JPH11150037A - Laminated ceramic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a laminated ceramic capacitor with more layers of internal electrodes and dielectrics to secure high capacitance so that higher dielectric breakdown voltage and electrostriction breakdown generation voltage ensure prevention of crack of capacitor elements caused by mechanical stress. SOLUTION: In addition to multiple layers of capacitors 10, 10a and 10b and outermost dielectric layers 11a and 11b constituting the external surface, layers this capacitor element has middle dielectric layers 12, 12a and 12b between the capacitor layers 10, 10a and 10b. The middle dielectric layers 12, 12a and 12b are thicker than dielectric layers 1b of the capacitor layers 10, 10a and 10b (t1 <t2 ).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer ceramic capacitor having a large capacity and a high withstand voltage laminated structure used for a high voltage circuit or the like.

[0002]

2. Description of the Related Art Generally, in a multilayer ceramic capacitor, an internal electrode is printed on the surface of a ceramic green sheet serving as a dielectric layer, and a plurality of these are laminated to form a capacitor layer and an outer surface layer. A capacitor element is formed by superposing and sintering the outer dielectric layers together, and furthermore, a pair of external electrodes electrically connected to the internal electrodes of the capacitor layer are provided at both ends of the capacitor element. I have.

[0003] The multilayer ceramic capacitor tends to increase the number of internal electrodes and dielectric layers due to a demand for large capacity. However, a dielectric material having a high dielectric constant based on barium titanate or the like has a dielectric constant (ε) of 1,000 to 1,000.
Since it has a crystal structure that is as high as 20,000 and easily forms a dipole, has a large strain and expands and contracts, a piezoelectric phenomenon or a reverse phenomenon in which a voltage is mechanically changed with the application of a voltage is applied. A piezoelectric phenomenon, that is, an electrostrictive phenomenon is likely to occur.

For this reason, in a multilayer ceramic capacitor, if the number of internal electrodes and dielectric layers is simply increased, the expansion and expansion of the capacitor before the dielectric breakdown voltage range is reached due to the electrostriction phenomenon.
By the repetition of contraction, cracks are generated in the capacitor element due to mechanical stress destruction, and the withstand voltage level such as the dielectric breakdown voltage or the electrostriction breakdown generation voltage is lowered. In order to prevent the occurrence of cracks, the dielectric layer of the capacitor layer may be formed to be thick. However, this not only increases the overall shape but also causes a decrease in capacitance due to the thick dielectric layer. Become.

Conventionally, cracks are prevented from being generated in a capacitor element due to the influence of thermal stress due to soldering.
Alternatively, since a reduction in insulation resistance or a short circuit caused by the movement of the electrode material due to the moisture invading from the surface layer and the DC voltage between the electrodes is prevented, a pair of intermediate members are separated and electrically connected to the external electrode. It has been proposed that an electrode is provided on the same surface of a dielectric layer, and that the dielectric layer is interposed between the outermost dielectric layer and the capacitor layer to constitute a capacitor element (Japanese Patent Laid-Open No. 1-242020, Japanese Patent Application Laid-Open No. Hei. Kaihei 5-6695
No. 1).

Further, since voltage breakdown is prevented from occurring between the folded tip of the external electrode and the tip of the internal electrode, the electric field strength is reduced, and the withstand voltage is improved. A dielectric layer in which a pair of electrodes separated and electrically connected to an external electrode are provided on the same surface is arranged on the outermost dielectric layer side, and an external electrode is provided between the dielectric layer and the capacitor layer. It has also been proposed to form a capacitor element with a dielectric layer provided with a floating electrode not connected (Japanese Utility Model Application Laid-Open No. 60-99522).

However, simply adding the above-described dielectric layer prevents the occurrence of cracks in the capacitor element due to mechanical stress destruction due to the electrostriction phenomenon caused by increasing the number of internal electrodes and dielectric layers. It cannot be surely prevented.

[0008]

SUMMARY OF THE INVENTION According to the present invention, a high capacitance value is ensured by increasing the number of internal electrodes and dielectric layers, and a dielectric breakdown voltage and an electrostriction breakdown occurrence voltage are increased.
An object of the present invention is to provide a multilayer ceramic capacitor capable of reliably preventing a crack due to mechanical stress breakdown from occurring in a capacitor element.

It is another object of the present invention to provide a multilayer ceramic capacitor capable of increasing a creeping discharge generation voltage as well as a dielectric breakdown voltage and an electrostriction breakdown generation voltage.

