JPH0332009A - Capacitor and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a capacitor wherein the edge effect is not generated and which has high dielectric constant and excellent electric characteristics by providing a pair of electrodes on both surfaces of a ceramic substrate, and forming the end surface of the substrate with an insulator body part having low dielectric constant. CONSTITUTION:A capacitor 1 is formed of a pair of electrodes 3a and 3b which are provided on both surfaces of a ceramic substrate 2 and an insulator part 4 which surrounds the side surface of the substrate 2. The substrate 2 is formed of a region having high dielectric constant. The region is formed by baking a grain-boundary-layer type ceramic molded body and made to be a semiconductor. The electrodes 3a and 3b are formed of a conductive metal. The part 4 is formed of a sintered region having low dielectric constant. The region is formed by baking insulated paste and is not made to be a semiconductor. Thus, the grain boundary which is grown in the ceramic substrate is confined in the insulator part. An edge effect by which an electric field leaks from the end surface to the outside is not generated. The electric characteristics such as the dielectric constant are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a capacitor, and more particularly, to a capacitor in which a pair of upper and lower electrodes are formed on a grain boundary insulating layer type ceramic substrate, and a method for manufacturing the same.

Semiconductor ceramics with insulating layers formed at grain boundaries generally have a large dielectric constant. If such a semiconductor ceramic is used, a capacitor with a large capacity can be obtained.

FIG. 4 shows a sectional view of this type of capacitor, which has a grain boundary insulating layer type ceramic substrate 5.
A pair of upper and lower electrodes 52a and 52b are formed on both the front and back surfaces of the substrate.

As the ceramic raw material for forming the ceramic substrate 51, materials containing barium titanate (BaTiOi) as a main component have been widely used.

However, this BaTi0z-based capacitor has a large dielectric constant of about 70.000, but has a large dielectric loss of 5 to 6% (I KHz), and furthermore, the temperature change rate of capacitance is only 20°C. -25 to +85 when based on
It has the disadvantage that it is as large as ±50% in the temperature range of °C.

Therefore, in recent years, attempts have been made to improve electrical properties such as the dielectric loss and temperature change rate of capacitance mentioned above.
Capacitors based on strontium titanate (SrTiOsl) have been developed.

However, even this ceramic capacitor mainly composed of 5rTi (h) has the following drawbacks.
When a capacitor is constructed by adding Ta to the main component consisting of 0mo1%, the dielectric loss shows a good value of 0.5%, and the temperature change rate of capacitance is -25 to +85℃.
The dielectric constant is improved to within 10% in the temperature range of 30%.
,000, which is low.

■In addition, in ceramic capacitors made by adding Nb to the ceramic raw material whose main component is 5rTiOz, the dielectric constant is improved to 50.000 or more, and the dielectric loss is also a good value of 1% or less. The rate of temperature change is 125
It increases to ±13% or more in the temperature range of ~+85°C.

■Furthermore, in Japanese Patent Application Laid-Open No. 54-78498,
A capacitor has been disclosed in which an insulating layer made of Bi, Mn, etc. is formed at the grain boundaries of a SrTiO3 ceramic containing Mn, Ta, etc.;
Although the dielectric loss and the temperature change rate of capacitance are good, the dielectric constant is only about 53,000 at most.

■In addition, in Japanese Patent Application Laid-open No. 63-17256, T.
For the main components consisting of iO□ and SrO, MnO2,
A capacitor containing SiO□ and WOs has been disclosed, but like the above-mentioned capacitor, this capacitor exhibits good values for dielectric loss and rate of change of capacitance with temperature, but has a dielectric constant of 65. It has improved only to about 000.

In this way, in conventional capacitors, BaTi0a
Although the system capacitor has a high dielectric constant, there are problems in that it has a large dielectric loss and a large temperature change rate of capacitance. On the other hand, although the dielectric loss and the temperature change rate of capacitance are improved in the 5rTi03 series capacitor, there is a problem in that the dielectric constant decreases.

Furthermore, more recently, attempts have been made to improve the electrical characteristics by improving the composition of the components.
At present, the dielectric constant is limited to about 90,000.

