DE69125016T2 - Laminated semiconductor ceramic capacitor with intergrain insulation and manufacturing process - Google Patents

Description

Background of the invention 1. Field of the invention:

The present invention relates to a laminated semiconductor ceramic capacitor having an intergrain insulation structure and a method for producing the same, and more particularly to a ceramic capacitor which absorbs both low-voltage noise and high-voltage noise under normal operating conditions and serves as a varistor against the intrusion of high-voltage pulses and high-voltage static electricity, thereby protecting built-in semiconductors and electronic equipment from being damaged by abnormal voltages caused by noise, pulses and static electricity generated in electronic equipment.

2. Description of the state of the art:

In recent years, semiconductor devices such as ICs and LSIs have been widely used in electronic equipment for the purpose of realizing multifunctional applications of the equipment and making the equipment light, small and easy to handle. However, the use of many semiconductor devices has caused a reduction in the noise resistance of the equipment. In order to maintain the noise resistance of the electronic equipment, bypass capacitors such as a film capacitor, a laminated ceramic capacitor and a semiconductor ceramic capacitor are used in power supply lines of various types of ICs and LSIs. These capacitors show excellent performance in absorbing low voltage noise and high voltage noise. However, these capacitors themselves have no effect in absorbing high voltage pulses and high voltage static electricity, so the intrusion of high voltage pulses and high voltage static electricity causes the malfunction of the equipment and the failure of semiconductors and/or capacitors.

As a new type of capacitor having sufficient pulse withstand capability and excellent pulse absorption capability as well as good noise absorption capability and stability with respect to temperature and frequency changes, a semiconductor ceramic capacitor having an intergrain insulation structure in which a SrTiO3 type semiconductor ceramic capacitor is given a varistor function has been developed (hereinafter, this type of capacitor is referred to as a ceramic capacitor with a varistor function). This type of ceramic capacitor is disclosed in Japanese Laid-Open Patent Publication Nos. 57-27001 and 57-35303. Usually, this ceramic capacitor with a varistor function absorbs low voltage noise and high voltage noise, and when high voltage pulses and high voltage static electricity enter it, the capacitor works as a varistor, thereby protecting the electronic equipment and built-in semiconductors from abnormal voltages caused by noise, pulses and static electricity generated in the electronic equipment. Thus, its application has expanded to various fields.

As electronic parts have been made lighter, smaller, more manageable and more powerful, there has been a strong demand for miniaturization and achieving high performance of ceramic capacitors with a varistor function. However, since a conventional ceramic capacitor with a varistor function is of a single plate type, so that the effective electrode surface becomes small when the capacitor is miniaturized, this results in a reduction in capacitance and low reliability. As a solution to the above problems, it is considered that the electrode area is increased by laminating electrodes which are formed as sheet structures.

In general, a capacitor having no lamination structure is manufactured by a method comprising the steps of: sintering a ceramic sheet under a reducing atmosphere to make the ceramics on the green sheet semiconductive; isolating a grain boundary portion of the semiconductive ceramics by oxidizing the green sheet in air; and applying an external electrode to the resulting green sheet. However, when this method is applied to the above-mentioned laminated capacitor, the following problems arise. When the green sheet is laminated with an internal electrode on its surface and sintered, cracks are generated or the internal electrode is oxidized during the oxidation step to be isolated due to the difference in the contraction coefficient between the internal electrode and the ceramics constituting the green sheet. Accordingly, it has been considered very difficult to manufacture a lamination type capacitor having a varistor function (hereinafter, this capacitor is referred to as a laminated ceramic capacitor having a varistor function) by simultaneously sintering a material of the ceramic capacitor having a varistor function and a material of the inner electrode, the material of the ceramic capacitor containing the green sheets and a material of the outer electrodes, etc., but not containing the material of the inner electrode.

As a method for simultaneously sintering a material of the laminated ceramic capacitor with varistor function and a material of the inner electrode, the following method for producing a laminated ceramic capacitor with varistor function has been developed and proposed, which uses methods disclosed in Japanese Laid-Open Patent Publications Nos. 54-53248 and 54-54250, comprising the steps of: printing a pattern corresponding to the inner electrode using organic binder-enriched ceramic paste on the surface of the ceramic substrate; sintering the ceramic substrate to make the pattern of the inner electrode porous; and impregnating the porous pattern with electrically conductive metals under the appropriate pressure, or alternatively a step of forming a pattern of the inner electrode by a gold plating or fusion process. However, these processes have many manufacturing difficulties and have not yet reached a practical standard.

Japanese Laid-Open Patent Publication No. 59-215701 discloses a method comprising the steps of: forming a green sheet made of ceramic powder calcined in a non-oxidizing atmosphere; printing an internal electrode pattern using an electrically conductive paste mixed with a diffusion material on the surface of the green sheet, the thermal diffusion material having the ability to form an electrically insulated layer in a grain boundary; and sintering the green sheet in the oxidizing atmosphere. Another method disclosed in Japanese Laid-Open Patent Publication No. 63-219115 comprises the steps of: forming a green sheet made of semiconductive ceramic powder as a main component, the main component being mixed with an oxidizing agent and/or a dispersing agent with a glass component for the purpose of forming an insulating layer; alternately laminating the green sheets with a plurality of internal electrodes; and sintering the laminated sheets in air or under the oxidizing atmosphere. However, according to the above two methods, the sintering temperature is relatively low in the range of 1,000 to 1,200 ºC, so that the ceramics are not easily sintered and crystal grains do not come into contact with each other. The resulting ceramic capacitor, which is an incompletely sintered body, has the following disadvantages, among others: a relatively low electric capacitance; a low value of the non-linear voltage index (the non-linear index is a representative factor for characterizing a varistor); and instability of the varistor voltage; and low Reliability as a capacitor. Moreover, Japanese Patent Laid-Open Publication No. 63-219115, which includes the step of adding a glass material to the ceramic powder as an additive, involves a problem that a glass phase is deposited in the crystal grain boundaries, whereby the electrical characteristics tend to deteriorate and the reliability of the capacitor deteriorates. Thus, this method has not yet reached a practical standard.

Thereafter, as described in Japanese Patent Application No. 1-36757, the present inventors have improved a method for producing a capacitor using a composition of SrTiO₃ containing an excess amount of Ti as a semiconductor component and MnO₂-SiO₂ compound types as a base material, and have made it possible to develop a laminated ceramic capacitor with a varistor function having internal electrodes made essentially of Au, Pt, Rh, Pd or Ni. Since Ni internal electrodes can cause oxidation of Ni at relatively low temperatures, thereby being easily insulated, a mixture of Ni and Pd or a SiTiO₃ containing a slight excess amount of Ti has been proposed for use as an internal electrode material. However, even in this case, it is difficult to achieve a fundamental solution to the above-mentioned disadvantages because Ni can be oxidized at re-oxidation temperatures of 1,200 ºC or higher.

As a patent concerning the laminated capacitors with varistor function, laminated nonlinear voltage elements made of ceramic material such as ZnO, Fe2O3 or TiO2 have been provided in Japanese Patent Publication No. 58-23921. This type of element has a very small capacitance. Therefore, although it has excellent performance with respect to pulses with relatively high voltage and absorption of static electricity, it has little effect with respect to noise with voltage lower than the varistor voltage or high frequency noise.

From EP 0 437 613 A1, EP 0 429 653 A1 and EP 0 412 167 A1, laminated semiconductor ceramic capacitors are known with an intergrain insulated structure comprising a plurality of Ni inner electrodes and outer electrodes, wherein the Ni inner electrodes are arranged in a substantially parallel manner in the ceramic block so as to reach the corresponding opposite edges of the ceramic block alternately one after the other, and wherein the outer electrodes are each electrically connected to the corresponding edges of the inner electrodes. A semiconductor ceramic capacitor is also known from DE 26 55 567 A1. The inner electrodes of this capacitor are also made of a transition metal, in particular Ni, and/or an alloy of a transition metal.

As described above, in the laminated ceramic capacitors with a varistor function using Ni for the internal electrodes, Ni is oxidized at relatively low temperatures. Therefore, depending on the manufacturing process, Ni is oxidized and the internal electrodes are insulated, whereby good electrical characteristics cannot be obtained. Accordingly, it is expected that new internal electrode compositions which prevent Ni from being oxidized and a method for manufacturing laminated ceramic capacitors with a varistor function using such Ni internal electrodes will be developed.

Summary of the invention

The laminated semiconductor ceramic capacitor having an intergrain insulated structure according to this invention, which overcomes the above-mentioned and many other disadvantages and deficiencies of the prior art, comprises a semiconductor ceramic block having an intergrain insulated structure, a plurality of Ni internal electrodes and external electrodes, the Ni internal electrodes being obtained from a paste containing a powder prepared by dissolving 0.05 mol% to 2.0 mol% of at least one compound containing an atom selected from the group containing Li, Na and K in Ni or a Ni-containing compound; the Ni internal electrodes are in a substantially arranged in parallel in the ceramic block so as to alternately reach the corresponding opposite edges of the ceramic block one after the other; and the outer electrodes are electrically connected to the corresponding edges of the inner electrodes, respectively.

In a preferred embodiment, the outer electrodes of the capacitor are made of at least one metal selected from the group consisting of Pd, Ag, Cu, Zn and Ni, an alloy of these materials or a mixture of these materials.

In a preferred embodiment, the external electrodes are obtained by dissolving at least one compound containing an atom selected from the group consisting of Li, Na and K, or a combination of at least one compound containing an atom selected from the group consisting of Li, Na and K and at least one compound containing a Pd atom or a Pt atom in Ni or a compound containing Ni.

In a preferred embodiment, the outer electrode comprises (1) lower outer electrodes obtained by dissolving at least one compound containing an atom selected from the group consisting of Li, Na and K, or a combination of at least one compound containing an atom selected from the group consisting of Li, Na and K and at least one compound containing a Pd atom or a Pt atom in Ni or a Ni-containing compound, and (2) upper outer electrodes of Ag or Ag-Pd type.

In the preferred embodiment, the outer electrodes are obtained by dissolving at least one compound containing a Pd atom or a Pt atom in Ni or a Ni-containing compound.

In a preferred embodiment, the external electrodes comprise (1) lower external electrodes obtained by dissolving at least one compound containing a Pd atom or a Pt atom in Ni or a Ni-containing compound, and (2) lower external electrodes of Ag or Ag-Pd type.

In a preferred embodiment, the intergrain-isolated semiconductor ceramic comprises as a main component SrTiO₃ containing an excess amount of Ti so as to provide a molar ratio of Sr to Ti in the range of 0.95 ≤ Sr/Ti < 1.00; at least one compound selected from the group consisting of Nb₂O₅, Ta₂O₅, V₂O₅, W₂O₅, Dy₂O₃, Nd₂O₃, Y₂O₃, La₂O₃ and CeO₂ in the range of 0.05 to 2.0 mol%; and a combination of at least one compound containing a Mn atom and at least one compound containing a Si atom, the total amount of the combination being in the range of 0.2 to 5.0 mol%, each in terms of MnO₂ and SiO₂.

In a preferred embodiment, the intergrain-isolated semiconductor ceramic further comprises at least one compound selected from the group consisting of Na₂SiO₃ and Li₂SiO₃ in the range of 0.05 to 2.0 mol%; at least one compound selected from the group consisting of Na₂SiO₃ and Li₂SiO₃ in the range of 0.05 to 2.0 mol%, and Al₂O₃ in the range of 0.05 to 2.0 mol%; or at least one compound selected from the group consisting of NaAlO₂ and LiAlO₂ in the range of 0.05 to 4.0 mol%.

Instead of the above mentioned SrTiO₃, Sr(1-x)BaxTiO₃ or Sr(1-x)CaxTiO₃ can be used.

Various methods for producing a semiconductor ceramic capacitor with an intergrain insulated structure are defined by the independent method claims 19 to 28.

The methods claimed therein make it possible to achieve the following objects: (1) providing a laminated semiconductor ceramic capacitor with an intergrain-insulated structure having a varistor function, which absorbs low-voltage noise and high-voltage noise under normal operating conditions and which functions as a varistor when high-voltage pulses and high-voltage static electricity enter the circuit; (2) providing a laminated semiconductor ceramic capacitor with an intergrain-insulated structure having a varistor function, which contains SrTiO₃ as a main component, in which the ceramic capacitor material and the inner electrode material are sintered simultaneously; (3) providing a laminated semiconductor ceramic capacitor with an intergrain-insulated structure having a varistor function, which comprises Ni as inner electrodes; and (4) providing a method for manufacturing a laminated semiconductor ceramic capacitor having an intergrain insulated structure with a varistor function, which has the above-mentioned characteristics.

Short description of the drawings

The present invention will be better understood by those skilled in the art and its numerous objects and advantages will become apparent by referring to the accompanying drawings in which:

Figure 1 is a flow chart showing a process for producing a laminated ceramic capacitor with a varistor function according to Example 1 of the present invention;

Figure 2 is an exploded perspective view showing an example of the laminated ceramic capacitor with varistor function according to the present invention, as well as laminated green sheets and a pattern of an internal electrode paste printed on the green sheets;

Figure 3 is a partially cutaway view of the laminated ceramic capacitor with varistor function obtained in Examples 1 to 7 of the present invention;

Figure 4 is a flow chart showing a process for producing a laminated ceramic capacitor with a varistor function according to Example 2 of the present invention;

Figure 5 is a flow chart showing a process for producing the laminated ceramic capacitor with varistor function according to Examples 3 and 4 of the present invention;

Figure 6 is a flow chart showing a process for producing the laminated ceramic capacitor with varistor function according to Example 5 of the present invention;

Figure 7 is a flow chart showing a process for producing the laminated ceramic capacitor with varistor function according to Example 6 of the present invention;

Figure 8 is a flow chart showing a process for producing the laminated ceramic capacitor with varistor function according to Example 7 of the present invention;

Figure 9 is a partially cutaway view showing a laminated ceramic capacitor having a varistor function obtained according to Examples 8 to 21 of the present invention;

Figure 10 is a flow chart showing a process for producing the laminated ceramic capacitor with varistor function according to Example 8 of the present invention;

Figure 11 is a flow chart showing a process for producing the laminated ceramic capacitor with varistor function according to Example 9 of the present invention;

Figure 12 is a flow chart showing a process for producing the laminated ceramic capacitor having a varistor function according to Example 10 of the present invention;

Figure 13 is a flow chart showing a process for producing the laminated ceramic capacitor with varistor function according to Example 11 of the present invention;

Figure 14 is a flow chart showing a process for producing the laminated ceramic capacitor with varistor function according to Example 12 of the present invention;

Figure 15 is a flow chart showing a process for producing the laminated ceramic capacitor with varistor function according to Example 13 of the present invention;

Figure 16 is a flow chart showing a process for producing the laminated ceramic capacitor with varistor function according to Example 14 of the present invention;

Figure 17 is a flow chart showing a process for producing the laminated ceramic capacitor with varistor function according to Example 15 of the present invention;

Figure 18 is a flow chart showing a process for producing the laminated ceramic capacitor with varistor function according to Example 16 of the present invention;

Figure 19 is a flow chart showing a process for producing the laminated ceramic capacitor with varistor function according to Example 17 of the present invention;

Figure 20 is a flow chart showing a process for producing a laminated ceramic capacitor having a varistor function according to Example 18 of the present invention;

Figure 21 is a flow chart showing a process for producing the laminated ceramic capacitor with varistor function according to Example 19 of the present invention;

Figure 22 is a flow chart showing a process for producing the laminated ceramic capacitor with varistor function according to Example 20 of the present invention;

Figure 23 is a flow chart showing a process for producing the laminated ceramic capacitor with varistor function according to Example 21 of the present invention.

Description of the preferred embodiments

When manufacturing a ceramic capacitor with a varistor function, a ceramic element which is made semiconductive under a reducing or nitrogen atmosphere should be subjected to heat treatment in air (hereinafter, this heat treatment is referred to as re-oxidation) to provide its crystal grain boundaries with high resistance. Therefore, the following two facts are the most important when manufacturing a laminated ceramic capacitor with a varistor function: First, the internal electrodes are excellent in their resistance to oxidation; and second, the crystal grain boundaries of the ceramic element are excellent in their oxidation properties. This means that the internal electrodes and the ceramic element require opposite properties in the re-oxidation process.

