -17.5 21 -21 5110 4860 220 210 12 14 0/72 960 *2 1300 960 0.7 2.3 -7.8 4.7 -6.9 8.7 -16 8520 8090 200 190 12 14 0/72 910 *3 1300 1550 0.7 3 -7.9 5 -6.8 8.5 -42 3020 2870 120 110 13 14 0/72 930 *4 1300 920 0.7 6 -12.9 7.5 -19 25.3 -14 5060 4810 250 240 12 14 0/72 120 *5 1280 960 2 2.1 -8 4.2 -7.1 8.5 -14 5070 4820 260 250 12 14 10/72 180 *6 1280 1070 0.7 1.9 -8.2 3 -7.5 8.9 -16 3120 2180 140 100 12 14 0/72 870 *7 1300 1440 0.7 2.2 -14.3 4.5 -31.5 36.2 -36 5160 4900 240 230 12 14 0/72 160 *8 1280 1280 0.8 2.2 -12.5 4.6 -16.3 21.3 -26 3090 2940 130 120 13 14 0/72 950 *9 1360 1530 2.6 2.3 -7.7 5 -7.5 8.5 -43 5110 4860 230 220 12 14 53/72 120 *10 U nmeasurable Due to Semiconductor Formation *11 1280 1460 0.7 3 -8.5 5.1 -17.9 23.6 -38 3150 2990 150 140 12 14 0/72 150 *12 1280 940 2.1 2.3 -8.2 4.5 -8.5 8.7 -14 5060 4800 240 230 12 14 9/72 100 *13 Unmeasurable Due to Semiconductor Formation *14 1300 1360 0.7 3.4 -8.4 5.3 -8 9.3 -30 3200 3040 160 150 10 11 0/72 1 30 *15 Unmeasurable Due to Insufficient Sintering *16 Unmeasurable Due to Insufficient Sintering *17 Unmeasurable Due to Insufficient Sintering *18 1300 1320 2.6 3.3 -8.3 5.1 -8.2 9.2 -25 3250 3090 170 160 11 12 0/72 150 *19 Unmeasurable Due to Insufficient Sintering *20 1300 1470 2.6 1.9 -8.7 4 -8 9.3 -41 3300 3140 180 170 12 12 0/72 110 *21 1300 1140 0.6 2.2 -8.9 7 -8.3 9.5 -26 5180 4920 280 270 12 14 0/72 860 22 1280 1480 0.7 5.2 -7.2 6.5 -7 8.7 -39 5090 4840 270 260 12 15 0/72 920 23 1280 1460 0.7 1.6 -7.6 7 -7.2 8.8 -39 5020 4770 250 240 12 14 0/72 940

TABLE 5 - DC vias Product CR (.OMEGA. .multidot. F) Humidity Ratio of Temperature Dependent Capacitor characteristic 315 V 945 V 315 V 945 V Insulation breakdown Resistance Baking Dielectric Change (%) (%) Impressed Impressed Impressed Impressed voltage Load Test: Sample Temp. Dielectric Loss .DELTA.C/C.sub.20 .DELTA.C/C.sub.25 Maximum .DELTA.C/C Voltage Voltage Voltage Voltage (kV/mm) Number of Mean Life No. (.degree. C.) Constant tan .delta. (%) -25.degree. C. 85.degree. C. -55.degree. C. 125.degree. C. value 5 kV/mm 25.degree. C. 150.degree. C. AC DC reject Span 24 1280 1350 0.6 1.7 -8.5 5.9 -7.8 8.9 -31 5280 5020 290 280 12 15 0/72 990 25 1300 1260 0.6 2 -8.7 5.1 -8.2 9.5 -23 5130 4870 270 260 12 14 0/72 890 26 1300 1080 0.7 2.1 -8.8 5.5 -8.3 9.2 -17 5200 4940 220 210 12 15 0/72 950 27 1300 1650 0.6 2.1 -7.5 6.1 -7.5 8.7 -45 5210 4950 230 220 12 14 0/72 820 28 1300 1410 0.7 3 -7.9 6.7 -7.3 8.8 -36 5290 5030 280 270 12 14 0/72 850 29 1280 1370 0.6 3.1 -8.2 6 -7.8 8.8 -33 5200 4940 290 280 13 14 0/72 900 30 1280 1230 0.6 2.1 -8.5 5.8 -7.9 9.5 -22 5260 5000 250 240 12 14 0/72 870 31 1300 1030 0.6 2 -8.9 5 -8.2 9.2 -15 5240 4980 210 200 12 14 0/72 920 32 1300 1260 0.6 1.9 -7.9 4.8 -7.5 8.7 -21 5010 4760 200 190 12 14 0/72 920 33 1300 1060 0.6 2 -8 4.9 -7.8 8.5 -16 5230 4970 260 250 12 14 0/72 870 34 1280 1420 0.6 2 -8.2 5.3 -7.9 8.9 -36 5060 4810 280 270 12 14 0/72 850 35 1280 1360 0.6 2 -7.8 5.7 -8 8.6 -30 5260 5000 230 220 12 15 0/72 820 36 1300 1370 0.7 2.5 -7.9 6 -7.6 8 -32 5100 4850 220 210 12 14 0/72 850 37 1300 1350 0.6 2 -8 6.1 -7.7 8.5 -32 5070 4820 250 240 12 14 0/72 890 38 1300 1470 0.6 2 -8.1 5.8 -8 8.6 -39 5090 4840 230 220 13 14 0/72 900 39 1280 1440 0.7 2.6 -8.1 5.9 -7.9 8.7 -39 5100 4850 240 230 13 14 0/72 870 40 1280 1480 0.7 2.5 -8.5 6 -8.2 9.2 -40 5210 4950 210 200 12 14 0/72 910 41 1280 1460 0.6 2 -7.8 6.7 -8 8.6 -40 5220 4960 260 250 12 14 0/72 890 42 1300 1380 0.6 2.7 -7.9 6 -8.2 8.7 -30 5160 4900 230 220 12 14 0/72 920 43 1300 1350 0.6 2 -8.1 5.8 -8 8.5 -30 5360 5090 250 240 12 14 0/72 900 44 1300 1320 0.6 2.5 -8.2 5.9 -7.7 8.9 -25 5180 4920 230 220 12 14 0/72 880 45 1300 1450 0.7 2.3 -8.3 7.2 -7.8 8.8 -38 5190 4930 290 280 12 14 0/72 850 46 1280 1430 0.7 2.3 -8 6.8 -7.9 8.8 -38 5230 4970 270 260 12 14 0/72 860 47 1300 1440 0.6 2.2 -7.9 6.5 -7.5 8 -38 5260 5000 260 250 12 14 0/72 920