In view of these problems, it is an object of the present invention to provide a capacitor that can improve the dielectric loss and the rate of change of capacitance with temperature, as well as obtain a larger dielectric constant, and a method for manufacturing the same.

To achieve the above object, the present invention provides a capacitor in which a pair of upper and lower electrodes are formed on a grain boundary insulating layer type ceramic substrate, in which the end face of the ceramic substrate has a low dielectric constant. It is characterized by being formed from a oxidized insulator part.

In addition, the method for manufacturing a capacitor according to the present invention includes Aj, O
a step of applying an insulating paste containing at least one component among s, SiO□, and MgO to the end face of the ceramic molded body, and firing the ceramic molded body coated with the insulating paste to obtain a sintered body. and a step of forming an electrode on the sintered body.

Note that the end surface of the ceramic substrate herein refers to the side wall surface on which the upper and lower pair of electrodes are not formed.

According to the above configuration, since the end face of the ceramic substrate is formed of an insulator portion with a low dielectric constant, the grain boundaries grown within the ceramic substrate are confined in the insulator portion, and the electric field is applied to the end face. There is almost no edge effect leaking to the outside, and electrical properties such as dielectric constant are improved.

Further, according to the above-described capacitor manufacturing method, AjJ
After applying an insulating paste containing at least one component among S, SiO□, and MgO to the end face of the ceramic molded body, an insulating part is formed by firing it,
Furthermore, by forming electrodes on the fired sintered body, a capacitor with excellent electrical properties can be easily manufactured.

Checkout Hereinafter, embodiments of the present invention will be explained in detail based on the drawings.

In FIGS. 1 and 2, l is a dielectric ceramic capacitor showing one embodiment of the capacitor according to the present invention. That is, the capacitor l includes a ceramic substrate 2, a pair of upper and lower electrodes 3a and 3b formed on both the front and back surfaces of the ceramic substrate 2, and an insulator portion formed on the end surface of the ceramic substrate 2 and surrounding the ceramic substrate 2. It is composed of 4.

The ceramic substrate 2 is formed by firing a ceramic molded body mainly composed of 5rTi(h, BaTiOs, etc.), and has a high dielectric constant region made into a semiconductor.

Further, the electrodes 3a and 3b are made of a conductive metal such as Ag or Cu.

Furthermore, the insulator portion 4 is made of ARzOs, SiO□, Mg
An insulating paste containing at least one component of O is fired to form a low dielectric constant region that is sintered without becoming a semiconductor.

Next, a method for manufacturing the above-mentioned capacitor will be explained in detail based on FIG.

(I) First, a ceramic molded body is manufactured.

That is, valence control agents (for example, La, Dy, Nd, Y, Nb,
Oxides of Ta, Er, Gd, No, Ce, etc.)
After mixing sintering aids (oxides such as Cu and Mn) that improve the properties of ceramics and stabilize their properties into the specified ceramic raw materials, they are formed into sheet shapes by press molding or extrusion molding. Manufacture the body.

Next, this sheet-like molded body is pressed into a predetermined shape using a mold press.

Here, as the ceramic raw material, for example, BaTiO
s, 5rTiOi, MgTi0a, (Ba, Srl
(Ti, Snl Oa-based composite oxide (including solid solution)
．． (Ba, 5rlTiO3 complex oxide (including solid solution), (14g, Sr, CaJTiOa complex oxide (including solid solution), (Sr, Pbl Tie,
system complex oxide (including solid solution, (Sr, Ca)
TLO3-based composite oxide (including solid solution), FeJ3,
One or more dielectric components such as ZnO1SiJ4 are used.

(If) Next, an insulating paste is applied to the end face of the ceramic molded body.

Here, as the insulating paste, AgxOs and Si are suitable for forming an insulator portion with a low dielectric constant.
A material containing at least one component of O□ and MgO is used.

(III) Next, this is subjected to second firing.