Therefore, when a laminated ceramic capacitor having a varistor function with Ni internal electrodes is manufactured according to the present invention, the following facts must be considered. The oxidation resistance of the Ni internal electrodes should be improved and at the same time, the oxidation properties of the crystal boundaries of a ceramic element should also be improved. The inventors have found that (1) the oxidation resistance of the Ni internal electrodes is improved by dissolving at least one compound containing an atom selected from the group consisting of Li, Na and K in Ni or a Ni-containing compound, producing a P-type oxide to reduce the oxidation rate; and (2) at least one atom selected from the group consisting of Li, Na and K added to the Ni internal electrodes is easily dissolved in the crystal boundaries of a Ceramic element and the re-oxidation step and acts as an oxygen carrier, thereby accelerating the oxidation of the crystal boundaries.

According to the present invention, it is possible to improve both the oxidation resistance of the Ni internal electrodes and the oxidation properties of the crystal boundaries of a ceramic member by dissolving at least one compound containing an atom selected from the group consisting of Li, Na and K in Ni or a compound containing Ni, making it possible to easily manufacture a laminated ceramic capacitor with a varistor function having Ni internal electrodes.

Examples

The present invention is described by illustrating the following examples.

example 1

First, a Li₂CO₃ powder in the range of 0.05 to 2.5 mol% was added to a NiO powder having an average particle size of 0.5 μm or less and a purity of 90%, and the mixture was calcined in air at a temperature in the range of 500 to 1,300 °C. The calcined powder was again finely ground so as to have an average particle size of 1.5 μm or less and provided as a raw material for the internal electrodes. The powdery raw material was dispersed in a solution together with an organic binder such as butyral resin to form an internal electrode paste. Then, as shown in Figure 2, 97 mol% of SrTiO₃ was added. (Sr/Ti =0.97) powder, 1 mol% Nb₂O₅ powder, 1 mol% MnO₂ powder and 1 mol% SiO₂ powder were mixed and formed into green sheets 1b having a thickness of about 50 µm by the doctor blade method, followed by cutting to a predetermined size. As shown in Figure 2, the internal electrode paste 2 were not printed on the uppermost and lowermost green sheets 1a and 1c. Usually, a plurality of green sheets 1b are laminated. The patterns of the internal electrode paste 2 were printed on the intermediate layers of the laminated sheets 1 so as to reach an edge of the sheet, and the green sheets 1b were stacked in such a manner that the edges reaching the internal electrodes were alternately superimposed and the edges not reaching the internal electrodes were alternately superimposed. Then, the uppermost and lowermost green sheets 1a and 1c were respectively set on the uppermost and lowermost parts, and the green sheets 1b on which the above internal electrode paste was printed were laminated therebetween. The resulting green laminated sheets 1b were heat-pressed and brought into contact with the uppermost and lowermost green sheets 1a and 1c to obtain a laminated body 1. The laminated body 1 was heated at a temperature in the range of 600 to 1,250 °C in air so as to remove the above binder therefrom, thereby calcining the laminated body. The calcined body was next sintered by heating at a temperature in the range of 1,200 to 1,350 °C in a reducing atmosphere, followed by re-oxidation by heating at a temperature of 900 to 1,100 °C in air. As shown in Fig. 3, the external electrode paste containing Ag was coated on both edges of the semiconductor ceramic having an intergrain insulated structure (hereinafter, this semiconductor ceramic is referred to as a ceramic element) in which terminals of the internal electrodes 2a were alternately exposed to opposite directions, and the Ag paste was baked by heating at 800 °C for 15 minutes in air, thereby obtaining a laminated ceramic capacitor 4 having a varistor function, which comprised a plurality of internal electrodes 2a in the ceramic element, the terminals of the internal electrodes 2a reaching each opposite edge of the ceramic element alternatively one after another, and external electrodes 3 arranged at opposite edges of the ceramic element so that the external electrodes 3 can be electrically connected to the terminals of the internal electrodes 2a.

The size of the laminated ceramic capacitor with varistor function, abbreviated as Type 5.5, is 5.70 mm in width, 5.00 mm in length and 2.00 mm in thickness. The capacitor is constructed of 10 layers on which patterns of the internal electrodes are printed. Figure 1 is a flow chart showing a manufacturing process according to the present invention.

For the laminated ceramic capacitor with varistor function thus prepared, various kinds of electrical properties such as a capacitance, tangent δ, a varistor voltage, a non-linear voltage index α, an equivalent series resistance (ESR), a capacitance temperature change rate, and a temperature coefficient of varistor voltage are shown in Tables 1 to 5, which vary with the re-oxidation temperatures.

The experimental conditions for preparing laminated samples were 1,200 ºC, 2 h for binder removal and calcination in air; and 1,300 ºC, 2 h for sintering in a reducing atmosphere of N2:H2 = 99:1. The internal electrode paste contains a powder prepared by calcining a mixed powder of NiO and Li2CO3 (the amount of Li2CO3 is 0 to 2.5 mol%, based on the total number of moles of NiO and Li2CO3) at 1,100 ºC for 2 h in air.

The respective electrical characteristics were obtained under the following experimental conditions.

* The capacitance (C) was measured at 1.0 V and 1.0 kHz.

* The varistor voltage V0.1mA was measured at 0.1 mA.

* The non-linear voltage index α was calculated from the values of the varistor voltage measured at 0.1 mA and 1.0 mA, using the following equation:

α; = 1 / log (V1mA/V0.1mA)

* The equivalent series resistance (ESR) is defined as the resistance at the resonance frequency, measured at 1.0 V.

* The capacitance temperature change rate was obtained from the following equation:

Capacity temperature change rate (%) =

Capacity at 85 ºC - (Capacity at -25 ºC)/Capacity at -25 ºC x 100

* The temperature coefficient of varistor voltage was obtained by the following equation:

Temperature coefficient of varistor voltage =

Varistor voltage at 50 ºC - Varistor voltage at 25 ºC/ (50 - 25) x Varistor voltage at 25 ºC x 100 Table 1 Table 2 Table 3 Table 4 Table 5

The samples marked by the symbol * in Tables 1 to 5 are comparative examples. The Ni inner electrodes of these sintered elements marked by the symbol * are noticeably oxidized. The capacitor with these inner electrodes cannot exhibit the performance of both a normal capacitor that absorbs low-voltage noise and high-voltage noise and a varistor that absorbs high-voltage pulse and high-voltage static electricity simultaneously. In addition, this type of capacitor has a high capacitance-temperature change rate and a high temperature coefficient of varistor voltage due to the presence of unreacted Li ions, whereby the reliability and electrical characteristics of the capacitor tend to be affected by temperature changes. Therefore, these samples are not suitable as a ceramic capacitor with varistor function that protects semiconductors and electronic equipment from abnormal voltages such as noise, pulses and static electricity generated in the electronic equipment. On the other hand, the samples not marked with the symbol * have a high capacitance, a high value of the non-linear voltage index α and a low equivalent series resistance (ESR). A capacitor with these characteristics exhibits the performances of both a normal capacitor that absorbs high-voltage noise and low-voltage noise and a varistor that absorbs high-voltage pulses and high-voltage static electricity. In addition, this type of capacitor has a low capacitance-temperature change rate and a low coefficient of varistor voltage, which means that reliability and electrical characteristics are not prone to being affected by temperature changes. Therefore, these samples are well suited for use as a ceramic capacitor with varistor function, which protects semiconductors and electronic equipment from abnormal voltages such as noise, pulses and static electricity generated in the electronic equipment.

The amount of Li₂CO₃ contained in the internal electrode paste of this example was set in the range of 0.05 to 2.0 mol% based on the total number of moles of NiO and Li₂CO₃ for the following reasons. If the amount of Li₂CO₃ is less than 0.05 mol%, the effect of the added material can hardly be achieved and the Ni internal electrodes are noticeably oxidized as the re-oxidation temperature increases. On the other hand, if the amount of Li₂CO₃ is greater than 2.0 mol%, the presence of a large amount of unreacted Li ions may affect the electrical characteristics and reliability of the resulting laminated ceramic capacitor. Therefore, it is seen that if the amount of Li₂CO₃ is less than 0.05 mol%, the effect of the added material can hardly be achieved and the Ni internal electrodes are noticeably oxidized as the re-oxidation temperature increases. is in the range of 0.05 to 2.0 mol%, (1) the oxidation resistance of the Ni internal electrodes is improved, (2) Li atoms are easily dispersed in the crystal boundaries of the ceramic element and act as oxygen carriers, thereby accelerating the oxidation of the crystal boundaries, resulting in the improvement of the varistor function of the laminated ceramic capacitor, and (3) the capacitance-temperature change rate and the temperature coefficient of varistor voltage of the resulting laminated semiconductor capacitor are also improved. For these reasons, it is expected that varying the amount of Li₂CO₃ added to the internal electrode paste provides a laminated ceramic capacitor with varistor function which has different electrical properties and excellent temperature characteristics.

Although a mixture of NiO and Li₂CO₃ was used as a powdery raw material as the internal electrode paste in this example, NiO may be replaced by Ni or Ni-containing carbonates, hydroxides, nitrates or the like. Li₂CO₃ may be replaced by Li-containing oxides, hydroxides, fluorides, silicates, aluminates or the like; and Li may be replaced by Na-containing or K-containing oxides, hydroxides, fluorides, silicates, aluminates or the like, which produces the same effect as achieved here.

Also, a mixture of two or more types of Li, Na or K can be used in this material.

Although Ag was used as the external electrode material in this example, it was confirmed that other materials such as Pd, Cu, Zn and Ni can provide the same effect. This means that at least one metal selected from the group consisting of Pd, Ag, Cu, Zn and Ni, an alloy thereof or a mixture thereof can be used as the external electrode material. Furthermore, it was confirmed that Ni external electrodes made of an external electrode paste prepared by dissolving at least one compound containing an atom selected from the group consisting of Li, Na and K in Ni or a Ni-containing compound can provide the same effect.

It was also confirmed that Ni external electrodes made from an external electrode paste prepared by dissolving a combination of at least one compound containing an atom selected from the group consisting of Li, Na and K and at least one compound containing a Pd atom or a Pt atom in Ni or a Ni-containing compound can achieve the same effect.

However, when an atom such as Cu, Zn and Ni is present in the external electrodes, it is necessary to lower the baking temperature, shorten the baking time and control the atmosphere in which the baking is carried out, because these atoms tend to be oxidized.

The effect of surge current withstand capability (maximum current wave value observed under the condition that the variation of varistor voltage V0.1mA is within ±10% when 8 x 20 µs pulse current is applied twice in a 5 min interval in the same direction) of the samples obtained in this example was measured in the range of 300 to 400 A, indicating the same or better characteristics as conventional ZnO type varistors.

It was also found that the laminated ceramic capacitor having the internal electrodes of the present invention had an excellent effect in withstanding power against surge current compared with those having internal electrodes of the same structure composed of Au, Pt, Rh, Pd and the like for the following reasons. At least one atom selected from the group consisting of Li, Na and K supplied to the internal electrodes forms (1) a solid insulated layer in the grain boundaries of a ceramic element and acts as a sintering aid to provide (2) a strong adhesion between the internal electrodes and the ceramic element. Thus, because of the above solid insulated layer, the laminated ceramic capacitor is not likely to be destroyed, and flashover is hardly generated because of the strong adhesion between the internal electrodes and the ceramic element.

The laminated ceramic capacitor with a varistor function thus manufactured has a larger capacitance and exhibits much better temperature and frequency characteristics than the laminated varistor disclosed in the above-mentioned Japanese Patent Publication No. 58-23921. The laminated ceramic capacitor of the present invention is manufactured by laminating ceramic capacitor materials with a varistor function which can form a capacitor having functions of both a normal noise absorbing capacitor and a varistor which absorbs impulses and static electricity, while the above-mentioned prior art varistor is simply made of stacked varistor materials which exhibit excellent surge current absorption capability. The laminated ceramic capacitor with a varistor function according to the present invention is completely different from the prior art varistor in both functions and use.

Example 2

A laminated body prepared by using green sheets and an internal electrode paste having the same composition as in Example 1 was heated at a temperature in the range of 600 to 1,250 °C in air to remove the binder, thereby calcining the laminated body. The calcined body was sintered by heating at a temperature in the range of 1,000 to 1,200 °C in a nitrogen atmosphere and then at a temperature in the range of 1,200 to 1,350 °C in a reducing atmosphere, followed by re-oxidation by heating at a temperature of 900 to 1,100 °C in air. Then, the external electrode paste containing Ag was coated on both edges of the ceramic element in which terminals of the internal electrodes were alternately exposed to opposite directions, and the Ag paste was baked by heating at 800 ºC for 15 min in air, thereby obtaining a laminated ceramic capacitor with a varistor function. The various electrical characteristics of the resulting laminated ceramic capacitor with a varistor function are shown in Tables 6 to 10.

The experimental conditions for preparing laminated samples were 1,200 ºC, 2 h for calcination in air; a total of 2 h for heating at 1,200 ºC in a nitrogen atmosphere and at 1,300 ºC in the reducing atmosphere of N₂:H₂ = 99:1; and 900 - 1,100 ºC, 2 h for re-oxidation in air. Also, the internal electrode paste and the external electrode paste were prepared by calcining a mixed powder of NiO and Li₂CO₃ at 1,100 ºC for 2 h in air. Figure 4 is a flow chart showing the preparation process.

The other manufacturing conditions, such as the number of laminated sheets, were identical to those in Example 1, and various electrical properties were measured as described therein. Table 6 Table 7 Table 8 Table 9 Table 10

It was confirmed that preheating in a nitrogen atmosphere during the sintering step of Example 2 (1) delayed, as intended, the time at which sintering and reduction of Ni contained in the inner electrode material were completed and brought it close to the time at which sintering of the ceramic element was completed, preventing delamination of the laminated body; and (2) controlled expansion and shrinkage of the inner electrode material caused by inclusion of H2 gas in Ni, preventing disconnection of the electrical connection of the inner electrodes and imperfect contact between outer electrodes and inner electrodes. Therefore, the laminated ceramic capacitor with varistor function of Example 2 is expected to have improved capacitance and performance in terms of surge withstand capability (350 to 500 A).

The same electrode paste as in Example 1, prepared by dissolving at least one compound containing an atom selected from the group containing Li, Na and K in Ni or Ni-containing compound, and a Outer electrode with the same structure as in Example 1 can also be used in Example 2.

Example 3

Patterns of an internal electrode paste obtained by adding 0.5 mol% Li₂CO₃ to NiO and dispersed in a binder were printed on green sheets having the same ceramic composition as in Examples 1 and 2 to form a laminated body. An external electrode paste obtained by adding Li₂CO₃ to NiO and dispersed in a binder was coated on both edges of the ceramic member of the laminated body in which terminals of the internal electrodes were alternately exposed in opposite directions, heated at a temperature in the range of 600 to 1,250 °C in air to remove the binder, thereby calcining the laminated body. Then, the laminated body was sintered at a temperature in the range of 1,200 to 1,350 ºC in a reducing atmosphere, re-oxidized at a temperature of 900 to 1,100 ºC in air after sintering, and re-reduced at a temperature of 350 to 800 ºC in a reducing atmosphere to obtain a laminated ceramic capacitor with a varistor function.

The electrical properties of the laminated ceramic capacitor thus obtained are shown in Table 11. The experimental conditions for preparing the laminated samples were 1,200 ºC, 2 h for removing the binder and calcining in air; 1,300 ºC, 2 h for sintering in the reducing atmosphere of N2:H2 = 99:1; 900 ºC, 2 h for re-oxidation in air; and 400 ºC, 30 min for re-reduction in the reducing atmosphere of N2:H2 = 99:1. Also, the inner electrode paste and the outer electrode paste were prepared by calcining a mixed powder of NiO and Li2CO3 at 1,100 ºC for 2 h in air. Figure 5 is a flow chart showing this manufacturing process.

