JPH03145108A - Capacitor and manufacture thereof - Google Patents

Abstract

PURPOSE:To reduce the irregularity of permittivity and to obtain a capacitor having more excellent dielectric characteristics by a method wherein a ceramic substrate is composed of a semiconductive high permittivity region and an insulating low permittivity region, and capacitance is finely adjusted by use of the low permittivity region. CONSTITUTION:A part of the surface of a ceramic molded body is coated with the material as insulating paste, containing the ingredient consisting of at least one or more selected from Al2O3, SiO2 and MgO, its primary firing operation is conducted, the part on which insulating paste is not coated is brought into a semiconductive state, a high permittivity region 4 is formed, and an insulating low permittivity region 5 is formed on the part where insulating paste is coated. Then, the surface of the above-mentioned sintered body is coated with metal oxide, a secondary firing operation is conducted thereon, and a grain boundary insulated layer is formed between crystals in the high permittivity region. Then, after both front and rear sides of a ceramic substrate 2 have been coated with conductive metal paste, a baking operation is conducted, electrodes 3a and 3b are formed, and capacitance is finely adjusted in a low permittivity region 5.

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 insulated ceramic substrate, and a method for manufacturing the same.

The semiconductor ceramic in which an insulating layer is formed on the grain boundaries of the crystal grains is -M.
It has a large dielectric constant. If such a semiconductor ceramic is used, a capacitor with a large capacity can be obtained.

FIG. 4 shows a cross-sectional view of this type of capacitor, which includes a grain-boundary insulated ceramic substrate 51.
A pair of upper and lower electrodes 52a and 52b are formed on both the front and back surfaces of the board.

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

However, although this BaTiOs-based capacitor has a fairly large dielectric constant of about 70,000, it has a large dielectric loss of 5 to 6% (lkHz), and the rate of change of capacitance with temperature is based on 20°C. In this case, -25 to +8
It has the disadvantage that it is as large as ±50% in the range of 5°C.

Therefore, in recent years, capacitors containing strontium titanate (SrTiOs) as a main component have been developed in an attempt to improve dielectric properties such as dielectric loss and temperature change rate of capacitance.

In the ceramic capacitor mainly composed of SrTiOs, the dielectric loss is as small as about 0.5%, and the temperature change rate of capacitance is in the range of -25 to +85°C when 20°C is the standard. within ±15%.

However, the SrT i Oa capacitor has a large crystal grain size of 50 μm to 100 μm, and the dielectric constant increases approximately in proportion to the average crystal grain size, so it is difficult to obtain a capacitor with a high dielectric constant of about 109,000. On the other hand, the variation in dielectric constant also increases approximately in proportion to the average crystal grain size. That is, in the 5rTiO type capacitor, Ba
Although the dielectric loss and the temperature change rate of capacitance are improved compared to TiO3-based capacitors, the variation in dielectric constant becomes larger, so there is a problem that the variation in capacitance as a capacitor increases.

In view of these problems, it is an object of the present invention to provide a capacitor that reduces variations in dielectric constant and has even better dielectric properties, and a method for manufacturing the same.

In order to achieve the above object, a capacitor according to the present invention is a capacitor in which a pair of upper and lower electrodes are formed on a grain boundary insulated ceramic substrate, in which the ceramic substrate is made into a semiconductor. It consists of a high dielectric constant region and a low dielectric constant region made into an insulator, and is characterized in that the capacitance is finely adjusted by the low dielectric constant region.

Further, in the method for manufacturing a capacitor according to the present invention, Aug.
a step of applying an insulating paste containing at least one component selected from Os, SiO2, and Mgo; a step of firing the ceramic molded body coated with the insulating paste to obtain a sintered body; The method is characterized in that it includes a step of forming an electrode on the sintered body.

Biri According to the above configuration, since the ceramic substrate is composed of a high dielectric constant region made into a semiconductor and a low dielectric constant region made into an insulator, most of the predetermined capacitance is in the high dielectric constant region made into a semiconductor. Obtained from the dielectric constant region. Since the capacitance is finely adjusted in the low dielectric constant region, a capacitor with less variation in capacitance can be obtained.

Further, according to the above-described capacitor manufacturing method, AQm
A high dielectric constant region and a low dielectric constant region are formed by applying an insulating paste containing at least one component selected from Os, SiOs, and MgO to a part of the surface of the ceramic molded body, and then firing it. A mixed ceramic substrate (sintered body) is obtained, and by further forming electrodes on the sintered body, a capacitor with excellent dielectric properties can be easily manufactured.

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

In FIGS. 1 and 2, reference numeral 1 denotes a dielectric ceramic capacitor showing an embodiment of the capacitor according to the present invention, and the capacitor 1 includes a ceramic substrate 2 and a ceramic substrate formed on both the front and back surfaces of the ceramic substrate 2. A pair of upper and lower electrodes 3
a, 31).