That is, the ceramic molded body coated with the insulating paste was placed in a reducing atmosphere (821 to 15 vol%, Na99
~85vo1%), firing is performed at a temperature of 1400 to 1540°C for 4 to 6 hours to obtain a sintered body. Through this second firing, the parts to which the insulating paste is not applied are made into semiconductors, the growth of crystal grains is promoted, and a ceramic substrate 2 having a high dielectric constant is formed.
The growth of crystal grains is suppressed in the portion where the insulating paste is applied, and an insulator portion 4 having a low dielectric constant is formed without being converted into a semiconductor.

(IV) Next, a metal oxide (e.g. Bi*Oi, CuO, NaxO1MnOi) is added to the surface of this sintered body as an additive.
, TlzOs, PbO1NbzOs, ZnO, etc.).

This additive is added in order to smoothly form an insulating layer at grain boundaries to obtain a ceramic capacitor having desired electrical characteristics.

(V) Next, this is subjected to secondary firing.

That is, heat treatment is performed in the air at a temperature range of 1000 to 1300°C. Through this secondary firing, the above-mentioned additive is diffused between the crystals in the ceramic substrate 2, and the grain boundaries are insulated. .

(Vl) Next, a conductive metal paste is applied to both the front and back surfaces of the ceramic substrate 2 by screen printing or the like, and then baked to form the electrodes 3a and 3b, completing the production of the ceramic capacitor.

Here, the metal paste includes Ag, Au, Z
A material containing at least one of n or Ni is used. However, in consideration of electrical properties etc., it is most desirable to use Ag, and the baking of the metal paste is carried out in the air at a temperature of 700 to 900°C.

Next, based on the steps (I) to (vl) above, 5rTiO
A specific example of manufacturing an s-based ceramic capacitor will be described.

Mix ceramic raw materials to a predetermined composition ratio.

That is, TiO□, 5rO1C are used as ceramic raw materials.
aO is used as the main component, and its composition ratio is Ties50.
．． 0~52.0mo1%, Sr040.0~50.0m
o1% and Ca00 to 10.0 mo1%.

Next, Nb is added to the ceramic raw material as a valence control agent.
After mixing about 0.1 to 0.5 mo1% of Js, YJs, etc. and about 0.05 to 0.4 mo1% of CuO1Mn0a etc. as a sintering aid, these were mixed together with a binder, water, and a dispersant. Thereafter, a sheet-like ceramic molded body was manufactured by press molding or extrusion molding.

Furthermore, after this, the sheet-like molded body was pressed into a ceramic molded body of a predetermined shape using a mold press.

Next, an insulating paste containing at least one component among A1.03, SiO□, and MgO was applied to the outer periphery of the end face of the ceramic molded body.

After that, the ceramic molded body coated with the insulating paste was placed in a reducing atmosphere (Hz: 1 to 15 vo1%).
, N, : 85-99vo1%) from 1400 to
Secondary firing was performed at a temperature of 1540° C. for 4 to 6 hours to obtain a sintered body.

After the primary firing, when the cross section of the sintered body was observed using a SEM, it was found that the part to which the insulating paste was applied had a crystal grain size of 2 to 4 μm, and the part to which the insulating paste was not applied was as follows. The crystal grain size was 50 to 200 μm. In other words, crystal grains do not grow in the portion where the insulating paste is applied, forming an insulator portion 4 with a low dielectric constant. On the other hand, crystal grains grow in the portions to which the insulating paste is not applied, forming a ceramic substrate 2 having a high dielectric constant. When the dielectric constants of the insulator portion 4 and the ceramic substrate 2 were measured, the dielectric constant of the insulator portion 4 was about 300 to 1500, and the dielectric constant of the ceramic substrate was about 50,000 to 150,000. Met.

Next, a mixed paste (additive) of B110i, CuO1Na*0, etc. is applied thereto, and then secondary firing is performed.

The conditions for this secondary firing are a temperature of 1000 to 1300°C and a firing time of about 1 hour. And, through this secondary firing,
The ions of the additive component diffuse between the crystals in the ceramic substrate 2, and the grain boundaries are insulated.

Next, after applying Ag paste as a metal paste to both the front and back surfaces of the ceramic substrate 2, baking was performed to form electrodes 3a and 3b, thereby manufacturing a ceramic capacitor 1. Incidentally, the baking was performed in the air at a temperature of 700 to 900°C.