The other manufacturing conditions, such as the number of laminated sheets, were identical to those of Examples 1 and 2, and various electrical properties were measured as described therein. Table 11

In Example 3, it was found that a laminated ceramic capacitor having a varistor function can be readily manufactured using the manufacturing method as shown in Figure 5. Since the Ni of the outer electrodes is oxidized to NiO after the re-oxidation of the ceramic element in Example 3, the outer electrode functions were lost due to the increased resistance value. Therefore, a step for reducing NiO to Ni in the outer electrodes (hereinafter referred to as re-reduction step) is the most important step in Example 3. The outer electrodes were re-reduced at 400 °C for 30 minutes in the reducing atmosphere of N₂:H₂=99:1 in this example. It was found that when re-reducing was carried out at a low temperature or in a reducing atmosphere containing a lower H₂ concentration, oxidized portions remained on the surface of the outer electrodes. When the Re-reduction temperature 700 ºC, not only the outer electrodes but also the ceramic element are undesirably reduced. For this reason, the re-reduction time should be shortened. The optimal re-reduction temperature was in the range of 400 to 600 ºC according to the experiment results.

The effect of the surge current resistance of the laminated ceramic capacitor with varistor function was remarkably reduced to 200 A when the amount of Li₂CO₃ added to the outer electrodes exceeded 1.0 mol% (300 to 400 A for 1.0 mol% or less of Li₂CO₃). The reason for this is that when both the outer electrode material and the ceramic material are sintered simultaneously as shown in Example 3, the increase in the amount of Li₂CO₃ added to the outer electrodes may accelerate the sintering properties of Ni and cause tensile stress in the vicinity of the outer electrodes in the ceramic element, which may cause the generation of microcracks and the reduction of the effect of the surge current resistance of the laminated ceramic capacitor. This phenomenon is related to the thickness of the coated external electrode paste. The preferable effect in surge current resistance is achieved as the thickness of the coated external electrode paste becomes thinner. Therefore, the thickness of the coated external electrode paste should be controlled to a certain level when the amount of Li₂CO₃ added is greater than 1.0 mol%.

Although a mixture of NiO with Li₂CO₃ was used as a powdery raw material for an internal electrode paste and an external electrode paste in Example 3, as stated in Example 1, a powdery raw material for the internal and external electrode paste obtained by dissolving at least one compound containing an atom selected from the group consisting of Li, Na and K in Ni or a compound containing Ni can be used.

Also, as indicated in Example 1, a powdery starting material for an external electrode paste can be used, which is obtained by dissolving a Combination of at least one compound containing an atom selected from the group consisting of Li, Na and K and at least one compound containing a Pd atom or a Pt atom in Ni or a Ni-containing compound.

Example 4

A laminated ceramic capacitor having a varistor function was manufactured by using an electrode paste obtained by further adding Pd to the external electrode paste of Example 3, i.e., by further adding Pd to the external electrode paste in which 0.5 mol% of Li₂CO₃ is added to NiO, according to a manufacturing method as shown in Figure 5. The electrical characteristics of the laminated ceramic capacitor thus obtained are shown in Table 12.

The other manufacturing conditions such as the number of laminated layers were identical to those of Examples 1 to 3, and various electrical properties were measured as described therein. Table 12

It was confirmed that the laminated ceramic capacitor with a varistor function according to Example 4, which was prepared by using an outer electrode material obtained by adding Pd and Li₂CO₃ to NiO, had a smaller Tan δ and a lower equivalent series resistance (ESR) compared with the capacitor of Example 3. This was because the supplied Pd acts as a reducing agent which can control oxidation on the surface of the outer electrodes and thus reduce their resistance value. It was also confirmed that the same effect of this additive could be obtained when Pt or a mixture of Pd and Pt was added to the outer electrode material.

Although a mixture of NiO and Li2CO3 was used as a powdery raw material for an internal electrode paste in Example 4, a powdery raw material obtained by dissolving at least one compound containing an atom selected from the group consisting of Li, Na and K in Ni or a Ni-containing compound can be used as an internal electrode paste as shown in Example 1.

Moreover, as stated in Example 1, although a mixture of NiO, Li₂CO₃ and Pd was used as the powdery raw material for the external electrode paste in Example 4, a powdery raw material obtained by dissolving a combination of at least one compound containing an atom selected from the group consisting of Li, Na and K and at least one compound containing a Pd atom or a Pt atom in Ni or a Ni-containing compound can be used as the external electrode paste.

Example 5

The sintering step of Example 3 was replaced by a first heating in a nitrogen atmosphere at an elevated temperature of 1,000 to 1,200 ºC and then in a reducing atmosphere at 1,200 to 1,350 ºC. The same re- Oxidation and re-reduction steps as in Example 3 were used to fabricate a laminated ceramic capacitor with varistor function. Figure 6 is a flow chart showing this fabrication process.

The other manufacturing conditions such as the number of laminated sheets were identical to those of Examples 1 to 4, and various electrical properties were measured as described therein.

Almost the same electrical properties as in Example 4 were obtained, except that the laminated ceramic capacitor of Example 5 had improved capacitance and a better effect in withstanding surge current (350 to 500 A) compared with that of Example 3. This was because preheating in a nitrogen atmosphere during the sintering step prevented delamination of the capacitor, dissolution of electrical connections of the internal electrodes and incomplete contact between the internal electrodes and the external electrodes, as stated in Example 2.

It was confirmed that when the outer electrodes of Example 4 containing Pd were used in Example 5, the resulting laminated ceramic capacitor with varistor function had a lower tan δ and equivalent series resistance (ESR) as well as an improved capacitance and surge current resistance. It was also confirmed that this effect of the additive could also be obtained when not only Pd but Pt or a mixture of Pd and Pt was used.

Example 6

A laminated body prepared by printing patterns with an internal electrode paste in which 0.5 mol% of Li₂CO₃ was added to NiO and dispersed in a binder on green sheets having the same composition as in Examples 1 to 5 was heated to a temperature in the range from 600 to 1,250 ºC in air so as to remove the binder, whereby the laminated body was calcined. Then, an outer electrode paste having the same composition as that of the inner electrode paste was coated on both edges of the inner electrodes of the calcined body in which terminals of the inner electrodes were alternately exposed in different directions. The calcined body was next sintered at a temperature in the range of 1,200 to 1,350 ºC in a reducing atmosphere. The calcined body was re-oxidized by heating at a temperature of 900 to 1,100 ºC in air and then re-reduced at a temperature of 360 to 800 ºC in a reducing atmosphere to prepare a laminated ceramic capacitor having a varistor function. The electrical characteristics of the laminated ceramic capacitor thus obtained are shown in Table 13. The experimental conditions for preparing the laminated sample were 1,200 °C, 2 h for binder removal and calcination in air; 1,300 °C, 2 h for sintering in the reducing atmosphere of N₂:H₂ = 99:1; 900 °C, 2 h for re-oxidation in air; and 400 °C, 30 min for re-reduction in the reducing atmosphere of N₂:H₂ = 99:1. Also, the inner electrode paste and the outer electrode paste were prepared by using a powder obtained by calcining a mixed powder of NiO and Li₂CO₃ at 1,100 °C for 2 h in air. Figure 7 is a flow chart showing this preparation process.

The other manufacturing conditions, such as the number of laminated sheets, were identical to those of Examples 1 to 5, and various electrical properties were measured as described therein. Table 13

The surge current withstand performance for this laminated ceramic capacitor was 300 to 400 A.

Example 7

The sintering step of Example 6 was replaced by first heating in a nitrogen atmosphere at an elevated temperature of 1,000 to 1,200 °C and then in a reducing atmosphere at a temperature of 1,200 to 1,350 °C. The same re-oxidation and re-reduction steps as in Example 6 were used to produce a laminated ceramic capacitor with a varistor function. Figure 8 is a flow chart showing this manufacturing process.

The other manufacturing conditions, such as the number of laminated sheets, were identical to those of Examples 1 to 6, and various electrical properties were measured as described therein.

Almost the same electrical properties as in Example 6 were obtained, except that the laminated ceramic capacitor of Example 7 had an improved capacitance as well as an improved effect on withstanding current surge (350 to 500 A) compared with that of Example 6. This is because preheating in a nitrogen atmosphere during the sintering step prevented de-lamination of the capacitor, release of the electrical Prevents loosening of the electrical connections of the inner electrodes and imperfect contact between the inner electrodes and the outer electrodes, as indicated in Example 2.

It was confirmed that when the external electrodes made of the external electrode paste further containing Pd were used in Example 7, the resulting laminated ceramic capacitor with varistor function had lower Tan δ and equivalent series resistance (ESR) as well as improved capacitance and surge resistance effect. It was also confirmed that this effect of the additive could be achieved even in the case where not only Pd was used, but Pt or a mixture of Pd and Pt.

A powdery raw material obtained by dissolving at least one compound containing an atom selected from the group consisting of Li, Na and K in Ni or a Ni-containing compound can be used for internal and external electrode pastes in Examples 5 to 7, as noted in Example 1.

As mentioned in Example 1, a powdery raw material for an external electrode paste prepared by dissolving a combination of at least one compound containing an atom selected from the group consisting of Li, Na and K and at least one compound containing a Pd atom or a Pt atom in Ni or a Ni-containing compound can also be used.

As described in Examples 1 to 7, a laminated ceramic capacitor having a varistor function with Ni internal electrodes has been developed. When Ni, which is a base metal, is used in the internal electrodes, since Ni is oxidized at relatively low temperatures and the external electrodes are easily insulated, it has been proposed that an atom such as Li, Na or K be incorporated in Ni or a Ni-containing compound is dissolved to reduce oxidation by valence control. According to this method, oxidation of the Ni inner electrodes is remarkably reduced and therefore a laminated ceramic capacitor with a varistor function having excellent electrical properties for practical use including reliability and durability can be obtained.

When the outer electrodes containing nickel as the main component and the inner electrodes are used, both the outer electrodes and the inner electrodes contain nickel as the main component, which makes it possible to produce a laminated ceramic capacitor with a varistor function at a low manufacturing cost.

Further, when at least one compound containing a Pd atom or a Pt atom is added to the external electrodes, the electrical characteristics of the laminated ceramic capacitor are improved.

The Ni outer electrodes (i.e., outer electrodes containing Ni as a main component) have a number of advantages in terms of assembling the capacitor and in terms of electrical properties of the capacitor, such as excellent electrical connection to the Ni inner electrodes (i.e., inner electrodes containing Ni as a main component), heat resistance to soft solder, low impedance characteristics, a lower probability of migration, and the like, compared with conventional Ag or Ag-Pd outer electrodes. However, as mentioned in Example 3, when the amount of Li₂CO₃ supplied to the outer electrodes is increased, microcracks may occur in the vicinity of the outer electrodes of the ceramic element due to the difference in shrinkage ratio between the Ni outer electrodes and the ceramic element, which brings about some disadvantages such as inferior electrical properties, low reliability, and a shorter service life. To solve these problems, the following methods have been proposed to reduce the difference in shrinkage ratio:

(1) Adding the same material as that used for the ceramic element to the external electrode paste;

(2) Controlling the particle size and viscosity of the outer electrode paste;

(3) Checking the sintering conditions; and

(4) Checking the thickness of the outer electrode paste after coating.

The methods (1) - (3) are hardly effective and are not fundamental solutions. As for the method (4), when the thickness of the external electrode paste becomes larger than 40 μm, microcracks occur to a noticeable extent. The generation of the microcracks disappears when the coated thickness is made as thin as possible, resulting in the improvement of the electrical characteristics, reliability and life of the laminated ceramic capacitor.

However, when the above method (4) is performed, the external electrodes having a smaller thickness may sometimes cause poorer electrical connections with the internal electrodes, and the tensile load capacity of the external electrodes may sometimes be reduced, making it difficult to perform testing of the laminated semiconductor ceramic capacitor mounted on a substrate.

Therefore, when the thin Ni outer electrodes are covered with additional Ag or Ag-Pd outer electrodes, excellent electrical connections with the inner electrodes and improved tensile load capacity of the outer electrodes can be achieved, eliminating these problems.

The following examples illustrate a manufacturing process using this method.

Example 8

First, 0.1 mol% of Li₂CO₃ powder was added to a NiO powder having an average particle size of 0.5 μm or less and a purity of 90% or higher, and the mixture was calcined in air at a temperature of 1,100 °C for 2 hours. The calcined powder was used as a raw material for internal electrodes, and another calcined powder prepared by adding 1.0 mol% of Li₂CO₃ to NiO was used as a raw material for the external electrodes. The powdery raw materials were dispersed in a solvent together with an organic binder such as a butyral resin compound to form an internal and external electrode paste. Then, as shown in Figure 2, a composition of 97 mol% of SrTiO₃ was prepared. (Sr/Ti=0.97), 0.5 mol% of Nb₂O₅, 0.5 mol% of Ta₂O₅, 1.0 mol% of MnO₂ and 1.0 mol% of SiO₂ were formed into green sheets 1a, 1b and 1c having a thickness of about 30 µm by the doctor blade method, and the green sheets 1b were cut into a predetermined size. Patterns of the internal electrode paste 2 were printed on the green sheets 1b by a screen printing method according to the predetermined size, as shown in Fig. 2. As is clear from Fig. 2, the Ni internal electrode paste 2 was not printed on the uppermost and lowermost green sheets 1a and 1c. The patterns of the internal electrode paste 2 printed on the middle layers of the laminated green sheets 1b reached an edge of the sheets, and the green sheets are stacked in such a manner that the edges reaching the internal electrodes were alternately superimposed and the edges not reaching the internal electrodes were alternately superimposed. The uppermost and lowermost green sheets 1a and 1c were put on the uppermost and lowermost parts (usually, a plurality of green sheets 1b are laminated), and the green sheets 1b having the above internal electrode paste thereon were laminated therebetween. Then, the laminated green sheets 1b were heat-pressed and brought into contact with each other with the uppermost and lowermost green sheets 1a and 1c to form a laminated body. Then, the external electrode paste (i.e., the lower layer of the external electrode paste) containing Ni as a main component was coated to a thickness of about 20 µm on both edges of the laminated body in which terminals of the internal electrode paste 2 were alternately exposed to the opposite ends. The laminated body was then heated at a temperature in the range of 600 to 1,250 ºC in air to remove the binder, thereby calcining the laminated body. The calcined body was sintered by heating at 1,200 to 1,350 ºC in a reducing atmosphere. After sintering, another Ag or Ag-Pd (containing 10 wt% Pd) external electrode paste (i.e., upper layer of external electrode paste) was coated on the external electrodes 3a, and the Ag paste was baked by heating at 600 to 950 °C in air, thereby obtaining a laminated ceramic capacitor 4a with varistor function as shown in Figure 9, which had a plurality of internal electrodes 2a in the ceramic element, the terminals of the internal electrodes 2a alternately reaching their opposite edge of the ceramic element one by one, and the external electrodes 3a were arranged on opposite edges of the ceramic element so that the external electrodes 3a can be electrically connected to the terminals of the internal electrodes 2a alternately exposed to the edges of the element, and further Ag or Ag-Pd external electrodes 3b were arranged on the external electrodes 3a.

The size of the laminated ceramic capacitor with a varistor function, abbreviated as Type 1.3, is 1.60 mm in width, 3.20 mm in length and 1.20 mm in thickness. The capacitor comprises 30 effective sheets on which patterns of the internal electrodes are printed. Figure 10 is a flow chart showing a manufacturing process according to the present invention.

For the laminated ceramic capacitor with varistor function thus produced, the electrical properties such as capacitance, Tan δ, a varistor voltage, a non-linear voltage index α, an equivalent series resistance (ESR) and the effect on surge current withstand capability are shown in Tables 14 and 15.

Each electrical property was obtained under the following experimental conditions. The experimental conditions for preparing the laminated samples were 1,050 ºC, 2 h for binder removal and calcination in air and 1,250 ºC, 2 h for sintering in the reduced atmosphere of N₂:H₂ = 99:1.