The electrodes 3a and 3b are made of conductive metal such as Ag and Cu.

The ceramic substrate 2 is composed of a high dielectric constant region 4 and a low dielectric constant region 5, and the high dielectric constant region 4 is made of 5rTi.
A ceramic molded body whose main component is a ceramic raw material such as Oa, BaTiO2, etc. is fired and turned into a semiconductor. Further, the low dielectric constant region 5 is formed by firing a ceramic molded body whose surface is coated with an insulating paste, and is sintered and made into an insulator without being made into a semiconductor.

The low dielectric constant region 5 is formed to finely adjust the capacitance, and in this embodiment, it is formed on the end face of the high dielectric constant region 4, but it is formed on a part of the ceramic substrate 2. It would be fine if it had been done.

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

CI) First, a ceramic molded body is manufactured.

Valence control agents (e.g. La, Dy, Nd, Y, Nb) that contribute to converting ceramic raw materials into semiconductors.

Oxides such as Ta, Er, Gd, Ho, Ce, etc.) and sintering aids (oxides such as Cu, Mn, etc.) that act to improve and stabilize the properties of ceramics are mixed into specified ceramic raw materials. After that, a sheet-like molded body is produced by press molding or extrusion molding.

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, 5rTiOa, (Ba, 5r)(Ti, 5n)O
x-based composite oxide (including solid solution), (Ba, 5r)Ti
es-based composite oxide (including solid solution), (Mg, Sr, C
a) Ties-based composite oxide (including solid solution), (S r
, Pb) TiOs-based composite oxide (including solid solution), (Sr, Ca)Ti○, one type of dielectric component such as LFei O3, ZnO, Sis N4, etc. Use two or more types.

(II) Next, an insulating paste is applied to a part of the surface of the ceramic molded body.

The insulating paste is used to form a low dielectric constant region in order to suppress variations in capacitance as much as possible, and is used to form a low dielectric constant region on a part of the surface of the ceramic molded body, such as the end face or middle part of the ceramic molded body. Apply to the area.

Insulating pastes suitable for forming the above-mentioned low dielectric constant region include A, LOa, 5iOs, and MgO.
Among them, those containing at least one kind of component are used.

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

The ceramic molded body having an insulating paste applied to a part of its surface was heated in a reducing atmosphere (H*: 1 to 15 vol%, N
a: 99-85 vo1%), 1400
Firing is performed at a temperature of -1540°C for 4 to 6 hours to obtain a sintered body. By this second firing, the parts to which the insulating paste is not applied are converted into semiconductors, the growth of crystal grains is promoted, and high dielectric constant regions 4 are formed, and the parts to which the insulating paste is applied are made into semiconductors. Growth of crystal grains is suppressed,
Low dielectric constant region 5 that is made into an insulator without being made into a semiconductor
is formed.

(+V) Next, a metal oxide (e.g. Bia03.CuO, NaaO, Mn0
a, T to lx Oa, Pbo, Nag Os, Zn
O, etc.).

This additive is added to smoothly form an insulating layer at grain boundaries to obtain a ceramic capacitor having desired dielectric properties.

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

Heat treatment is performed in the air at a temperature range of 1000 to 1300°C. By this secondary firing, the additive is diffused between the crystals in the high dielectric constant region 4, the grain boundaries are insulated, and a grain boundary insulating layer is formed.

(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 used includes at least 61 types of Ag, Au, Zn, or Ni. However, in consideration of electrical characteristics etc., it is most desirable to use Ag. Further, the metal paste is baked in the atmosphere at a temperature of 700 to 900°C.

In the capacitor formed in this manner, most of the predetermined capacitance is obtained in the high dielectric constant region 4, and the capacitance obtained from the low dielectric constant region 5 is small.

That is, since the capacitance obtained from the low dielectric constant region 5 and the electrodes 3a and 3b located on both the front and back surfaces of the low dielectric constant region 5 is small, the capacitance is finely adjusted in the low dielectric constant region 5. Therefore, a capacitor with less variation in capacitance can be obtained. That is, by manufacturing the ceramic substrate 2 in which the high dielectric constant region 4 and the low dielectric constant region 5 are mixed, a capacitor having a large capacitance and a small variation in capacitance can be obtained.

Next, based on the steps (I) to (Vl) above, 5rTi○
A specific example of manufacturing a ceramic capacitor based on the following will be described.

Mix ceramic raw materials to a predetermined composition ratio.

That is, T i O*, SrO as ceramic raw materials
, CaO is used as the main component, and its composition ratio is Ti0z
50.0-52.0 mo1%, 5rO40.0-5
The content was adjusted to 0.0 mo1% and Ca0O to 10.0 mo1%.

