JPH09148175A - Ceramic capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance a ceramic capacitor in mechanical strength without influencing it in electrical properties as a dielectric ceramic. SOLUTION: This ceramic capacitor is formed through such a manner that dielectric layers 2 mainly formed of barium titanate (BaTiO3 ) and inner electrode layers 3 are alternately laminated for the formation of a laminated ceramic capacitor 4, outer layers 7 and 8 formed of material composed of compound mainly consisting of barium titanate (BaTiO3 ) and 40 to 90% by weight of stabilized zirconia are provided to the upside 5 and underside 6 of the ceramic capacitor 4 respectively, and a terminal electrode 9 is provided to each edge face of the ceramic capacitor 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high dielectric constant type ceramic capacitor applied to an electronic circuit board, an electronic component or the like used in a consumer or industrial electronic device, and in particular to various vehicle-mounted control devices. Is a ceramic capacitor suitable for electronic parts such as resonators, capacitors, LC filters and the like.

[0002]

2. Description of the Related Art Conventionally, various dielectric ceramics have been widely used as a dielectric material in electronic circuit boards, electronic parts and the like. As a dielectric ceramic composition having a high dielectric constant, barium titanate (BaTiO ₃ ) is used. The thing mainly made of has been used frequently.

In recent years, with the development and popularization of various vehicle equipment such as car stereos, airbags, fuel injection devices, etc., which are mounted on vehicles, computerization of these control devices has progressed, and development of electronic circuit boards and electronic components for vehicles. The dielectric ceramics have come to be actively used.

However, the high-dielectric-constant dielectric ceramic composition mainly composed of barium titanate (BaTiO ₃ ) as described above has a high dielectric constant and has excellent characteristics as a dielectric ceramic, but it is mechanical. Has low mechanical strength, is easily cracked or chipped due to handling, heating / cooling during mounting work, various external stresses, etc., resulting in deterioration of various electrical characteristics as a dielectric and poor reliability. .

Furthermore, in the case of the above-mentioned vehicle-mounted type, it is necessary to have sufficient mechanical strength and heat resistance due to vibration and high heat generated by the engine. As a recent tendency, in order to reduce the weight of the vehicle and downsize the vehicle-mounted parts. The installation of the above-mentioned various control devices in the engine room is being considered, and the environment of electronic components for vehicles has become more and more severe, and improvement in mechanical strength has been required.

Therefore, in order to solve such a problem, the raw material powder may be made finer, or additives such as metal oxides may be added to improve the mechanical strength of the high dielectric constant type dielectric ceramic composition. It has been proposed (see JP-A-5-279117 and JP-A-6-96987).

[0007]

However, since the final composition does not change in the method of refining the raw material powder to densify the structure, the electrical characteristics such as the dielectric constant of the dielectric ceramic are maintained, but Strength is 18 at 3-point bending strength
The method is as small as 0 MPa or less, and the method of using the metal oxide as an additive has a large possibility of delicately affecting the electrical characteristics of the material itself, and also has a mechanical strength of 120.
The effect of improving the strength was small at about MPa, and the above-mentioned strict requirements were not satisfied.

[0008]

DISCLOSURE OF THE INVENTION The present invention has been made to solve the above problems, and its purpose is to provide a high dielectric constant porcelain with sufficient mechanical properties without affecting electrical characteristics. It is an object of the present invention to provide a ceramic capacitor and its dielectric material that can improve strength.

[0009]

In order to achieve the above-mentioned object, the present inventors have found that barium titanate (Ba) which is the main component is used.
TiO ₃ ), which has a higher mechanical strength than that of barium titanate (BaTiO ₃ ), and a coefficient of thermal expansion similar to that of barium titanate (BaTiO ₃ ).
(iO ₃ ) is a high-strength dielectric material contained in a dielectric composition, and the outer surface layer is formed by sandwiching at least the upper and lower surfaces of a multilayer capacitor having low mechanical strength, thereby providing electrical characteristics. It has been found that the mechanical strength is significantly improved without giving an adverse effect on the strength.

[0010] Ceramic capacitors of the present invention, at least the upper and lower surfaces of the stacked capacitor dielectric layers and internal electrode layers mainly composed of barium titanate (BaTiO ₃₎ are laminated alternately, barium titanate (BaTiO ₃ )
40 to 90% by weight of yttria-stabilized zirconia (YSZ), magnesia-stabilized zirconia (hereinafter referred to as MSZ), or calcia-stabilized zirconia (hereinafter referred to as CSZ) in a dielectric composition whose main component is It is preferable that the outer surface layer of the above-mentioned dielectric is integrated, and it is more preferable that the content of the stabilized zirconia in the outer surface layer is 50 to 75% by weight. Mol% yttria stabilized zirconia (8
Most preferred is YSZ).