* The capacitance C was measured at 1.0 V and 1.0 kHz.

* The varistor voltage V0.1 mA was measured at 0.1 mA.

* The voltage nonlinearity index α was calculated from the values of the varistor voltage measured at 0.1 mA and 1.0 mA, respectively, using the following equation:

α; = 1 / log (V1mA/V0.1mA)

* The equivalent series resistance (ESR) is defined as the resistance at the resonance frequency, measured at 1.0 V.

* The effect of surge current resistance was calculated by measuring the maximum current observed under the conditions that the current wave was 8 x 20 µS and the varistor voltage change V0.1mA changed by 10%. Table 14 Table 15

The samples marked by the symbol * in Tables 14 and 15 are comparative examples. These samples of the semiconductor ceramic elements marked by the symbol * are not sufficiently re-oxidized and short-circuited because the baking temperature of the Ag or Ag-Pd outer electrodes was lower than 800 ºC. Therefore, the electrical characteristics of these elements are not measured. When the baking temperature is increased to a temperature in the range of 800 to 950 ºC, the ceramic element is sufficiently oxidized and the electrical characteristics of a laminated ceramic capacitor with a varistor function can be achieved. Likewise, the laminated ceramic capacitors with Ag outer electrodes have a slightly lower equivalent series resistance (ESR) than those having Ag-Pd outer electrodes because Pd has a slightly higher resistivity than Ag.

It was also confirmed that the surge current withstand effect for the laminated ceramic capacitor was 250 A. When microcracks occur in the ceramic element, the surge current withstand effect is usually reduced to 50 A or lower. For this reason, it is considered that generation of microcracks in the vicinity of the outer electrodes of the ceramic element did not occur.

When examining the inside of the sintered body with a metal microscope, no microcracks were found.

Furthermore, it was confirmed that the electrical connection of the laminated ceramic capacitor obtained in Example 8 and the tensile strength of its external electrodes were sufficient to mount the laminated ceramic capacitor on the substrate.

The external electrodes containing 1.0 mol% Li₂CO₃ were used in Example 8. However, it was confirmed that external electrodes containing less than 1.0% Li₂CO₃ provided the same effect.

It was also confirmed that when Pd was added in addition to the NiO-Li₂CO₃ underlayer outer electrode paste, the resulting ceramic capacitor had a lower Tan δ and a lower equivalent series resistance (ESR). It was observed that a relatively high resistance layer was formed at the boundary between the Ni underlayer outer electrode and the Ag or Ag-Pd overlayer outer electrode when Pd was not added to the underlayer outer electrode paste. On the other hand, it was confirmed that such a resistance layer was not formed when Pd was added to the underlayer outer electrode paste. outer electrode paste because an alloy of Ni and Ag or Ag-Pd is formed by the added Pd. However, this phenomenon was effective only when Pd was added to the lower layer outer electrode paste, but it was not effective even though Pd was added to the upper layer outer electrode paste. Also, Pd or a combination of Pd and Pt provided the same effect.

Example 9

The sintering step of Example 8 was replaced by first heating in a nitrogen atmosphere at an elevated temperature of 1,000 to 1,200 ºC and then in a reduced atmosphere at a temperature of 1,200 to 1,350 ºC. A laminated ceramic capacitor having a varistor function was manufactured by the same method as in Example 8 except for this sintering step. Figure 11 is a flow chart showing this manufacturing process.

The other manufacturing conditions such as the number of laminated sheets were identical to those of Example 8, and various electrical properties were measured as described therein.

Almost the same electrical properties as in Example 8 were obtained, except that the laminated ceramic capacitor of Example 9 had an improved capacitance and an improved effect on withstanding surge current (300 A) compared with that of Example 8. This was because preheating in a nitrogen atmosphere during the sintering step prevented the delamination of the capacitor, the dissolution of the electrical connections of the internal electrodes and the imperfect contact between the internal electrodes and the external electrodes, as stated in Example 2.

It was confirmed that when Pd was added in addition to the outer electrode paste, the resulting laminated ceramic capacitor had a lower Tan δ and equivalent series resistance (ESR) as well as improved capacitance and surge current resistance. Pt or a combination of Pd and Pt also showed the same effect.

Example 10

The sintered body obtained by the same method as in Examples 8 and 9 was re-oxidized at 900 °C for 1 hour in air, re-reduced at 400 °C for 1 hour in a reducing atmosphere of N2:H2 = 99:1, followed by coating the Ni external electrodes (i.e., lower layer external electrodes) with an Ag or Ag-Pd external electrode paste (i.e., upper layer external electrode paste), and then baked at 600 to 950 °C in air to prepare a laminated ceramic capacitor having a varistor function. The electrical characteristics of the laminated ceramic capacitor thus obtained are shown in Tables 16 and 17. Also, Figure 12 shows a flow chart showing the manufacturing process of this example.

The other manufacturing conditions such as the number of laminated sheets were identical to those of Examples 8 and 9, and various electrical properties were measured as described therein. Table 16 Table 17

Almost the same electrical properties as in Examples 8 to 9 were obtained, as shown in Tables 16 and 17.

The electrical properties of the laminated ceramic capacitor with a varistor function of Example 10 are obtained when the baking temperature of the Ag or Ag-Pd outer electrodes is in the range of 600 to 800 ºC, or in the range of 800 to 950 ºC because the re-oxidation step is interposed in Example 10, not as in Examples 8 and 9.

However, if the re-reduction temperature exceeds 700 ºC in a reducing atmosphere after reoxidation, not only the external electrodes but also the ceramic element may be reduced. For this reason, the re-reduction time or the H₂ concentration should be controlled. The optimal re-reduction temperature was in the range of 400 to 600 ºC according to the experimental results.

Furthermore, it was confirmed that the electrical connection of the laminated ceramic capacitor obtained in Example 10 and the tensile strength of its external electrodes were suitable for fixing the laminated ceramic capacitor on the substrate.

It was also confirmed that when Pd was added in addition to the NiO-Li2CO3 outer electrode paste, the resulting laminated ceramic capacitor had a lower Tan δ and a lower equivalent series resistance (ESR). Also, Pt or a combination of Pd and Pt showed the same effect.

Example 11

The sintering step of Example 10 was replaced by first heating in a nitrogen atmosphere at an elevated temperature of 1,000 to 1,200 ºC and then in a reducing atmosphere at a temperature of 1,200 to 1,350 ºC. The sintered ceramic capacitor with a varistor function was manufactured by the same method as in Example 10 except for this sintering step. Figure 13 is a flow chart showing this manufacturing process.

The other manufacturing conditions, such as the number of laminated sheets, were identical to those of Examples 8 to 10, and various electrical properties were measured as described therein.

Almost the same electrical properties as in Examples 8 to 10 were obtained, except that the laminated ceramic capacitor of Example 11 had an improved capacitance and an improved effect on withstanding surge current (300 A) compared with that of Example 10. This is because preheating in a nitrogen atmosphere during the sintering step prevents delamination of the capacitor, loosening of the internal electrodes, and imperfect contact between the internal electrodes and the external electrodes, as mentioned in Example 2.

It was also confirmed that when Pd was added to the underlayer outer electrode paste, the resulting laminated ceramic capacitor had a lower Tan δ and a lower equivalent series resistance (ESR) as well as an improved capacitance and an improved surge current withstand effect. Also, Pt or a combination of Pd and Pt showed the same effect.

Example 12

The sintered body obtained by the same method as in Examples 8 to 11 was re-oxidized at 900 °C for 1 hour in air, followed by coating the external electrodes with an Ag or Ag-Pd external electrode paste, reduced at 400 °C for 1 hour in the reducing atmosphere of N₂:H₂ = 99:1, and then heat-treated at a temperature in the range of 600 to 950 °C for 30 minutes in air to prepare a laminated ceramic capacitor having a varistor function. The electrical characteristics of the laminated ceramic capacitor having a varistor function are shown in Tables 18 and 19. Figure 14 is a flow chart showing the manufacturing process of this example.

The other manufacturing conditions such as the number of laminated sheets were identical to those of Examples 8 to 11, and various electrical properties were measured as described therein. Table 18 Table 19

Almost the same electrical properties as in Examples 8 to 11 were obtained, as shown in Tables 18 and 19.

The process of Example 12 comprises the following steps: coating the sintered body with the Ag or Ag-Pd outer electrode paste immediately after re-oxidation; re-reducing in a reducing atmosphere; and heat treating the body in air. The resulting laminated ceramic capacitor has higher capacitance, varistor voltage product and voltage nonlinearity index than those of Examples 10 and 11. As in Examples 10 and 11, when the re-reduction temperature exceeds 700 ºC in a reducing atmosphere after re-oxidation, not only the outer electrodes but also the ceramic element may be reduced. For this reason, the reduction time or the H₂ concentration should be controlled. According to the experimental results, the optimum re-reduction temperature was in the range of 400 to 600 ºC.

However, it was confirmed that the electrical connection of the laminated ceramic capacitor obtained in this example and the tensile strength of its external electrodes were suitable for fixing the laminated ceramic capacitor on the substrate.

It was also confirmed that when Pd was added to the NiO-Li2CO3 outer electrode paste, the resulting laminated ceramic capacitor had a lower Tan δ and equivalent series resistance (ESR). Also, Pt, or a combination of Pd and Pt showed the same effect.

Example 13

The sintering step of Example 12 was replaced by first heating in a nitrogen atmosphere at an elevated temperature of 1,000 to 1,200 ºC and then in a reducing atmosphere at a temperature of 1,200 to 1,350 ºC. The sintered ceramic capacitor with a varistor function was manufactured by the same method as in Example 12 except for this sintering step. Figure 15 is a flow chart showing this manufacturing process.

The other manufacturing conditions, such as the number of laminated sheets, were identical to those of Examples 8 to 12, and various electrical properties were measured as described therein.

Almost the same electrical properties as in Examples 8 to 12 were obtained, except that the laminated ceramic capacitor of Example 13 had an improved capacitance and an improved effect on withstanding surge current (300 A) compared with that of Example 12. This is because preheating in a nitrogen atmosphere during the sintering step prevents delamination of the capacitor, loosening of the internal electrodes, and imperfect contact between the internal electrodes and the external electrodes, as mentioned in Example 2.

It was also confirmed that when Pd was added to the underlayer outer electrode paste, the resulting laminated ceramic capacitor had a lower Tan δ and a lower equivalent series resistance (ESR) as well as an improved capacitance and an improved surge current withstand effect. Also, Pt or a combination of Pd and Pt showed the same effect.

According to the six different methods of Examples 8 to 13, a laminated ceramic capacitor having a varistor function with satisfactory electrical properties and mechanical strength can be obtained by coating a laminated body with a Ni external electrode paste. In the methods of Examples 8 and 9, the baking step of the Ag or Ag-Pd external electrodes may also be the re-oxidation step of the ceramic element. Therefore, the baking temperature is limited to 800 °C or higher, making it difficult to control the electrical properties of the laminated ceramic capacitor such as capacitance or varistor voltage. However, the resulting laminated ceramic capacitor has constant electrical properties that are very good and good reproducibility for practical uses. On the other hand, since the methods of Examples 10 to 13 involve a re-oxidation step provided in addition to the baking step, the regulation of the re-oxidation temperature and the temperatures in the subsequent steps makes it easier to control the electrical properties. However, there is still a Another aspect of these processes is that it is difficult to control the re-reduction step in a reducing atmosphere after re-oxidation. Also, the electrical properties of the laminated ceramic capacitor in Examples 8 and 9 appear when the baking temperature of the Ag or Ag-Pd outer electrodes reaches 800 ºC, not only because the grain boundaries of the ceramic element are oxidized but because glass flax is contained in the outer electrode paste.

In the processes of Examples 8 to 13, a ceramic capacitor having a varistor function was manufactured by coating a laminated body with a Ni external electrode paste (i.e., external electrode paste containing Ni as a main component). The following Examples 14 to 19 illustrate a process for manufacturing a laminated ceramic capacitor having a varistor function by coating a calcined body in which the binder is removed with a Ni external electrode paste (i.e., external electrode paste containing Ni as a main component).

Example 14

The laminated body obtained by using the internal electrode paste having the same composition and the same internal electrodes as in Examples 8 to 13 was heated to a temperature of 1,050 °C in air, thereby removing the binder and calcining the laminated body. Then, the external electrode paste (i.e., lower layer external electrode paste) was coated to a thickness of 20 µm on both edges of the calcined body in which terminals of the internal electrodes were alternately exposed in opposite directions. The calcined body was sintered at 1,250 °C in the reducing atmosphere of N₂:H₂ = 99:1, followed by coating the external electrodes with an Ag or Ag-Pd external electrode paste (i.e., upper layer external electrode paste) and baked at a temperature in the range of 600 to 950 °C in air. The electrical properties of the laminated ceramic capacitor, thus obtained are shown in Tables 20 and 21. Figure 16 is a flow chart showing the manufacturing process according to this example.

The other manufacturing conditions such as the number of laminated sheets were identical to those of Examples 8 to 13, and various electrical properties were measured as described therein. Table 20 Table 21

The samples marked with the symbol * in Tables 20 and 21 are comparative examples. These sintered semiconductor ceramic elements marked with the symbol * are not sufficiently re-oxidized because the baking temperature of the Ag or Ag-Pd outer electrodes was lower than 800 ºC and short-circuited. When the baking temperature is increased to a temperature in the range of 800 to 950 ºC, the ceramic element is sufficiently re-oxidized and the electrical characteristics of a laminated ceramic capacitor having a varistor function can be obtained. Almost the same electrical characteristics as in Example 8 were obtained. According to the experimental results, the ceramic element heated in air at a low temperature of 800 ºC for binder removal and calcination was fragile with lower mechanical strength and required careful handling. On the other hand, the underlayer outer electrodes laminated on the ceramic element heated to a temperature of over 1,200 ºC for binder removal and calcination tended to peel off after sintering. Therefore, the optimal heating temperature for binder removal and calcination was in the range of 800 to 1,200 ºC.

It was confirmed that the electrical connection of the laminated ceramic capacitor obtained in Example 14 and the tensile strength of its external electrodes were suitable for fixing the laminated ceramic capacitor on the substrate.

Example 15

The sintering step of Example 14 was replaced by first heating in a nitrogen atmosphere at an elevated temperature of 1,000 to 1,200 ºC and then in a reducing atmosphere at a temperature of 1,200 to 1,350 ºC. The sintered ceramic capacitor with a varistor function was manufactured by the same method as in Example 14 except for this sintering step. Figure 17 is a flow chart showing this manufacturing process.

The other manufacturing conditions such as the number of laminated sheets were identical to those of Example 14, and various electrical properties were measured as described therein.

Almost the same electrical properties as in Example 14 were obtained, except that the laminated ceramic capacitor of Example 15 had an improved capacitance and an improved effect on the withstanding of surge current (300 A) compared with that of Example 14. This is because the preheating in a nitrogen atmosphere during the sintering step prevents the delamination of the capacitor, the loosening of the internal electrodes and the imperfect contact between the internal electrodes and the external electrodes, as stated in Example 2.

It was also confirmed that when Pd was added to the underlayer outer electrode paste, the resulting laminated ceramic capacitor had a lower Tan δ and a lower equivalent series resistance (ESR) as well as an improved capacitance and an improved effect on surge current withstand capability. Also, Pt or a combination of Pd and Pt showed the same effect.

Example 16

The sintered body obtained by the same method as in Examples 14 and 15 was re-oxidized at 900 °C for 1 hour in air, re-reduced at 400 °C for 30 minutes in the reducing atmosphere of N₂:H₂ = 99:1, followed by coating the Ni external electrodes with an Ag or Ag-Pd external electrode paste, and then baked at a temperature of 600 to 950 °C in air to prepare a laminated ceramic capacitor having a varistor function. The electrical characteristics of the laminated ceramic capacitor are shown in Tables 22 and 23. Also, Figure 18 is a flow chart showing the manufacturing process of this example.