It is evident from Table 1 to TABLE 5 that the monolithic ceramic capacitor according to the present invention has a capacitance decreasing ratio of as small as within -45% at an impressed voltage of 5 kV/mm and a dielectric loss of less than 1.0 %, wherein the rate of change of the electrostatic capacitance against temperature changes satisfies both the B-level characteristic standard stipulated in the JIS Standard in the temperature range of -25.degree. C. to +85.degree. C. and X7R-level characteristic standard stipulated in the EIA standard in the temperature range of -55.degree. C. to +125.degree. C.

Moreover, the insulation resistances at 25.degree. C. and 150.degree. C. as expressed by the product CR show values as high as 5000 .OMEGA..cndot.F or more and 200 .OMEGA..cndot.F or more, respectively, when the ceramic capacitor is used under a high electric field strength of 10 kV/mm. The insulation breakdown voltage also shows high values of 12 kV/mm or more under the AC voltage and 14 kV/mm or more under the DC voltage. In addition, an acceleration test at 150.degree. C. and DC 25 kV/mm gave a mean life span as long as 800 hours or more in addition to enabling a relatively low firing temperature of 1300.degree. C. or less.

The reason why the composition was limited in the present invention will be described hereinafter.

In the composition of (BaO).sub.m TiO.sub.2 +.alpha.M.sub.2 O.sub.3 +.beta.R.sub.2 O.sub.3 +.gamma.BaZrO.sub.3 +gMnO +hMgO (wherein M.sub.2 O.sub.3 represents at least one of Sc.sub.2 O.sub.3 or Y.sub.2 O.sub.3 and R.sub.2 O.sub.3 represents at least one of Eu.sub.2 O.sub.3, Gd.sub.2 O.sub.3, Tb.sub.2 O.sub.3 and Dy.sub.2 O.sub.3, .alpha., .beta., .gamma., g and h representing mole ratio, respectively), a M.sub.2 O.sub.3 content .alpha. of less than about 0.001 as shown in the sample No. 1 is not preferable because the temperature characteristic does not satisfy the B-level/X7R characteristics. On the other hand, a M.sub.2 O.sub.3 content .alpha. of more than about 0.05 as shown in the sample No. 2 is also not preferable because the specific dielectric constant is reduced to less than 1000. Accordingly, the preferable range ofthe M.sub.2 O.sub.3 content .alpha. is 0.001.ltoreq..alpha..ltoreq.0.05.

It is not preferable that the R.sub.2 O.sub.3 content .beta. is less than about 0.001 as in the sample No. 3 since the insulation resistance is so low that the product CR becomes small. It is also not preferable that the R.sub.2 O.sub.3 content .beta. is more than about 0.05 as in the sample No. 4 because the temperature characteristic does not satisfy the B-level/X7R characteristics, reducing reliability. Accordingly, the preferable range of the R.sub.2 O.sub.3 content .beta. is 0.001.ltoreq..beta..ltoreq.0.05.

When the combined amount of M.sub.2 O.sub.3 and R.sub.2 O.sub.3 (.alpha.+.beta.) is more than about 0.06, the dielectric loss is increased up to 2.0% while the mean life span is shortened, and the number of rejects in the humidity resistance load test is increased. Accordingly, the combined amount of M.sub.2 O.sub.3 and R.sub.2 O.sub.3 (.alpha.+.beta.) is preferably in the range of .alpha.+.ltoreq.0.06.

It is not preferable that, as seen in the sample No. 6, the BaZrO.sub.3 content .gamma. is zero since the insulation resistance becomes low while having a larger voltage dependency of the insulation resistance than in the system containing BaZrO.sub.3. On the other hand, when the BaZrO.sub.3 content .gamma. exceeds about 0.06 as in the sample No. 7, the temperature characteristic does not satisfy the B-level/X7R characteristics, and the mean life span is shortened. Accordingly, the preferable range of the BaZrO.sub.3 content .gamma. is 0.005.ltoreq..gamma..ltoreq.0.06.

It is not preferable that, as seen in the sample No. 8, the MgO content g is about 0.001 since the insulation resistance becomes low and the temperature characteristics do not satisfy the B-level/X7R characteristics. On the other hand, when the MgO content g exceeds about 0.12 as seen in the sample No. 9, the sintering temperature becomes high and the dielectric loss exceeds 2.0%, which is not preferable because rejection in the humidity resistance test are greatly increased while shortening the mean life span. Accordingly, the preferable range of the MgO content g is 0.001.ltoreq.g.ltoreq.0.12.

It is not preferable that, as seen in the sample No. 12, the MnO content h is about 0.001 as seen in the sample No. 10 since the sample becomes not measurable due to semiconductor formation. It is not preferable that the MnO content h exceeds about 0.12, on the other hand, b