The content of the stabilized zirconia is 4
When the amount is less than 0% by weight, the mechanical strength is comparable to that of the conventional example and the effect of improving the strength is not observed, and when the amount exceeds 90% by weight, the bonding force with the dielectric layer is weak and the outer surface layer is It peels off.

Therefore, the content of the above-mentioned stabilized zirconia is specified to be 40 to 90% by weight, and 50 to 75% by weight is most preferable from the viewpoint of improvement of mechanical strength and adhesion to the dielectric layer.

Further, in general, zirconia (ZrO ₂ ) undergoes a large volume change and breaks during transformation, and therefore stabilizers such as calcia (CaO), magnesia (MgO) and yttria (Y ₂ O ₃ ) are used. It is used as a stabilized zirconia that is made into a solid solution to form a cubic or tetragonal crystal phase. Among them, yttria-stabilized zirconia (YSZ)
Has a relatively high Young's modulus and is most suitable for increasing strength.

The yttria-stabilized zirconia (YSZ) has a thermal expansion coefficient of 9.0 to 11.0 × 10 ^-6 /
C., and the coefficient of thermal expansion of a multilayer capacitor containing barium titanate (BaTiO ₃ ) as a main component is about 10.8 × 10.
^Since it is relatively close to ⁻⁶ / ° C., it is possible to avoid the occurrence of cracks and peeling due to the difference in thermal expansion.
Yttria-stabilized zirconia (hereinafter referred to as 3YSZ)
Has a thermal expansion coefficient of about 9.0 × 10 ^-6 / ° C.
Since the coefficient of thermal expansion is about 10.4 × 10 ⁻⁶ / ° C., 8 mol% yttria-stabilized zirconia (8YSZ) is most desirable from the viewpoint of consistency of coefficient of thermal expansion.

[0015]

In the ceramic capacitor of the present invention, the barium titanate () is formed on at least the upper and lower outer surfaces of the laminated capacitor in which the dielectric layers mainly containing barium titanate (BaTiO ₃ ) and the internal electrode layers are alternately laminated. BaTiO ₃ )
Stabilized zirconia is added to the dielectric composition containing 40
Since the layer containing ˜90 wt% is formed, the outer surface layer is present in close contact so as to cover the laminated capacitor part in which the internal electrode exists, and the electric characteristics as a dielectric are not directly affected. The high strength layer reinforces the most stressed outer surface to improve the mechanical strength.

[0016]

DETAILED DESCRIPTION OF THE INVENTION The ceramic capacitor of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of the ceramic capacitor of the present invention.
Main component on the upper surface 5 and lower surface 6 of the multilayer capacitor 4 obtained by stacking dielectric layers 2 and internal electrode layers 3 composed mainly of barium titanate (BaTiO ₃₎ alternately, each barium titanate (BaTiO ₃₎ The outer surface layers 7 and 8 containing 40 to 90% by weight of stabilized zirconia in the dielectric composition
Are integrally formed, and the terminal electrodes 9 are adhered and formed on both ends of the ceramic capacitor.

In the ceramic capacitor 1, a kneaded material of a dielectric powder containing barium titanate (BaTiO ₃ ) as a main component and an organic binder is formed into a sheet shape, and then an internal electrode is adhered to the surface of the dielectric sheet. Stack multiple objects,
Barium titanate (BaTiO 3) containing a predetermined amount of stabilized zirconia without forming internal electrodes on its upper and lower surfaces.
₃ ) A dielectric sheet that is a main component of the outer surface layer is laminated, pressure-bonded, heated to remove the binder, and subsequently baked at a predetermined temperature to be integrated, and then the terminal electrode 9 is Ag.
-Pd paste or the like is applied and baked, or is formed by plating or the like.

[0018]

EXAMPLES Next, the ceramic capacitors of the present invention were evaluated based on the following examples.

First, the dielectric has a temperature coefficient of capacitance of
<± 15% in the temperature range of -55 ° C and + 125 ° C E
As a high dielectric constant material satisfying the IA standard X7R characteristics, 100 parts by weight of barium titanate (BaTiO ₃ ) is added to niobium oxide (Nb) as an additive as shown in Table 1.
₂ O ₅ ), barium carbonate (BaCO ₃ ), manganese oxide (MnO) in a total amount of 1 to 5 parts by weight, and silica (SiO ₂ ) and alumina (Al ₂ O ₃ ) as a sintering aid in a total amount of 0.1 to 5 parts by weight.
0.5 parts by weight was added and mixed with a solvent, an organic binder, and a dispersant in a ball mill for 24 hours to prepare a slurry.