The other manufacturing conditions, such as the number of laminated sheets, were identical to those of Examples 14 and 15, and various electrical properties were measured as described therein. Table 22 Table 23

Almost the same electrical properties as in Examples 14 and 15 were obtained, as shown in Tables 22 and 23.

The electrical properties of the laminated ceramic capacitor having a varistor function according to Example 16 are obtained when the baking temperature of the Ag or Ag-Pd outer electrodes is in the range of 600 to 800 ºC or in the range is from 800 to 900 ºC because the re-oxidation step is introduced, unlike Examples 14 and 15. However, if the re-reduction temperature exceeds 700 ºC in a reducing atmosphere after reoxidation, not only the external electrodes but also the ceramic element may be reduced. For this reason, the re-reduction time or the H₂ concentration should be controlled. According to the results of the experiments, the optimum re-reduction temperature is in the range of 400 to 600 ºC. The same electrical properties as in Example 10 were also obtained.

It was confirmed that the electrical connection of the laminated ceramic capacitor obtained in this example and the tensile strength of its external electrodes were suitable for fixing the laminated ceramic capacitor on the substrate.

Example 17

The sintering step of Example 16 was replaced by first heating in a nitrogen atmosphere at an elevated temperature of 1,000 to 1,200 ºC and then in a reducing atmosphere at a temperature of 1,200 to 1,350 ºC. The sintered ceramic capacitor with a varistor function was manufactured by the same method as in Example 16 except for this sintering step. Figure 19 is a flow chart showing this manufacturing process.

The other manufacturing conditions, such as the number of laminated sheets, were identical to those of Examples 14 to 16, and various electrical properties were measured as described therein.

Almost the same electrical properties as in Examples 14 to 16 were obtained, except that the laminated ceramic capacitor of Example 17 had an improved capacitance and an improved effect on the withstand surge currents (300 A) compared to that of Example 16. This is because preheating in a nitrogen atmosphere during the sintering step prevents delamination of the capacitor, loosening of the internal electrodes, and imperfect contact between the internal electrodes and the external electrodes, as stated in Example 2.

It was also confirmed that when Pd was added to the underlayer outer electrode paste, the resulting laminated ceramic capacitor had a lower Tan δ and a lower equivalent series resistance (ESR) as well as an improved capacitance and an improved effect on surge current withstand capability. Also, Pt or a combination of Pd and Pt showed the same effect.

Example 18

A sintered body obtained by the same method as in Examples 14 to 17 was re-oxidized at 900 °C for 1 hour in air, followed by coating the Ni external electrodes with an Ag or Ag-Pd external electrode paste, re-reduced at 400 °C for 30 minutes in the reducing atmosphere of N₂:H₂ = 99:1, and then heat-treated at 800 °C for 30 minutes in air to prepare a laminated ceramic capacitor having a varistor function. The electrical characteristics of the laminated ceramic capacitor are shown in Tables 24 and 25. Figure 20 is a flow chart showing the preparation process of this example.

The other manufacturing conditions such as the number of laminated sheets were identical to those of Examples 14 to 17, and various electrical properties were measured as described therein. Table 24 Table 25

Almost the same electrical properties as in Examples 14 to 17 were obtained, as shown in Tables 24 and 25.

The method of Example 18 comprises the steps of coating the sintered body with the Ag or Ag-Pd outer electrode paste immediately after re-oxidation; re-reducing in a reducing atmosphere; and heat treating the body in air. The resulting laminated ceramic capacitor has higher capacitance, varistor voltage product and voltage nonlinearity index than those of Examples 16 and 17. As in Examples 16 and 17, however, if the re-reduction temperature exceeds 700 ºC in a reduced atmosphere after re-oxidation, not only the outer electrode but the ceramic element may be reduced. For this reason, the re-reduction time or the H₂ concentration should be controlled. According to the results of the experiments, the optimum re-reduction temperature was in the range of 400 to 600 ºC. If the same electrical characteristics as in Example 12 were obtained.

It was confirmed that the electrical connection of the laminated ceramic capacitor obtained in Example 18 and the tensile strength of its external electrodes were suitable for fixing the laminated ceramic capacitor on the substrate.

Example 19

The sintering step of Example 18 was replaced by first heating in a nitrogen atmosphere at an elevated temperature of 1,000 to 1,200 ºC and then in a reducing atmosphere at a temperature of 1,200 to 1,350 ºC. The sintered ceramic capacitor with a varistor function was manufactured by the same method as in Example 18 except for this sintering step. Figure 21 is a flow chart showing this manufacturing process.

The other manufacturing conditions, such as the number of laminated sheets, were identical to those of Examples 14 to 18, and various electrical properties were measured as described therein.

Almost the same electrical properties as in Examples 14 to 18 were obtained, except that the laminated ceramic capacitor of Example 19 had an improved capacitance and an improved effect on withstanding surge current (300 A) compared with that of Example 18. This is because preheating in a nitrogen atmosphere during the sintering step prevents delamination of the capacitor, detachment of the inner electrodes, and imperfect contact between the inner electrodes and the outer electrodes, as mentioned in Example 2.

It was also confirmed that when Pd was added to the underlayer outer electrode paste, the resulting laminated ceramic capacitor had a lower Tan δ and a lower equivalent series resistance (ESR) as well as an improved capacitance and an improved effect on surge current withstand capability. Also, Pt or a combination of Pd and Pt showed the same effect.

According to the six different methods used in Examples 14 to 19, a laminated ceramic capacitor having a varistor function with satisfactory electrical properties and mechanical strength can be manufactured by coating a calcined body in which the binder is removed with a Ni external electrode paste. In the methods used in Examples 14 and 15, the baking step of the Ag or Ag-Pd external electrodes may also be the re-oxidation process of the ceramic element. Therefore, the baking temperature is limited to 800 °C or higher, which makes it difficult to control the electrical properties of the laminated ceramic capacitor such as capacitance and varistor voltage. However, the resulting laminated ceramic capacitor has constant electrical properties and good reproducibility for practical uses. On the other hand, because the processes used in Examples 16 to 19 include a re-oxidation step provided in addition to the baking step, the regulation of the re-oxidation temperature and the temperatures in the subsequent steps makes it easy to control the electrical properties. However, there is another aspect of these processes, which is that it is difficult to control the re-reduction step in a reducing atmosphere after the reoxidation. Also, the electrical properties of the laminated Ceramic capacitor in Examples 14 and 15 occurs when the baking temperature of the Ag or Ag-Pd outer electrodes reaches 800 ºC or more, not only because the grain boundaries of the ceramic element are oxidized but because glass flax is contained in the outer electrode paste. Also, almost the same electrical characteristics as in Examples 8 to 13 are obtained in Examples 14 to 19. According to the results of the experiments, the ceramic element heated at a low temperature of less than 800 ºC for binder removal and calcination was fragile with low mechanical strength and required careful handling. On the other hand, the outer electrodes stacked on the ceramic element heated at a temperature of over 1,200 ºC for binder removal and calcination tended to peel off after sintering. Therefore, the optimal temperature for binder removal and calcination was in the range of 800 to 1,200 ºC.

Furthermore, when rounding is introduced to provide a ceramic member having an R-shape at its edge in the manufacture of the laminated ceramic capacitor, it is difficult to round the laminated body in the process of Examples 8 to 13. When the rounding step is carried out, it is easy to round the ceramic member after heating to a temperature in the range of 100 to 200 °C in air to remove the solvent contained therein. In contrast, in the processes of Examples 14 to 19, it is easier to introduce the rounding step because, compared with the previous process, the calcined body in which the binder is removed is rounded. However, it is difficult to round a body heated to a temperature of less than 800 °C to remove the binder and calcine because of low mechanical strength and difficult treatment.

In the processes of Examples 8 to 19, a laminated ceramic capacitor having a varistor function was prepared by coating a laminated body or a calcined body in which the binder is removed, with a Ni outer electrode paste, followed by various manufacturing steps.

The following examples illustrate a method for producing a laminated ceramic capacitor having a varistor function obtained by coating the sintered body with a Ni external electrode paste (external electrode paste containing Ni as a main component) after re-oxidation

Example 20

The laminated body obtained by using an internal electrode paste having the same composition and internal electrodes as in Examples 8 to 19 was calcined at 1,050 °C in air. Then, the calcined body was sintered at 1,250 °C in the reducing atmosphere of N₂:H₂ = 99:1. After sintering, the sintered body was re-oxidized at 900 °C for 1 hour in air, and a Ni external electrode paste was coated to a thickness of 20 µm on both edges of the sintered body with terminals of the internal electrodes alternately exposed to opposite sides. The sintered body was calcined at 650 °C in the reducing atmosphere of N₂:H₂ = 99:1. = 99:1, followed by coating the Ni outer electrodes with an Ag or Ag-Pd outer electrode paste and baking at 600 to 950 ºC in air. The electrical properties of the laminated ceramic capacitor are shown in Tables 26 and 27. Figure 22 is a flow chart showing the manufacturing process of this example.

The other manufacturing conditions such as the number of laminated sheets were identical to those of Examples 8 to 19, and various electrical properties were measured as described therein. Table 26 Table 27

Almost the same electrical properties as Examples 8 to 19 were obtained, as shown in Tables 26 and 27.

The laminated ceramic capacitor with a varistor function according to Example 20 has a low varistor voltage and a low voltage nonlinearity index as compared with those of Examples 8 to 19. This is because the ceramic element is easily reduced when the Ni external electrode paste is baked at an elevated temperature of 650 ºC in a reducing atmosphere. If the baking temperature is lower than 650 ºC, the Ni external electrode paste is not easily sintered. On the other hand, if the baking temperature is 700 ºC , not only the outer electrode but also the ceramic element can be reduced.

It was confirmed that the electrical connection of the laminated ceramic capacitor obtained in Example 20 and the tensile strength of the external electrodes were suitable for fixing the laminated ceramic capacitor on the substrate.

Example 21

The sintering step of Example 20 was replaced by first heating in a nitrogen atmosphere at an elevated temperature of 1,000 to 1,200 ºC and then in a reducing atmosphere at a temperature of 1,200 to 1,350 ºC. The sintered ceramic capacitor with a varistor function was manufactured by the same method as in Example 20 except for this sintering step. Figure 23 is a flow chart showing this manufacturing process.

The other manufacturing conditions, such as the number of laminated sheets, were identical to those of Examples 8 to 20, and various electrical properties were measured as described therein.

Almost the same electrical properties as in Examples 14 to 20 were obtained, except that the laminated ceramic capacitor of Example 21 had an improved capacitance and an improved effect on withstanding surge current (300 A) compared with that of Example 20. This is because preheating in a nitrogen atmosphere during the sintering step prevents delamination of the capacitor, loosening of the internal electrodes, and imperfect contact between the internal electrodes and the external electrodes, as mentioned in Example 2.

It was also confirmed that when Pd was added to the underlayer outer electrode paste, the resulting laminated ceramic capacitor had a lower Tan δ and a lower equivalent series resistance (ESR) as well as an improved capacitance and an improved effect on surge current withstand capability. Also, Pt or a combination of Pd and Pt showed the same effect.

A powdery raw material obtained by dissolving at least one compound containing an atom selected from the group consisting of Li, Na and K in Ni or a compound containing Ni can be used for the internal and external electrode paste in Examples 8 to 21 as shown in Example 1.

Also, a powdery raw material prepared by dissolving a combination of at least one compound containing an atom selected from the group consisting of Li, Na and K and at least one compound containing a Pd atom and a Pt atom in Ni or a Ni-containing compound can be used for the underlayer outer electrode paste as shown in Example 1.

The external electrodes containing 1.0 mol% Li₂CO₃ were used in Examples 9 to 21. However, it was found that the external electrodes containing less than 1.0 mol% Li₂CO₃ showed the same effect.

A laminated ceramic capacitor having a varistor function can be easily manufactured by various manufacturing methods as described in Examples 1 to 21.

A material (composition) of a ceramic capacitor having an intergrain insulated structure will be described below.

A ceramic material containing SrTiO3 as a main component is generally made semiconductive by reducing or sintering in a reducing atmosphere with the addition of a semiconductivity accelerator. However, this method does not necessarily make the ceramic material semiconductive depending on the types of the semiconductivity accelerators. The use of SiTiO3 containing a stoichiometric excess amount of Sr or Ti accelerates the semiconductivity of the ceramic material with the increase of lattice defects in the crystal. Moreover, the addition of at least one element of the group consisting of Nd2O5, Ta2O5, V2O5, W2O5, Dy2O3, Nd2O3, Y2O3, La2O3 accelerates the semiconductivity of the ceramic material. and CeO₂ (hereinafter these compounds are referred to as the first component), making the ceramic materials semiconductive due to valence control.

Both Mn and Si (hereinafter referred to as the second component) are important materials for forming a laminated structure and lack of either of these two components results in the function not being exhibited.

It has been thought that it would be difficult to manufacture a SrTiO3 type laminated ceramic capacitor with a varistor function, for the following reasons.

First of all, a ceramic capacitor material having a varistor function such as SrTiO3 has different functions and properties from an inner electrode material in a sintering step and a re-oxidation step. When the ceramic capacitor material is sintered in a reducing atmosphere, the inner electrode material encloses H2 gas contained in the reducing atmosphere and is expanded in this sintering step because it is made of metal. Also, the inner electrode material can be oxidized to a metal oxide in a re-oxidation step or prevent the ceramic capacitor material from being re-oxidized.

Second, a surface dispersion method becomes necessary for forming a laminated ceramic capacitor having a varistor function, which comprises the steps of sintering the ceramic capacitor material in a reducing atmosphere to make it semiconductive; coating the surface of the ceramic capacitor material with a high-resistivity metal oxide such as MnO2, CuO2, Bi2O3 and Co2O3; and re-oxidizing the resulting material in air so as to disperse the metal oxide in the grain boundaries of the material, resulting in an insulated ceramic body. However, it is technically difficult to disperse the metal oxide into a ceramic element having a laminated structure and alternating internal electrodes.

The inventors of the present invention have discovered the following facts, as described in Japanese Patent Application No. 1-36757.

First, a ceramic capacitor with varistor function was readily prepared by adding the second components as well as the first components to a ceramic material of SrTiO₃ with an excess amount of Ti and sintering the material in a reducing atmosphere followed by a re-oxidation step. Spreading the metal paste with high electrical resistance over the surface of the ceramic plates was found to be unnecessary for forming insulating grain boundaries. The experimental facts are interpreted as follows: The added second components, together with an excess amount of Ti, form a liquid phase with a Mn, Si and Ti ternary oxide system at relatively low temperatures during the sintering step. The liquid phase enhances the sintering of the grains, while the oxides melt and are deposited in the grain boundaries. When the capacitor element in which a liquid phase having Mn, Si and Ti ternary oxide system precipitates in these grain boundaries is re-oxidized in air, the capacitor element is insulated due to the Mn, Si and Ti ternary oxide system precipitating in the grain boundaries, whereby a ceramic capacitor having a varistor function having an intergrain insulated structure can be easily manufactured.

Furthermore, it was found that an excess amount of Ti prevents the oxidation of the internal electrodes as well as the diffusion of metal oxides into the internal electrodes. For this reason, the ceramic material of SrTiO₃ with an excess amount of Ti was used in the present invention.

Second, the SrTiO3 material with an excess amount of Ti to which the second component was added was made semiconductive by sintering in the nitrogen atmosphere as well as in the reducing atmosphere. This fact can be interpreted in part by the same reasoning as in the above discussions that the solid metal oxides are converted to a liquid phase at a relatively low temperature. The added Mn not only forms a liquid phase but also acts as an atomic valence control agent. When Mn acts as an atomic valence control agent, the ionic valence of the Mn ion is +2 or +4, and its electron state is unstable and tends to be activated, thereby enhancing the sinterability. This is the reason why the ceramic material is readily made semiconductive by the sintering step in the nitrogen atmosphere by adding Mn ions as the second component.