[0010]

In the multilayer ceramic capacitor according to the first aspect of the present invention, in addition to a plurality of capacitor layers and an outermost dielectric layer forming an outer surface layer,
A capacitor element is constituted by interposing an intermediate dielectric layer thicker than the dielectric layer of the capacitor layer between the capacitor layers.

In a multilayer ceramic capacitor according to a second aspect of the present invention, a first capacitor in which a plurality of capacitor layers and an intermediate dielectric layer thicker than the dielectric layer of the capacitor layer are alternately stacked. A second layer in which a capacitor layer, an internal electrode having an opposing area relatively smaller than the internal electrode of the first capacitor layer, and a dielectric layer are alternately overlapped;
A capacitor element is formed by superimposing a second capacitor layer outside the first capacitor layer and further superposing an outermost dielectric layer outside the second capacitor layer. I have.

In the multilayer ceramic capacitor according to a third aspect of the present invention, a dielectric layer having a pair of electrodes separated on the middle and electrically connected to an external electrode provided on the same surface is used as a surface discharge control layer, A capacitor element is formed by interposing the surface discharge control layer between the outermost dielectric layer and the capacitor layer.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the accompanying drawings, the illustrated multilayer ceramic capacitor has an internal electrode 1a.
And the dielectric layers 1b are alternately stacked, and the outermost dielectric layers 11a and 11b forming the outer surface layers, and the dielectric layers forming the respective capacitor layers 10 are formed. body layer 1b ... thick thickness t ₂ than the thickness t ₁ of the (t ₁ <t ₂₎ the intermediate dielectric layer 12 ... the capacitor layer 1
0 and a pair of external electrodes 2 and 3 electrically connected to the internal electrodes 1 a of the capacitor layers 10 are provided at both ends of the capacitor element 1. Have.

[0014] Capacitor layer 10 ... are mainly composed of ceramic dielectric powder of barium titanate, it give a slurry prepared by adding the required organic solvent and a binder, having a predetermined thickness t ₁ by a doctor blade method from the slurry dielectric Obtaining ceramic green sheets to be the body layers 1b, and further printing a predetermined pattern of internal electrodes 1a on the sheet surface of the ceramic green sheets by screen printing from a Pd electrode paste, and laminating a plurality of the ceramic green sheets. Is formed. The thickness t _{1 of the} dielectric layers 1 b is set to about 25 μm in the illustrated embodiment.

The outermost dielectric layers 11a and 11b can be formed by a doctor blade method using a slurry of the same material as the dielectric layers 1b of the capacitor layers 10. Its thickness t
₃ is usually set to about 150 to 300 μm, and is set to about 150 μm in the illustrated embodiment. The intermediate dielectric layers 12 are formed by a doctor blade method using a slurry of the same material as the dielectric layers 1b of the capacitor layers 10 like the outermost dielectric layers 11a and 11b, and have a thickness t _2. It is set to about 50 to 300 μm, and in the illustrated embodiment, to about 50 μm.

As will be described later, each of these layers has a plurality of capacitor layers and an intermediate dielectric layer interposed between the respective capacitor layers, which are alternately superposed on each other, and further, the outermost dielectric layer is provided outside the capacitor layer. After being laminated and press-formed as a dielectric laminated sheet, it is cut into a predetermined component unit, and is subjected to a binder removal step and a firing step to form the capacitor element 1. The capacitor element 1 is formed as a multilayer ceramic capacitor by printing and baking a frit-containing silver-palladium alloy on the end face and applying nickel and tin plating by electroplating to provide external electrodes 2 and 3. Have been.

FIG. 1 shows that the internal electrodes 1a have a thickness t ₁ : 25.
A capacitor layer is formed by laminating 20 dielectric layers 1b of .mu.m and laminating 20 layers.
1 shows a first embodiment having three a and 10b. In this multilayer ceramic capacitor, the intermediate dielectric layers 12, 12a having a thickness t _{2 of} 50 μm are formed on the capacitor layers 10 and 10a.
a, superimposed between each of 10a and 10b, and furthermore, the thickness t
₃ : constituted by superposing outermost dielectric layers 11a and 11b of 150 μm outside capacitor layers 10 and 10b.