Table 1 shows the electrical characteristics (permittivity, dielectric loss, and temperature characteristics of capacitance) when ceramic capacitors are formed by changing the composition ratio of the insulating paste in conventional examples where the insulator portion 4 is not formed. (Fig. 4).

Here, the dielectric constant ε and dielectric loss tan δ (%) are 1 kHz.
z was determined from the value measured under an alternating current voltage of 1v. Also,
The insulation resistivity ρ was determined from the current value after applying a DC voltage of 25 V for 1 minute. Furthermore, the temperature change rate (%) of capacitance is determined by measuring the capacitance when cooled to -25°C and when heated to +85°C, and comparing the capacitance at +25°C. , calculated from the difference.

For No. 1 to No. 6, the insulating paste is At20
s, 5ift, MgO, or a mixture thereof; No. 7 to No. 12 are At20s, etc., MnC0z
No. 13 to No. 16 are cases in which Bi was mixed into AffiJs etc.
The case where 20g is mixed is shown.

No. 17 is a conventional example in which the ceramic substrate 2 is not surrounded by the insulator portion 4 (see FIG. 4).

As is clear from Table 1, the capacitor of the present invention (
No. l ~ No. 16) has a dielectric loss of 0.7
% or less, the insulation resistivity is 1.3X to "Ωcm or more, and the temperature change rate of capacitance is within ±1O15%, which shows good electrical properties.
It can be seen that the improvement was 7 to 56% compared to No. 17).

It was also found that when an insulating paste containing a Mn compound was used, the insulation resistivity was significantly improved.

It goes without saying that the present invention is not limited to the above-mentioned embodiments, and can be modified without departing from the scope of the invention. The ceramic raw material is not limited to 5rTiOz type ceramic raw materials, and the intended purpose of the present invention can be achieved even if BaTiO3 type or other ceramic raw materials are used.

SUMMARY OF THE INVENTION As described in detail above, the present invention provides a capacitor in which a pair of upper and lower electrodes are formed on a grain boundary insulating layer type ceramic substrate, in which the end face of the ceramic substrate is made of an insulator with a low dielectric constant. Since the grain boundaries grown in the ceramic substrate are confined in the insulating part, the ceramic substrate has almost no edge effect, has a large dielectric constant, and has excellent electrical properties such as dielectric loss. You can get a capacitor.

In addition, the above capacitor is Aja03.5iOz, Mg
An insulator portion can be easily formed by applying an insulating paste containing at least one component of O to a ceramic molded body and firing it, and further forming an electrode on the fired sintered body. This makes it simple and easy to manufacture.

As described above, according to the present invention, it is possible to obtain a capacitor having good dielectric loss, good temperature change rate of capacitance, or insulation resistivity, and having a larger dielectric constant.

Moreover, without changing the composition of conventional capacitors,
An excellent capacitor can be simply and easily manufactured by simply adding the step of applying an insulating paste to the end face of a ceramic substrate.

[Brief explanation of drawings]

FIG. 1 is a sectional view (A-A sectional view in FIG. 2) showing an embodiment of a capacitor according to the present invention, FIG. 2 is a plan view showing an embodiment of a capacitor according to the present invention, and FIG. is a manufacturing process diagram for explaining the method for manufacturing a capacitor according to the present invention,
FIG. 4 is a sectional view showing a conventional capacitor. 2... Ceramic substrate, 3a, 3b... Electrode, 4...
...Insulator part. Figure 1 Figure 2-4-

Claims (2)

[Claims] (1) A capacitor in which a pair of upper and lower electrodes are formed on a grain boundary insulating layer type ceramic substrate, characterized in that the end face of the ceramic substrate is formed of an insulator portion with a low dielectric constant. . (2) Applying an insulating paste containing at least one component among Al_2O_3, SiO_2, and MgO to the end face of the ceramic molded body, and firing the ceramic molded body coated with the insulating paste to sinter it. A method for manufacturing a capacitor, comprising: obtaining a sintered body; and forming an electrode on the sintered body.