Third, the raw materials formed into laminated capacitor sheets were calcined in air before being subjected to the sintering step. This treatment prevented the problems caused in the laminated ceramic capacitor with varistor function, such as the dissolution of electrical connections in the internal electrodes, the delamination of the ceramic sheets, the decrease in sintered density and the non-uniformity of the sintered body. Furthermore, electrical properties such as capacitance, voltage nonlinearity index α and varistor voltage as well as the reliability in the performance of the capacitor were greatly improved.

According to the present invention, in view of the foregoing, a laminated ceramic capacitor having a varistor function can be easily manufactured by Sintering the material of the ceramic capacitor with a varistor function can be produced simultaneously together with the material of the inner electrode.

In the present invention, the Sr/Ti ratio of SrTiO3 is controlled because, if the Sr/Ti ratio is larger than 1.00, the amount of Sr will be in excess of the amount of Ti. Thus, the liquid phase consisting of a ternary oxide system of Mn, Si and Ti is difficult to form, the intergrain insulated structure of the ceramics is difficult to form with the above composition, and furthermore, oxidation and diffusion of the materials of the internal electrodes occur, resulting in poor electrical properties and poor reliability. On the other hand, if the Sr/Ti ratio is smaller than 0.95, the obtained sintered body becomes porous and the sintered density decreases. Powder materials having an average particle size of 0.5 µm or less have been used as the starting material of the laminated ceramic capacitor with varistor function for the following reasons. When a powder having an average particle size of more than 0.5 μm is used, the particles tend to coagulate in the slurry, whereby the surface of the raw sheets formed using a non-uniform slurry becomes rough and smoothness cannot be maintained. The sintering density and the packing density of the obtained sintered body are low, and the sintered body is difficult to make semiconductive, whereby the electrical characteristics of the ceramic capacitor tend to become unstable.

The reason why the total amount of the second components, MnO₂ and SiO₂, added is also controlled is first of all as follows. If the total amount of these components is less than 0.2 mol%, the effect of the added material cannot be obtained. Therefore, the formation of a liquid phase consisting of a ternary oxide system of Mn, Si and Ti becomes difficult, the formation of a grain boundary isolated structure of the ceramic is difficult, and the electrical properties and the sintered density are deteriorated. On the other hand, if the total amount of these components is 5.0 mol%, , the amount of metal oxides with high electrical resistance deposited in the grain boundaries increases and the electrical properties of the ceramic capacitor also deteriorate.

The step of heating the laminated body to remove the binder and calcining it at a temperature of 800 to 1,250 °C is the most important step in the method of forming a laminated ceramic capacitor with a varistor function according to the present invention. Most of the electrical properties and reliability of the produced ceramic capacitor with a varistor function are determined during this step. The purpose of this step is to improve the adhesion between the material of the ceramic portion of the ceramic capacitor with a varistor function and the material of the internal electrodes and to regulate the sintering density, the uniformity in the structure of the sintered body and the average grain size of the crystal particles in the intergrain-insulated semiconductor ceramic material of the laminated ceramic capacitor with a varistor function. The rate of temperature rise was set at 200 ºC/h or less for the debindering and calcining heating steps because slower temperature rises provided more desirable results after the debindering and calcining heating steps.

The heating temperature for binder removal and calcination in air has been limited to the range of 800 to 1,250 ºC. If the temperature is lower than 800 ºC, this step is not effective enough, and if the temperature exceeds 1,250 ºC, the characteristics and reliability of the capacitor deteriorate sharply for the following reasons:

(1) The ceramic capacitor with varistor function is sintered instead of being calcined by heating at this high temperature range. When the capacitor previously sintered in air is subjected to sintering in a reducing atmosphere or in a nitrogen atmosphere, the sintered body shrinks quickly and suffers from concentrated stresses, which causes delamination and cracks in the laminated ceramic capacitor with varistor function.

(2) The oxidation of Ni and the sintering of the ceramic part of the ceramic capacitor with varistor function will proceed at the same time when Ni is used as the material for the inner electrodes. The sintered body reacts with Ni, followed by the diffusion of Ni, resulting in the breakage of the inner electrodes, delamination and the formation of cracks in the laminated ceramic capacitor with varistor function.

(3) When the laminated ceramic body is calcined at a high temperature above 1,250 ºC, oxides containing Mn, Si or Ti contained in the ceramic body form a liquid phase of the ternary oxide. This liquid phase is rapidly sintered together with the ceramic body, so that the growth of the grains of the oxide is accelerated. Accordingly, the sintering density becomes low and the packing density of the oxide into the ceramic grain boundaries is reduced.

(4) The sintered body treated in the above manner is difficult to make semiconductive later during the sintering step in the reducing or nitrogen atmosphere.

The laminated ceramic capacitor with varistor function thus manufactured has a larger capacitance and exhibits much better temperature and frequency characteristics than the laminated varistor disclosed in the above-mentioned Japanese Patent Publication No. 58-23921. The ceramic capacitor according to the present invention is manufactured by laminating ceramic capacitor materials with a varistor function which have both the functions of a normal capacitor which absorbs noise and those of a varistor which absorbs impulses and static electricity, while the above-described prior art varistor is simply made of stacked Varistor materials which exhibit an excellent ability to absorb surge currents. The laminated ceramic capacitor with varistor function according to the present invention is different from that of the prior art in terms of its functions and uses.

Although TiO₂ was added to SrTiO₃ in preparing SrTiO₃ having an excess amount of Ti in the examples of the present invention, other Ti-containing compounds such as carbonates, hydroxides, organic compounds and the like may also be used to provide the same effect.

In the examples, SrTiO₃ was used as the starting material, but the same effect can be achieved by using a combination of SrO or SrCO₃ and TiO₂.

It was confirmed that when Sr(1-x)BaxTiO₃ (where x is in the range of 0 < x ≤ 0.3) is used as the main component of the green sheet instead of SrTiO₃, a laminated ceramic capacitor having a varistor function can be manufactured by using the same inner electrode composition, outer electrode composition and manufacturing method as described above. As described in Japanese Patent Application No. 1-62402, when Sr(1-x)BaxTiO₃ is used with Ba dissolved, the resulting laminated ceramic capacitor has an improved capacitance. The reason why the range of x was defined in Sr(1-x)BaxTiO₃ is that the Curie point of BaTiO₃ occurs when x exceeds 0.3, the capacitance-temperature change rate and the temperature coefficient of varistor voltage become larger, and the capacitor characteristics and varistor characteristics become unstable with respect to temperature. Therefore, the reliability and performance are deteriorated.

It was also confirmed that by using Sr(1-x)BaxTiO₃ (where x is in the range of 0.001 ≤ x < 0 2) as the main component of the green sheet instead of SrTiO₃, a laminated ceramic capacitor with varistor function could be manufactured. can be produced using the same inner electrode composition, outer electrode composition and manufacturing process as described above. As described in Japanese Patent Application No. 1-69651, when Sr(1-x)BaxTiO₃ is used with Ca dissolved, the resulting laminated ceramic capacitor has improved Tan δ and temperature characteristics due to the controlled growth of the crystal grains. The reason why the range of x was defined in Sr(1-x)BaxTiO₃ is that the growth of the crystal grains is not controlled because x is less than 0.001 and the particle size of the crystal is widely distributed, whereby Tan δ and temperature characteristics become poor. If x exceeds 0.2, the resulting laminated ceramic capacitor will have lower capacitance and reduced varistor characteristics due to accelerated oxidation.

As for MnO₂ and SiO₂ as second components, carbonates and hydroxides of these are also effective in preparing the starting material. However, with respect to Mn, it has been found that MnCO₃ is more suitable for preparing a capacitor element having stable properties and good mass-producibility because the particle size distribution of the compound is fine and uniform and the compound is easily pyrolyzed.

In the previous examples, the sintering step was carried out in a reducing atmosphere with the composition N2:H2 = 99:1. When the H2 concentration of the atmosphere is increased, the following phenomena are observed with respect to both the material of the inner electrode and the material of the ceramic capacitor with varistor function.

(1) The electrode material is expanded by enclosing H₂ gas.

(2) The material of the ceramic capacitor with varistor function becomes semiconductive faster.

These phenomena cause problems in the laminated ceramic capacitor with a varistor function in terms of electrical and mechanical properties, such as breakage of electrical connections in the internal electrodes, delamination of the ceramic sheets, formation of cracks in the ceramic sheets, and incomplete re-oxidation of the ceramic material. Therefore, when sintering is carried out in an atmosphere in which the H₂ concentration is increased, it is preferable for producing a ceramic capacitor with desirable properties that the sintering temperature is made somewhat lower (1,200 to 1,300 ºC). On the other hand, a ceramic capacitor with a varistor function is rather difficult to make semiconductive when it is sintered in a reducing atmosphere containing a small amount of H₂ gas. Therefore, the material is preferably sintered in a slightly higher temperature range (1,300 ºC to 1,450 ºC). The concentration ratio of H₂ to N₂ is preferably in the range of 99.5:0.5 to 95.0:5.0.

In the examples described above, a mixed powder was calcined in air. However, it was confirmed that the calcination step when carried out in a nitrogen atmosphere was also advantageous.

Also, the capacitance-temperature change rate and the temperature coefficient of varistor voltage are improved by adding at least one element selected from the group consisting of Na₂SiO₃ and Li₂SiO₃. At least one element selected from the group consisting of Na₂SiO₃ and Li₂SiO₃ acts as a carrier for uniformly diffusing the liquid phase of a ternary oxide system of Mn, Si and Ti in the grain boundaries, forming distinct interfaces between the semiconductor crystal region and a grain boundary region of high resistance. When the amount of at least one element selected from the group consisting of Na₂SiO₃ and Li₂SiO₃ added as a third component is less than 0.05 mol%, the effects of the additive cannot be achieved and little improvement in the capacitance temperature change rate and the temperature coefficient of the varistor voltage are observed. When the amount of the third component added exceeds 2.0 mol%, at least one element selected from the group consisting of Na₂SiO₃ and Li₂SiO₃ serving as a carrier will be in excess in the grain boundaries, thereby decreasing the capacitance and the voltage nonlinearity index α, increasing the equivalent series resistance (ESR), decreasing the sintering density and deteriorating the mechanical strength.

A mixture of SiO₂ and at least one element selected from the group consisting of Na₂O and Li₂O can also be used as the third component instead of at least one element selected from the group consisting of Na₂SiO₃ and Li₂SiO₃. However, when a mixture of Si₂ and at least one element selected from the group consisting of Na₂O and Li₂O is used, it easily decomposes during the sintering step, since at least one element selected from the group consisting of Na₂O and Li₂O is a very unstable compound, and it is prone to decompose or diffuse into the atmosphere, whereby little of at least one element selected from the group consisting of Na atoms and Li atoms remains in the produced sintered body. Moreover, it was confirmed that at least one element selected from the group consisting of Na⁺ and Li⁺ formed by the partial ionization of Na₂O and Li₂O migrates under the high temperature load and the high voltage, bringing about deterioration of the capacitor characteristics. The effects of at least one element selected from the group consisting of added Na ions and Li ions can be advantageously provided by adding the ion in the form of a compound with SiO₂.

It was confirmed that Na ions and Li ions should be added to the material in the form of a compound of at least one element selected from the group consisting of Na₂SiO₃ and Li₂SiO₃.

Furthermore, the addition of the fourth component, Al₂O₃, increases the voltage nonlinearity index α and decreases the equivalent series resistance (ESR) because added Al₂O₃ is dissolved into the crystal lattice and decreases the electrical resistance of the crystal grains. When the amount of Al₂O₃ added as the fourth component is less than 0.05 mol%, the properties of the capacitor are not desirably affected by the additive, resulting in no improvement in the voltage nonlinearity index α and no decrease in the equivalent series resistance (ESR). On the other hand, when the amount added exceeds 2.0 mol%, this amount exceeds the saturation solubility in the crystal lattice. Therefore, an excess amount of Al₂O₃ precipitates. in the grain boundaries, which reduces the electrical resistance of the grain boundaries and thereby greatly reduces the capacitance and the voltage nonlinearity index α.

Also, the capacitance-temperature change rate and the temperature coefficient of varistor voltage are improved by adding at least one element selected from the group consisting of NaAl₂O₃ and LiAl₂O₃ as a variation of the third and fourth components in the same manner as when adding at least one element selected from the group consisting of Na₂SiO₃ and Li₂SiO₃. Na atoms or Li atoms present in at least one element selected from the group consisting of NaAlO₂ and LiAlO₂ act as a carrier for uniformly spreading the liquid phase of a ternary oxide system of Mn, Si and Ti in the grain boundaries, thereby forming distinct interfaces in the semiconductor crystal region and a high-resistivity grain boundary region.

Secondly, the voltage nonlinearity index α is increased and the equivalent series resistance (ESR) is decreased by the addition of at least one element selected from the group consisting of NaAl₂O₃ and LiAl₂O₃, since at least one atom selected from the group consisting of Al and Li present in the added compounds NaAl₂O₃ and LiAl₂O₃. is dissolved into the crystal lattice, thereby reducing the electrical resistance of the crystal grains. When the added amount of at least one element selected from the group consisting of NaAl₂O₃ and LiAl₂O₃ is less than 0.05 mol%, the effects of the additive cannot be achieved and only slight improvements in the capacitance temperature change rate and the temperature coefficient of varistor voltage are observed. Also, the voltage nonlinearity index α is not improved and the equivalent series resistance (ESR) is not reduced. When the added amount of the third component exceeds 4.0 mol%, this amount exceeds the saturation solubility in the crystal lattice. Therefore, at least one element selected from the group consisting of NaAl₂O₃ and LiAl₂O₃ is is deposited in the crystal boundaries and this reduces the electrical resistance of the grain boundaries, thereby lowering the capacitance and the voltage nonlinearity index α, increasing the equivalent series resistance (ESR), reducing the sintered density and deteriorating the mechanical strength.

A mixture of Al₂O₃ and at least one element selected from the group consisting of Na₂O and Li₂O can also be used as the fifth component, instead of at least one element selected from the group consisting of NaAl₂O₃ and LiAl₂O₃. However, when a mixture of Al₂O₃ and at least one element selected from the group consisting of Na₂O and Li₂O is used, it tends to decompose or diffuse into the atmosphere because at least one element selected from the group consisting of Na₂O and Li₂O is a very unstable compound and is easily decomposed during the sintering step, whereby little of the at least one element selected from the group consisting of Na atoms and Li atoms remains in the produced sintered body. Moreover, it was confirmed that at least one element selected from the group consisting of Na+ and Li+ formed by the partial ionization of Na₂O and Li₂O migrates under the load of high temperature and high voltage, which brings about deterioration of the capacitor characteristics. The effects of the at least one element selected from the group consisting of added Na ions and Li ions are advantageously provided by the addition of the ion in the form of NaAlO₂ or LiAlO₂. These compounds are stable in the grain boundaries.

It was confirmed that Na ions and Li ions should be added to the material in the form of a compound consisting of at least one element selected from the group consisting of NaAlO₂ and LiAlO₂.

Although the sintered body was re-oxidized at 900 ºC in air during the re-oxidation step of Examples 3 to 21, it was confirmed that the electrical characteristics appeared when the re-oxidation temperature was changed to a temperature in the range of 900 to 1,250 ºC. Since Ni tends to be oxidized in the re-oxidation in air, the sintered body is preferably re-oxidized in a slightly lower temperature range (900 to 1,050 ºC).

Also, the Ag or Ag-Pd outer electrodes can be baked under a nitrogen atmosphere instead of air, which was used in Examples 8 to 21. However, the material is preferably baked at a slightly higher temperature range (800 to 950 ºC) in a nitrogen atmosphere to provide better electrical properties.

In addition, the mixed powder of NiO and Li₂CO₃ can also be calcined in the other temperature range under a nitrogen atmosphere instead of 1,100 ºC in air to give the same effect. However, it was confirmed that when the mixed powder is not calcined, the laminated ceramic capacitor had a slightly less profound effect on the electrical properties, reliability, durability and mass production capability.