FIG. 2 shows that the internal electrodes 1a have a thickness t ₁ : 25.
A capacitor layer is formed by laminating 12 layers on the dielectric layers 1b of.
A second embodiment having five d's is shown. In this multilayer ceramic capacitor, as in the first embodiment, the intermediate dielectric layers 12 to 12c having a thickness t _{2 of} 50 μm are formed with the capacitor layers 10 and 10a, 10a and 10b, 10b and 10c,
Interposed between each of 10c and 10d, thickness t ₃ : 150 μ
m of the outermost dielectric layers 11a and 11b
The capacitor element 1 is formed by superimposing on the outside of 10d.

FIG. 3 shows a third embodiment. In this multilayer ceramic capacitor, as in the second embodiment, the internal electrodes 1a are formed by forming a dielectric layer 1b having a thickness t _{1 of} 25 μm.
... form a capacitor layer by 12 layers stacked is provided on, the capacitor layer 10~10d with 5 comprising a capacitor layer 10 of the intermediate dielectric layer 12~12c thickness t ₂ is 50 [mu] m 10a, and 10a A first capacitor layer is interposed between each of 10b, 10b and 10c, 10c and 10d. In addition to this, the second capacitor layer 1
0e and 10f are superimposed on the outside of the first middle capacitor layers 10 and 10d.

The second capacitor layers 10e, 10f
The internal electrodes 1a similarly to the capacitor layer 10~10d of the in one '... the thickness t _1: 25 [mu] m of the dielectric layer 1b' is formed by 12 layers stacked is provided on .... Also, the internal electrodes 1a 'of the capacitor layers 10e and 10f are formed.
.., The facing area w ₁ is the first capacitor layer 10-1.
Relatively smaller than the internal electrodes 1a ... facing area w ₂ of 0d (w ₁ <w ₂₎ are provided. Outside the second capacitor layers 10e and 10f, the thickness t ₃ : 150 μm
m of the outermost dielectric layers 11a and 11b
The capacitor element 1 is formed by superimposing on the outside of 10d.

FIG. 4 shows a fourth embodiment. In addition to the embodiment shown in FIG. 3, a creeping discharge control layer 13a,
13b constitutes the capacitor element 1. The creeping discharge control layers 13a and 13b are provided with a pair of electrodes 1a ₁ and 1a ₂ that are separated from the middle G and electrically connected to the external electrodes 2 and 3 on the same surface of the dielectric layer 1b ″. This dielectric layer 1b ″ is also made to have a thickness t by a doctor blade method using a slurry of the same material as the other dielectric layers.
₄ : formed to a thickness of 25 μm. The creeping discharge control layers 13a and 13b constitute the capacitor element 1 interposed between the outermost dielectric layers 11a and 11b and the second capacitor layers 10e and 10f.

FIG. 5 shows a multilayer ceramic capacitor having a conventional structure, which is shown as a comparative example of FIGS. In the multilayer ceramic capacitor, the internal electrodes 1a have a thickness of 25 μm.
The capacitor layer 10 is formed by providing the dielectric layers 1b and laminating 60 layers, and the thickness for forming the outer surface layer: 1
The outermost dielectric layers 11a and 11b of 50 μm are superposed on each other to form the capacitor element 1, and a pair of external electrodes 2 electrically connected to the internal electrodes 1a.
3 is provided at both ends of the capacitor element 1.

Fifty samples were prepared for each of the above-described first to fourth embodiments and the conventional example. The generated voltage was measured. This measurement measures 1
The voltage was applied in the insulating oil at a boosting rate of 00 V / sec, and the point where the leakage current reached 10 mA was determined as the breakdown occurrence voltage. The average value is as shown in Table 1, and when an intermediate dielectric layer having a thickness of about 50 μm is provided, even if the thickness of the outermost dielectric layer is suppressed to about 150 μm, compared to a case where no intermediate dielectric layer is provided, Both the dielectric breakdown voltage and the electrostriction breakdown generation voltage can be increased. In particular, when about four layers are provided as in the second embodiment, the electrostriction breakdown generation voltage is 1.
It turns out that it can improve 5 times.

[0024]

[Table 1]

In addition, based on the second and third embodiments, the dielectric breakdown voltage and the electrostriction breakdown occurrence voltage were measured with and without the second capacitor layer. This measurement also uses a voltage of 100V
Applied in an insulating oil at a pressure increase rate of 1 / sec.
The test was performed by determining the point where the current became 0 mA as the breakdown occurrence voltage. The average value is as shown in Table 2. When the second capacitor layer having a relatively small capacity is provided on the outer layer side, both the dielectric breakdown voltage and the electrostriction breakdown generation voltage can be further increased. It can be seen that the strain breakdown generation voltage can be improved by 0.5 KV.