Next, the slurry is formed into a sheet by a doctor blade method to obtain a green sheet having a thickness of 20 μm, and a conductive paste containing silver as a main component is printed on the green sheet to form internal electrodes. A conductive paste layer for forming was formed.

On the other hand, various kinds of stabilized zirconia using yttria, magnesia, and calcia as stabilizers are mixed with a high dielectric constant material having the same composition as the above dielectric so as to have the composition shown in Table 1, and the same as above. A solvent, an organic binder, and a dispersant were added to the mixture, and the mixture was ball-milled for 24 hours to prepare a slurry, which was then formed into a sheet by the doctor blade method to produce a green sheet having a thickness of 20 μm.

[0022]

[Table 1]

Ten to fifteen dielectric green sheets having the conductive paste layer thus obtained are laminated, and one green sheet containing the above-mentioned stabilized zirconia is laminated on each of the upper and lower surfaces thereof and sandwiched, and then 80 2 while heating to ℃
It was pressurized at a pressure of 00 kg / cm ² and thermocompression bonded. Then, the binder is removed while heating, and subsequently 1300 ° C to 1400 ° C.
The temperature was raised to a temperature of ° C, and the temperature was maintained for 2 hours for firing and integration.

Then, an electrode material containing silver as a main component is applied to both end faces of the sintered body, and the mixture is exposed to about 800 in the air.
Baking at a temperature of ℃, to form a terminal electrode electrically connected to the internal electrode, width 1.6mm, length 3.2m
A ceramic capacitor for evaluation having a thickness of m and a thickness of 1.2 mm was produced.

Prior to conducting a three-point bending strength test using the thus-obtained ceramic capacitor for evaluation, an automatic bridge type measuring device was used, and 1 kHz between the terminal electrodes, 1
Vrms voltage is applied, permittivity ε, dielectric loss tan
δ was measured, and then the rate of change in capacitance TCC (%) at −55 ° C. and + 125 ° C. was measured.

Then, the bending strength by three-point bending was measured using the sample whose dielectric properties were evaluated.

[0027]

[Table 2]

As is apparent from Table 2, Sample No. 2 having a stabilized zirconia content of more than 90% by weight has poor adhesion between the laminated capacitor portion and the outer surface layer and is peeled from the interface to contribute to the improvement of strength. Sample Nos. 14 and 15 each having a content of less than 35% by weight have a lower bending strength than Sample No. 1 of the conventional example, whereas all of the samples of the present invention have electrical characteristics. Maintains the same value as the comparative example, and the bending strength is 175M of the conventional example.
Since it exceeds Pa, the effect of improving the strength is remarkably recognized.

The present invention is not limited to the above-described embodiments.

[0030]

As described above, according to the ceramic capacitor of the present invention, at least upper and lower surfaces of a multilayer capacitor in which dielectric layers containing barium titanate (BaTiO ₃ ) as a main component and internal electrode layers are alternately laminated. 40 to a dielectric composition containing barium titanate (BaTiO ₃ ) as a main component.
Since the outer surface layer made of a dielectric material containing 90% by weight of stabilized zirconia is integrated, it has a high dielectric constant of excellent mechanical strength without affecting the electrical characteristics of the dielectric material. Since a ceramic capacitor can be obtained, it is extremely useful as an in-vehicle electronic component that requires high reliability, and is particularly suitable for an in-vehicle laminated capacitor and the like.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a ceramic capacitor of the present invention.

[Explanation of symbols]

 1 Ceramic Capacitor 2 Dielectric Layer 3 Internal Electrode Layer 4 Multilayer Capacitor 5 Upper Surface 6 Lower Surface 7, 8 Outer Surface Layer

Claims (3)

[Claims] To claim 1, wherein at least upper and lower surfaces of the multilayer capacitor dielectric layers and internal electrode layers mainly composed of barium titanate (BaTiO ₃₎ are alternately stacked, composed mainly of barium titanate (BaTiO ₃₎ A ceramic capacitor comprising an outer surface layer containing 40 to 90% by weight of stabilized zirconia in a dielectric composition. 2. The content of the stabilized zirconia is 50 to 7
The ceramic capacitor according to claim 1, wherein the ceramic capacitor is 5% by weight. 3. The ceramic capacitor according to claim 1, wherein the stabilized zirconia is 8 mol% yttria-stabilized zirconia (hereinafter referred to as 8YSZ).