Although according to the above examples at least one compound containing an atom selected from the group consisting of Li, Na and K and at least one compound containing a Pd atom or a Pt atom is dissolved in Ni or a Ni-containing compound, it was confirmed that the same effect can be achieved if only at least one compound containing a Pd atom or a Pt atom is dissolved in Ni or a Ni-containing compound without adding at least one compound containing an atom selected from the group consisting of Li, Na and K.

The capacitor element thus obtained exhibits the following advantages: high capacitance and high voltage nonlinearity index α; low varistor voltage and low equivalent series resistance (ESR); and excellent temperature, frequency and noise characteristics; whereby the capacitor element absorbs low voltage noise and high frequency noise with the function of a conventional capacitor, absorbs high voltage pulses and static electricity with the function of a varistor, and quickly responds to intrusion of abnormal voltage such as noise, pulses and static electricity. The capacitor is expected to replace various applications of conventional capacitors such as film capacitors, laminated ceramic capacitors and semiconductor capacitors. Furthermore, laminated ceramic capacitors with varistor function according to the present invention are smaller in size, higher in capacitance and higher in performance compared with conventional single plate type ceramic capacitors with varistor function, thus also being expected to have a wide range of applications as mounting parts. Furthermore, the laminated ceramic capacitor according to the present invention uses inexpensive Ni for the internal electrodes, so that the raw material cost of this capacitor is expected to be lower compared with the laminated ceramic capacitor with varistor function which uses noble metals such as Pd and Ag as the internal electrodes.

As described above, according to the present invention, a laminated ceramic capacitor with varistor function can be obtained which has both the functions of a capacitor and a varistor. The capacitor works as a conventional capacitor that absorbs low voltage noise and high frequency noise, while it works as a varistor when high voltage pulses and static electricity are generated by surrounding electronic equipment. Therefore, this capacitor can protect semiconductors and electronic equipment from abnormal voltages such as noise, pulses and static electricity generated in the electronic equipment. Practical applications of the capacitor are as follows:

(1) The capacitor can replace conventional film, laminated ceramic and semiconductor ceramic capacitors, which are used as bypass capacitors to protect ICs and LSIs used in electronic equipment.

(2) The capacitor can replace ZnO type capacitors, which are used to prevent destruction and malfunction of electronic equipment caused by static electricity and to absorb ON-OFF surges caused by inductive loads.

The capacitor has both functions described in points (1) and (2) above and a wide range of applications is expected.

A laminated ceramic capacitor with a varistor function according to the present invention, which has Ni internal electrodes, can be easily manufactured according to the invention, since the improvement of both the oxidation resistance of the Ni internal electrodes and the oxidation of the crystal boundaries of the ceramic element would be possible for the following reasons. First, the oxidation rate of Ni, which produces a p-type oxide, is reduced by dissolving a compound containing an atom selected from the group consisting of Li, Na and K in Ni or in a Ni-containing compound, thereby improving the oxidation resistance of Ni. Second, an atom selected from the group consisting of of Li, Na and K, is readily dispersed into the crystal grain boundaries of a ceramic element in a re-oxidation step, acts as an oxygen carrier and accelerates the oxidation of the crystal grain boundaries. The present invention provides these main advantages in the manufacturing process of the capacitors.

Since the laminated ceramic capacitor with varistor function according to the present invention is smaller in size, higher in capacitance and better in performance as compared with conventional single plate type ceramic capacitors with varistor function, the capacitor of the present invention is expected to have a wide range of applications as a highly integrated mounting member for electronic equipment such as video cameras and communication devices.

Accordingly, according to the present invention, capacitor elements having the functions of protecting semiconductors and electronic equipment from the intrusion of abnormal voltages such as noise, impulses and static electricity can be obtained. The characteristics of the capacitor are so stable against temperature changes that the effects of the present invention are greatly improved in terms of practical applications.

Claims (29)