[0026]

[Table 2]

Further, based on the third and fourth embodiments, the creeping discharge generation voltage was measured depending on the presence or absence of the creeping discharge control layer. This measurement was performed by applying a voltage in the air at a boosting rate of 100 V / sec, and judging that the leakage current was 1 mA as the creeping discharge generation voltage. The average value is as shown in Table 3. The polarities of the pair of electrodes where the middle of the creeping discharge control layer is separated and the external electrode are equal, and the lines of electric force do not concentrate between the external electrode and each electrode. As a result, it is found that the generation of the creeping discharge can be suppressed, and the creeping discharge generation voltage can be more than doubled as compared with the case without the creeping discharge control layer.

[0028]

[Table 3]

[0029]

As described above, according to the multilayer ceramic capacitor of the first aspect of the present invention, since the capacitor element is provided with the intermediate dielectric layer, the thickness of the outermost dielectric layer is reduced. However, both the dielectric breakdown voltage and the electrostriction breakdown occurrence voltage can be increased as compared with those having no intermediate dielectric layer, and in particular, the electrostriction breakdown occurrence voltage can be significantly improved.

According to the multilayer ceramic capacitor of the present invention, the second capacitor layer having a relatively small capacitance is provided together with the first capacitor layer alternately stacked with the capacitor layer and the intermediate dielectric layer. Is provided on the outer layer side to constitute the capacitor element, thereby further increasing both the dielectric breakdown voltage and the electrostriction breakdown occurrence voltage, and in particular, the electrostriction breakdown occurrence voltage can be improved.

According to the multilayer ceramic capacitor according to the third aspect of the present invention, since the capacitor element is provided with the creeping discharge control layer together with the capacitor layer alternately superimposed on the intermediate dielectric layer, the dielectric breakdown occurs. Not only can the voltage and electrostriction breakdown occurrence voltage be increased, but the electric field lines do not concentrate between the pair of electrodes separated from the middle of the creeping discharge control layer and the external electrode, so that the creeping discharge control layer is not provided. The creeping discharge generation voltage can be significantly improved as compared with the case.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a multilayer ceramic capacitor including two intermediate dielectric layers according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram illustrating a multilayer ceramic capacitor including four intermediate dielectric layers according to a second embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a multilayer ceramic capacitor including a first capacitor layer and a second capacitor layer according to a third embodiment of the present invention.

FIG. 4 is an explanatory view showing a multilayer ceramic capacitor including a creeping discharge control layer according to a fourth embodiment of the present invention.

FIG. 5 is an explanatory view showing a multilayer ceramic capacitor according to a conventional example by electrode patterns of internal electrodes.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Capacitor element 1a ... Internal electrode 1b ... Dielectric layer 10, 10a, 10b Capacitor layer 11a, 11b Outer dielectric layer 12, 12a, 12c Intermediate dielectric layer 2, 3 External electrode

Claims (3)

[Claims] A capacitor layer in which an internal electrode and a dielectric layer are alternately superposed on each other, and a pair of external electrodes electrically connected to the internal electrode of the capacitor layer are provided at both ends of the capacitor element. A multilayer ceramic capacitor comprising: a plurality of capacitor layers; an outermost dielectric layer forming an outer surface layer; and an intermediate dielectric layer thicker than the dielectric layer of the capacitor layer. A multilayer ceramic capacitor characterized by comprising a capacitor element interposed therebetween. 2. A first capacitor layer in which a plurality of capacitor layers and an intermediate dielectric layer thicker than the dielectric layer of the capacitor layer are alternately stacked, and an internal electrode of the first capacitor layer. A second capacitor layer in which an internal electrode having a relatively smaller opposing area and a dielectric layer are alternately superimposed, the second capacitor layer being superimposed on the outside of the first capacitor layer, And the outermost dielectric layer as the second
The multilayer ceramic capacitor according to claim 1, wherein a capacitor element is formed by superimposing the capacitor element on the outside of the capacitor layer. 3. A creeping discharge control layer comprising a dielectric layer having a pair of electrodes separated on the middle and electrically connected to an external electrode provided on the same surface, and the creeping discharge control layer is defined as an outermost dielectric layer. 3. The multilayer ceramic capacitor according to claim 1, wherein the capacitor element is formed by being interposed between the capacitor layers.