1. A laminated semiconductor ceramic capacitor with intergrain insulation comprising a semiconductor ceramic block having an intergrain insulation structure, a plurality of Ni internal electrodes (2a) and external electrodes (3), the Ni internal electrodes (2a) being arranged in a substantially parallel manner in the ceramic block so as to reach the respective opposite edges of the ceramic block alternately one after another, and the external electrodes (3) being respectively electrically connected to the respective edges of the internal electrodes (2a), characterized in that the Ni internal electrodes (2a) are obtained from a paste containing a powder prepared by dissolving 0.05 mol% to 2.0 mol% of at least one compound containing an atom selected from the group containing Li, Na and K in Ni or a Ni-containing compound having a purity of 90% or higher. 2. A laminated semiconductor ceramic capacitor with intergrain insulation according to claim 1, wherein the external electrodes are made of at least one metal selected from the group consisting of Pd, Ag, Cu, Zn and Ni; their alloys or their mixtures. 3. A laminated semiconductor ceramic capacitor with intergrain insulation according to claim 1, wherein the external electrodes are obtained by dissolving at least one compound containing an atom selected from the group consisting of Li, Na and K; or a combination of at least one compound containing an atom selected from the group consisting of Li, Na and K with at least one compound containing a Pd atom or a Pt atom into Ni or a compound containing Ni. 4. The intergrain insulation type laminated semiconductor ceramic capacitor according to claim 1, wherein the external electrodes comprise: (1) lower external electrodes obtained by dissolving at least one compound containing an atom selected from the group consisting of Li, Na and K, or a combination of at least one compound containing an atom selected from the group consisting of Li, Na and K with at least one compound containing a Pd atom or a Pt atom in Ni or a compound containing Ni, and (2) upper external electrodes of Ag or Ag-Pd type. 5. A laminated semiconductor ceramic capacitor with intergrain insulation according to claim 1, wherein the external electrodes are obtained by dissolving at least one compound containing a Pd atom or a Pt atom in Ni or a Ni-containing compound. 6. A laminated semiconductor ceramic capacitor with intergrain insulation according to claim 1, wherein the external electrodes comprise: (1) lower external electrodes formed by dissolving at least one compound containing a Pd atom or a Pt atom, in Ni or a Ni-containing compound, and (2) upper external electrodes of Ag or Ag-Pd type. 7. The intergrain-insulated laminated semiconductor ceramic capacitor according to claim 1, wherein the intergrain-insulated semiconductor ceramic has as a main component SrTiO₃ with an excess amount of Ti so as to produce a molar ratio of Sr to Ti in the range of 0.95 ≤ Sr/Ti < 1.00; at least one compound selected from the group consisting of Nb₂O₅, Ta₂O₅, V₂O₅, W₂O₅, Dy₂O₃, Nd₂O₃, Y₂O₃, La₂O₃ and CeO₂ in the range of 0.05 to 2.0 mol%; and a combination of at least one compound containing a Mn atom with at least one compound containing a Si atom, the total amount of the combination being in the range of 0.2 to 5.0 mol%, respectively, in terms of MnO₂ and SiO₂. 8. The intergrain-insulated laminated semiconductor ceramic capacitor according to claim 1, wherein the intergrain-insulated semiconductor ceramic has as a main component SrTiO₃ with an excess amount of Ti to produce a molar ratio of Sr to Ti in the range of 0.95 ≤ Sr/Ti < 1.00, at least one compound selected from the group consisting of Nb₂O₅, Ta₂O₅, V₂O₅, W₂O₅, Dy₂O₃, Nd₂O₃, Y₂O₃, La₂O₃ and CeO₂ in the range of 0.05 to 2.0 mol%; at least one compound containing a Mn atom or a Si atom in the range of 0.2 to 5.0 mol% as regards MnO₂ or SiO₂; and at least one compound selected from the group consisting of Na₂SiO₃ and Li₂SiO₃ in the range of 0.05 to 2.0 mol%. 9. The intergrain insulated laminated semiconductor ceramic capacitor according to claim 1, wherein the intergrain insulated semiconductor ceramic comprises, as a main component, SrTiO₃ with an excess amount of Ti to produce a molar ratio of Sr to Ti in the range of 0.95 ≤ Sr/Ti <1.00; at least one compound selected from the group consisting of Nb₂O₅, Ta₂O₅, V₂O₅, W₂O₅, Dy₂O₃, Nd₂O₃, Y₂O₃, La₂O₃ and CeO₂ in the range of 0.05 to 2.0 mol%; at least one compound containing a Mn atom or a Si atom in the range of 0.2 to 5.0 mol% as regards MnO₂ or SiO₂; at least one compound selected from the group consisting of Na₂SiO₃ and Li₂SiO₃ in the range of 0.05 to 2.0 mol%; and Al₂O₃ in the range of 0.05 to 2.0 mol%. 10. The intergrain-insulated laminated semiconductor ceramic capacitor according to claim 1, wherein the intergrain-insulated semiconductor ceramic has as a main component SrTiO₃ with an excess amount of Ti so as to produce a molar ratio of Sr to Ti in the range of 0 95 ≤ Sr/Ti < 1.00, at least one compound selected from the group consisting of Nb₂O₅, Ta₂O₅, V₂O₅, W₂O₅, Dy₂O₃, Nd₂O₃, Y₂O₃, La₂O₃ and CeO₂. in the range of 0.05 to 2.0 mol%, at least one compound containing a Mn atom or a Si atom in the range of 0.2 to 5.0 mol% as regards MnO₂ or SiO₂; and at least one compound selected from the group consisting of NaAlO₂ and LiAlO₂ in the range of 0.05 to 4.0 mol%. 11. The intergrain-insulated laminated semiconductor ceramic capacitor according to claim 1, wherein the intergrain-insulated semiconductor ceramic has as a main component Sr(1-x)BaxTiO₃ (where 0 < x ≤ 0.3) with an excess amount of Ti so as to produce a molar ratio of Sr(1-x)Bax to Ti in the range of 0.95 ≤ Sr(1-x)Bax/Ti < 1.00; at least one compound selected from the group consisting of Nb₂O₅, Ta₂O₅, V₂O₅, W₂O₅, Dy₂O₃, Nd₂O₃, Y₂O₃, La₂O₃ and CeO₂ in the range of 0.05 to 2.0 mol%; and at least one compound containing a Mn atom or a Si atom in the range of 0.2 to 5.0 mol% as regards MnO₂ or SiO₂. 12. Laminated semiconductor ceramic capacitor with intergrain insulation according to Claim 1, wherein the intergrain insulated semiconductor ceramic comprises as a main component Sr(1-x)BaxTiO₃ (where 0 < x ≤ 0.3) with an excess amount of Ti to produce a molar ratio of Sr(1-x)Bax to Ti in the range of 0.95 ≤ Sr(1-x)Bax/Ti <1.00; at least one compound selected from the group consisting of Nb₂O₅, Ta₂O₅, V₂O₅, W₂O₅, Dy₂O₃, Nd₂O₃, Y₂O₃, La₂O₃ and CeO₂ in the range of 0.05 to 2.0 mol%; at least one compound containing a Mn atom or a Si atom in the range of 0.2 to 5.0 mol% as regards MnO₂ or SiO₂; and at least one compound selected from the group consisting of Na₂SiO₃ and Li₂SiO₃ in the range of 0.05 to 2.0 mol%. 13. A laminated semiconductor ceramic capacitor with intergrain insulation according to claim 1, wherein the intergrain insulated semiconductor ceramic has as a main component Sr(1-x)BaxTiO₃ (where 0 < x ≤ 0.3) with an excess amount of Ti so as to produce a molar ratio of Sr(1-x)Bax to Ti in the range of 0.95 ≤ Sr(1-x)Ba/Ti < 1.00; at least one compound selected from the group consisting of Nb₂O₅, Ta₂O₅, V₂O₅, W₂O₅, Dy₂O₃, Nd₂O₃, Y₂O₃, La₂O₃ and CeO₂ in the range of 0.05 to 2.0 mol%; at least one compound containing a Mn atom or a Si atom in the range of 0.2 to 5.0 mol% as regards MnO₂ or SiO₂; at least one compound selected from the group consisting of Na₂SiO₃ and Li₂SiO₃ in the range of 0.05 to 2.0 mol%; and Al₂O₃ in the range of 0.05 to 2.0 mol%. 14. A laminated semiconductor ceramic capacitor with intergrain insulation according to claim 1, wherein the intergrain insulated semiconductor ceramic has as a main component Sr(1-x)BaxTiO₃. (where 0 < x (0.3) with an excess amount of Ti so as to produce a molar ratio of Sr(1-x)Bax to Ti in the range of 0.95 ? Sr(1-x)Bax/Ti <1.00; at least one compound selected from the group consisting of Nb₂O₅, Ta₂O₅, V₂O₅, W₂O₅, Dy₂O₃, Nd₂O₃, Y₂O₃, La₂O₃ and CeO₂ in the range of 0.05 to 2.0 mol%; at least one compound containing a Mn atom or a Si atom in the range of 0.2 to 5.0 mol% which is MnO₂ or SiO2; and at least one compound selected from the group consisting of NaAlO₂ and LiAlO₂ in the range of 0.05 to 4.0 mol%. 15. A laminated semiconductor ceramic capacitor with intergrain insulation according to claim 1, wherein the intergrain insulated semiconductor ceramic has as a main component Sr(1-x)BaxTiO₃ (where 0.001 ≤ x ≤ 0.2) with an excess amount of Ti so as to produce a molar ratio of Sr(1-x)Bax to Ti in the range of 0.95 ≤ Sr(1-x)Bax/Ti < 1.00; at least one compound selected from the group consisting of Nb₂O₅, Ta₂O₅, V₂O₅, W₂O₅, Dy₂O₃, Nd₂O₃, Y₂O₃, La₂O₃ and and CeO₂, in the range of 0.05 to 2.0 mol%; and at least one compound containing a Mn atom or a Si atom, in the range of 0.2 to 5.0 mol% as regards MnO₂ or SiO₂. 16. A laminated semiconductor ceramic capacitor with intergrain insulation according to claim 1, wherein the intergrain insulated semiconductor ceramic has as a main component Sr(1-x)BaxTiO₃ (where 0.001 ≤ x ≤ 0.2) with an excess amount of Ti so as to produce a molar ratio of Sr(1-x)Bax to Ti in the range of 0.95 ≤ Sr(1-x)Bax/Ti < 1.00; at least one compound selected from the group consisting of Nb₂O₅, Ta₂O₅, V₂O₅, W₂O₅, Dy₂O₃, Nd₂O₃, Y₂O₃, La₂O₃ and and CeO₂, in the range of 0.05 to 2.0 mol%; at least one compound containing a Mn atom or a Si atom, in the range of 0.2 to 5.0 mol% as regards MnO₂ or SiO₂; and at least one compound selected from the group consisting of Na₂SiO₃ and Li₂SiO₃, in the range of 0.05 to 2.0 mol%. 17. The intergrain insulated laminated semiconductor ceramic capacitor according to claim 1, wherein the intergrain insulated semiconductor ceramic has as a main component Sr(1-x)BaxTiO₃ (where 0.001 ≤ x ≤ 0.2) with an excess amount of Ti so as to produce a molar ratio of Sr(1-x)Bax to Ti in the range of 0.95 ≤ Sr(1-x)Bax <1.00; at least one compound selected from the group consisting of Nb₂O₅, Ta₂O₅, V₂O₅, W₂O₅, Dy₂O₃, Nd₂O₃, Y₂O₃, La₂O₃ and CeO₂. in the range of 0.05 to 2.0 mol%; at least one compound which is a Mn atom or Si atom, in the range of 0.2 to 5.0 mol% as regards MnO₂ or SiO₂; at least one compound selected from the group consisting of Na₂SiO₃ and Li₂SiO₃, in the range of 0.05 to 2.0 mol%; and Al₂O₃ in the range of 0.05 to 2.0 mol%. 18. A laminated semiconductor ceramic capacitor with intergrain insulation according to claim 1, wherein the intergrain insulated semiconductor ceramic has as a main component Sr(1-x)BaxTiO₃ (where 0.001 ≤ x ≤ 0 2) with an excess amount of Ti so as to produce a molar ratio of Sr(1-x)Bax to Ti in the range of 0.95 ≤ Sr(1-x)Bax/Ti < 1.00; at least one compound selected from the group consisting of Nb₂O₅, Ta₂O₅, V₂O₅, W₂O₅, Dy₂O₃, Nd₂O₃, Y₂O₃, La₂O₃ and and CeO₂, in the range of 0.05 to 2.0 mol%; at least one compound containing a Mn atom or a Si atom, in the range of 0.2 to 5.0 mol% as regards MnO₂ or SiO₂; and at least one compound selected from the group consisting of NaAlO₂ and LiAlO₂, in the range of 0.05 to 4.0 mol%. 19. A method for producing a laminated semiconductor ceramic capacitor (4) with intergrain insulation, comprising the following steps: a) calcining a mixed powder of a ceramic composition to form an intergrain-isolated structure in air or in a nitrogen atmosphere, b) forming raw sheet structures (1b) by dispersing the calcined powder in a solvent with an organic binder and forming the dispersed powder, wherein the calcined powder is finely ground before dispersing and after calcining, c) forming an internal electrode pattern by applying an internal electrode paste (2) to a surface of each of the green sheets (1b), except for the uppermost and lowermost sheets (1a, 1c), whereby terminals of the internal electrodes (2a) are extended to alternatively reach the corresponding opposite edges of the green sheets (1b) one after the other, d) laminating and compressing the raw sheet structures (1b) with the internal electrode pattern with the uppermost and lowermost raw sheet structures (1a, 1c), e) calcining the resulting raw sheet (1b) in air at a temperature of not more than 1250 ºC, f) sintering the calcined sheet structures (1b) in a reducing atmosphere, whereby a sintered ceramic body with internal electrodes (2a) is formed, g) reoxidizing the sintered ceramic body in air, h) covering the edges of the sintered ceramic sheet structures (1b) with an external electrode paste, whereby the connections of the internal electrodes (2a) are exposed towards these edges, and i) firing the paste to form external electrodes (3) so that the internal electrodes (2a) are electrically connected to the external electrodes (3), characterized in that j) for the internal electrode paste (2), a mixed powder is prepared which contains Ni or a Ni-containing compound with a purity of 90% or higher and 0.05 mol% to 2.5 mol% of at least one compound containing an atom selected from the group containing Li, Na and K, k) the mixed powder is calcined in air or in a nitrogen atmosphere to dissolve the compound containing an atom selected from the group consisting of Li, Na and K in the Ni or the Ni-containing compound, l) the calcined mixed powder is finely ground and mixed in a solvent with an organic binder, thereby forming an internal electrode paste (2), m) the temperature of the calcination step (e) is at least 800 ºC, and n) in the reoxidation step (g), the atom selected from the group consisting of Li, Na and K is dispersed into the crystal grain boundaries of the ceramic element of the ceramic body. 20. A method for producing a laminated semiconductor ceramic capacitor (4) with intergrain insulation, comprising the following steps: a) calcining a mixed powder of a ceramic composition to form an intergrain isolated structure in air or in a nitrogen atmosphere, b) forming raw sheet structures (1b) by dispersing the calcined powder in a solvent with an organic binder and forming the dispersed powder, wherein the calcined powder is finely ground before dispersing and after calcining, c) forming an internal electrode pattern by applying an internal electrode paste (2) to a surface of each of the green sheets (1b), except for the uppermost and lowermost sheets (1a, 1c), whereby terminals of the internal electrodes (2a) are extended to alternatively reach the corresponding opposite edges of the green sheets (1b) one after the other, d) laminating and compressing the raw sheet structures (1b) with the internal electrode pattern with the uppermost and lowermost raw sheet structures (1a, 1c), e) covering the edges of the raw surface structures (1b) with external electrode paste, whereby connections of the internal electrodes (2a) are exposed towards the edges, characterized in that f) the resulting green sheet structures (1b) are calcined in air at a temperature in the range of 800 to 1250 ºC, g) the calcined sheet structures (1b) are sintered in a reducing atmosphere, whereby a sintered ceramic body with inner and outer electrodes (2a, 3) is formed, h) the sintered ceramic body is reoxidized in air, whereby the atom selected from the group consisting of Li, Na and K can disperse into the crystal grain boundaries of a ceramic element of the ceramic body, and i) the outer electrodes (3) are re-reduced, and j) for the internal electrode paste (2), a mixed powder is prepared which contains Ni or a Ni-containing compound with a purity of 90% or more and 0.05 mol% to 2 mol% of at least one compound containing an atom selected from the group consisting of Li, Na and K , k) the mixed powder is calcined in air or in a nitrogen atmosphere to dissolve the compound containing an atom selected from the group consisting of Li, Na and K into the Ni or Ni-containing compound, and l) the calcined mixed powder is finely ground and mixed in a solvent with an organic binder, thereby forming an internal electrode paste (2). 21. A method for producing a laminated semiconductor ceramic capacitor (4) with intergrain insulation, comprising the following steps: a) calcining a mixed powder of a ceramic composition to form an intergrain isolated structure in air or in a nitrogen atmosphere, b) forming raw sheet structures (1b) by dispersing the calcined powder in a solvent with an organic binder and forming the dispersed powder, wherein the calcined powder is finely ground before dispersing and after calcining, c) forming an internal electrode pattern by applying an internal electrode paste (2) to a surface of each of the green sheets (1b), except for the uppermost and lowermost sheets (1a, 1c), whereby terminals of the internal electrodes (2a) are extended to alternatively reach the corresponding opposite edges of the green sheets (1b) one after the other, d) laminating and compressing the raw sheet structures (1b) with the internal electrode pattern with the uppermost and lowermost raw sheet structures (1a, 1c), e) calcining the resulting green sheet (1b) in air at a temperature of not more than 1250 ºC, and f) covering the edges of the calcined ceramic sheet structures (1b) with an external electrode paste, whereby connections of the internal electrodes (2a) are exposed towards these edges, characterized in that g) the temperature of the calcination step (e) is at least 800 ºC, h) the calcined sheet structures (1b) are sintered in a reducing atmosphere, whereby a sintered ceramic body with inner and outer electrodes (2a, 3) is formed, i) the sintered ceramic body is reoxidized in air, whereby the atom selected from the group consisting of Li, Na and K can disperse into the crystal grain boundaries of a ceramic element of the ceramic body, and j) the outer electrodes (3) are re-reduced, and k) for the internal electrode paste (2), a mixed powder is prepared which contains Ni or a Ni-containing compound with a purity of 90% or higher and 0.05 mol% to 2.0 mol% of at least one compound containing an atom selected from the group consisting of Li, Na and K , l) the mixed powder is calcined in air or in a nitrogen atmosphere, so that the compound containing an atom selected from the group consisting of Li, Na and K is dissolved into the Ni or Ni-containing compound, and m) the calcined mixed powder is finely ground and mixed with an organic binder in a solvent, thereby forming an internal electrode paste (2). 22. A method for producing a laminated semiconductor ceramic capacitor (4) with intergrain insulation, comprising the following steps: a) Calcining a mixed powder of a ceramic composition to Formation of an intergrain isolated structure in air or in a nitrogen atmosphere, b) forming raw sheet structures (1b) by dispersing the calcined powder in a solvent with an organic binder and forming the dispersed powder, wherein the calcined powder is finely ground before dispersing and after calcining, c) forming an internal electrode pattern by applying an internal electrode paste (2) to a surface of each of the green sheets (1b), except for the uppermost and lowermost sheets (1a, 1c), whereby terminals of the internal electrodes (2a) are extended to alternatively reach the corresponding opposite edges of the green sheets (1b) one after the other, d) laminating and compressing the raw sheet structures (1b) with the internal electrode pattern with the uppermost and lowermost raw sheet structures (1a, 1c), characterized in that e) the edges of the raw sheet structures (1b) are covered with an underlayer external electrode paste, whereby the connections of the internal electrodes (2a) are exposed towards the edges, f) the resulting green sheet structures (1b) are calcined in air at a temperature in the range of 800 to 1250 ºC, g) the calcined sheet structures (1b) are sintered in a reducing atmosphere, whereby a sintered ceramic body with internal electrodes (2) and underlayer external electrodes is formed, h) a top layer external electrode paste containing Ag or a mixture of Ag and Pd is applied to the bottom layer external electrodes, and i) the upper layer electrode paste is fired in air or in a nitrogen atmosphere to form upper layer external electrodes on the lower layer external electrodes, and wherein j) for the internal electrode paste (2) a mixed powder is prepared which contains Ni or a Ni-containing compound with a purity of 90 % or higher and 0.05 mol% to 2.0 mol% of at least one compound containing an atom selected from the group consisting of Li, Na and K, k) the mixed powder is calcined in air or in a nitrogen atmosphere to dissolve the compound containing an atom selected from the group consisting of Li, Na and K into the Ni or a Ni-containing compound, and l) the calcined mixed powder is finely ground and mixed in a solvent with an organic binder, thereby forming an internal electrode paste (2). 23. A method according to claim 22, characterized in that the underlayer external electrode paste contains Ni; by reoxidizing the ceramic body in air; and re-reducing the external electrodes (3). 24. A method for producing a laminated semiconductor ceramic capacitor (4) with intergrain insulation, comprising the following steps: a) calcining a mixed powder of a ceramic composition to form an intergrain isolated structure in air or in a nitrogen atmosphere, b) forming raw sheet structures (1b) by dispersing the calcined powder in a solvent with an organic binder and forming the dispersed powder, wherein the calcined powder is finely ground before dispersing and after calcining, c) forming an internal electrode pattern by applying an internal electrode paste (2) to a surface of each of the green sheets (1b), except for the uppermost and lowermost sheets (1a, 1c), whereby terminals of the internal electrodes (2a) are extended to alternatively reach the corresponding opposite edges of the green sheets (1b) one after the other, d) Laminating and compressing the raw sheet (1b) with the Internal electrode pattern with the top and bottom raw surface structures (1a, 1c), characterized in that e) the edges of the raw sheet structures (1b) are covered with a underlayer external electrode paste, whereby connections of the internal electrodes (2a) are exposed towards the edges, f) the resulting raw sheet structures (1b) are calcined in air at a temperature in the range of 800 to 1250 ºC, g) the calcined sheet structures (1b) are sintered in a reducing atmosphere, h) the sintered sheets are reoxidized in air, whereby the atom selected from the group consisting of Li, Na and K can disperse into the crystal grain boundaries of a ceramic element of the ceramic body, i) a top layer external electrode paste containing Ag or a mixture of Ag and Pd is applied to the bottom layer external electrodes, j) the resulting fabrics are re-reduced, and k) the re-reduced sheets are heat treated in air to form top layer external electrodes on the bottom layer external electrodes, and wherein l) for the internal electrode paste (2), a mixed powder is prepared which contains Ni or a Ni-containing compound with a purity of 90% or higher and 0.05 mol% to 2.0 mol% of at least one compound containing an atom formed from the group consisting of Li, Na and K , (m) the mixed powder is calcined in air or in a nitrogen atmosphere to dissolve the compound containing an atom selected from the group consisting of Li, Na and K into the Ni or the Ni-containing compound, and n) the calcined mixed powder is finely ground and mixed in a solvent with an organic binder, thereby forming an internal electrode paste (2) is created. 25. A method for producing a laminated semiconductor ceramic capacitor (4) with intergrain insulation, comprising the following steps: a) calcining a mixed powder of a ceramic composition to form an intergrain-isolated structure in air or in a nitrogen atmosphere, b) forming raw sheet structures (1b) by dispersing the calcined powder in a solvent with an organic binder and forming the dispersed powder, wherein the calcined powder is finely ground before dispersing and after calcining, c) forming an internal electrode pattern by applying an internal electrode paste (2) to a surface of each of the green sheets (1b), except for the uppermost and lowermost sheets (1a, 1c), whereby terminals of the internal electrodes (2a) are extended to alternatively reach the corresponding opposite edges of the green sheets (1b) one after the other, d) laminating and compressing the raw sheet (1b) with the internal electrode pattern with the uppermost and lowermost raw sheet (1a, 1c), and e) calcining the resulting raw sheet (1b) in air at a temperature of not more than 1250 ºC, characterized in that f) the temperature of the calcination step (e) is at least 800 ºC, g) the edges of the calcined ceramic sheet structures (1b) are covered with an underlayer external electrode paste, whereby connections of the internal electrodes (2a) are exposed towards the edges, h) the calcined sheet structures (1b) are sintered in a reducing atmosphere, i) a top layer external electrode paste containing Ag or a mixture of Ag and Pd is applied to the bottom layer external electrodes, and j) the upper layer electrode paste is fired in air or a nitrogen atmosphere to form upper layer external electrodes on the lower layer external electrodes, and wherein k) for the internal electrode paste (2), a mixed powder is prepared which contains Ni or a Ni-containing compound with a purity of 90% or higher and 0.05 mol% to 2.0 mol% of at least one compound containing an atom selected from the group consisting of Li, Na and K , (l) the mixed powder is calcined in air or a nitrogen-containing atmosphere to dissolve the compound containing an atom selected from the group consisting of Li, Na and K into the Ni or the Ni-containing compound, and m) the calcined mixed powder is finely ground and mixed in a solvent, whereby an internal electrode paste (2) is formed. 26. Method according to claim 25, characterized in that the sintering of step (h) is followed by re-oxidizing the sintered ceramic body in air and re-reducing the external electrodes (3). 27. A method according to claim 25, characterized in that the sintering of step (h) is followed by re-oxidizing the sintered ceramic body in air, step (i) is followed by re-reducing the sintered and re-oxidized ceramic body, and the sintered, re-oxidized and re-reduced ceramic body is heat-treated in air. 28. A method for producing a laminated semiconductor ceramic capacitor (4) with intergrain insulation, comprising the following steps: a) calcining a mixed powder of a ceramic composition to form an intergrain isolated structure in air or in a nitrogen atmosphere, b) forming raw sheet structures (1b) by dispersing the calcined Powders in a solvent with an organic binder and forming the dispersed powder, whereby the calcined powder is finely ground before dispersion and after calcination, c) forming an internal electrode pattern by applying an internal electrode paste (2) to a surface of each of the green sheets (1b), except for the uppermost and lowermost sheets (1a, 1c), whereby terminals of the internal electrodes (2a) are extended to alternatively reach the corresponding opposite edges of the green sheets (1b) one after the other, d) laminating and compressing the raw sheet structures (1b) with the internal electrode pattern with the uppermost and lowermost raw sheet structures (1a, 1c), e) calcining the resulting raw sheet (1b) in air at a temperature of not more than 1250 ºC, f) sintering the calcined sheet structures (1b) in a reducing atmosphere, thereby producing a sintered ceramic body, g) Re-oxidizing the sintered ceramic body in air, characterized in that h) the temperature of the calcination step (e) is at least 800 ºC, i) in the re-oxidation step (g), the atom selected from the group consisting of Li, Na and K is dispersed into the crystal grain boundaries of the ceramic element of the ceramic body, j) the re-oxidation is followed by covering the edges of the sintered ceramic body with an underlayer external electrode paste, whereby connections of the internal electrodes (2a) are exposed towards the edges, k) the undercoat outer electrode paste is fired in a reducing or nitrogen atmosphere, l) a top layer external electrode paste containing Ag or a mixture of Ag and Pd is applied to the bottom layer external electrodes, and m) the upper layer outer electrode paste is fired in air or a nitrogen atmosphere to form upper layer outer electrodes on the lower layer external electrodes, and n) for the internal electrode paste, a mixed powder is prepared which contains Ni or a Ni-containing compound with a purity of 90% or more and 0.05 mol% to 2.0 mol% of at least one compound containing an atom selected from the group consisting of Li, Na and K, (o) the mixed powder is calcined in air or in a nitrogen atmosphere to dissolve the compound containing an atom selected from the group consisting of Li, Na and K into the Ni or the Ni-containing compound, and p) the calcined mixed powder is finely ground and mixed in a solvent with an organic binder, whereby an internal electrode paste (2) is formed. 29. Process according to one of the preceding process claims, characterized in that the temperature of the calcined sheet-like structures (1b) is raised to a temperature in the range of 1000 to 1200 ºC in a nitrogen atmosphere before sintering.