Next, N is added to the ceramic raw material as a valence control agent.
biOs, Y20s, etc., O, 1-0.5mol1%,
CuO5MnO* etc. as a sintering aid from 0.05 to 0
．． 4. After mixing approximately 1% of rno, these were mixed together with a binder, water, and a dispersant. Thereafter, a sheet-like ceramic molded body was produced by press molding or extrusion molding.

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

Next, an insulating paste containing at least one component selected from Af220s, 5iOa, and MgO was applied to a part of the surface of the ceramic molded body.

After that, the ceramic molded body coated with the insulating paste was heated in a reducing atmosphere with CH2:1 to 15vo1%.
l'L2: 140 at 99n85vo1%)
Secondary firing was performed at a temperature of 0 to 1540°C for 4 to 6 hours to obtain a sintered body.

When the cross section of this sintered body was observed with an SEM after the second firing, it was found that the portion where the insulating paste was applied had a crystal grain size of 2 μm to 4 μm, and the portion where the insulating paste was not applied was found to be has a crystal grain size of 50 μm to 200 μm
It was m. That is, in the area where the insulating paste is applied, crystal grains do not grow, and the area becomes an insulator and forms the low dielectric constant region 5. On the other hand, crystal grains grow in the portions to which the insulating paste is not applied and are converted into semiconductors, forming high dielectric constant regions 4. Note that the dielectric constant of the low dielectric constant region 5 was about 300-1,500, and the dielectric constant of the high dielectric constant region 4 was about 50,000 to 150,000.

Next, after applying a mixed paste (additives) such as B is Ox, Cub, Nag O, etc., secondary firing is performed.The conditions for this secondary firing are a temperature of 1000 to 1300.
℃, and the firing time is about 1 hour. By this secondary firing, ions of the additive component diffuse between the crystals in the high dielectric constant region 4, insulating the grain boundaries and forming a grain boundary insulating layer.

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

Table 1 shows the dielectric properties (permittivity, dielectric loss, temperature change rate of capacitance, variation in capacitance) when ceramic capacitors are formed by varying the composition ratio of the insulating paste.
A conventional example in which the low dielectric constant region 5 is not formed (Fig. 4)
This is what I showed along with it. Here, the dielectric constant ε2 and the dielectric loss tan δ (%) were determined from values measured under an alternating current voltage of 1 kHz and 1 V. In addition, the insulation resistivity ρ is the DC voltage 25
It was determined from the current value after applying 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.
It was calculated from the difference between the capacitance and the capacitance at ℃.

(Hereinafter, blank space) No. 1-No. 6, the insulating paste is Affa O
s, SiOx, and MgO are shown. No. 7 to No.
12 shows the case where M n COs is mixed into the above-mentioned AI2*Os, etc., and No. 13 to No. 16 show the case where M n COs is mixed into the above-mentioned Aal! This shows a case where Bit○ is mixed in the OS etc.

No. 17 is a conventional example in which the low dielectric constant region 5 is not formed on the ceramic substrate 2 (see FIG. 4).

As is clear from Table 1, the capacitors (No. 1 to No. 16) according to the present invention have a dielectric loss of 0.
．． 7% or less, insulation resistivity is 1.3 x 10"Ω・cm or more, and the temperature change rate of capacitance is within ±10.5%, showing good dielectric properties, and the variation in capacitance is also lower than conventional It can be seen that this is suppressed compared to the example capacitor (No. 17).

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

It should be noted that the present invention is not limited to the above-mentioned embodiments, and can be modified without departing from the spirit of the invention. Further, the ceramic raw material is not limited to the 5rTiO8 type, and the intended purpose of the present invention can be achieved even if BaTiO3 type or other ceramic raw materials are used.

As detailed above, in the capacitor according to the present invention, in the capacitor in which a pair of upper and lower electrodes are formed on a grain-boundary isolated ceramic substrate, the ceramic substrate is Since it is composed of a dielectric constant region and a low dielectric constant region made into an insulator, most of the predetermined capacitance is obtained from the high dielectric constant region. Further, since the capacitance is finely adjusted in the low dielectric constant region, it is possible to obtain a capacitor with less variation in capacitance. Therefore, a capacitor having a large dielectric constant, excellent dielectric properties such as dielectric loss, and less variation in capacitance can be obtained.

Further, the above-mentioned ceramic substrate in which a low dielectric constant region and a high dielectric constant region are mixed is obtained by applying an insulating paste containing at least one component among AgaOs, 5toz, and Mgo to a part of the surface of the ceramic molded body. After that, the capacitor can be easily produced by forming electrodes on the ceramic substrate (sintered body).

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

[Brief explanation of the drawing]

FIG. 1 shows a second embodiment of a capacitor according to the present invention.
2 is a plan view showing an embodiment of the capacitor according to the present invention, FIG. 3 is a manufacturing process diagram for explaining the manufacturing method of the capacitor according to the present invention, and FIG. FIG. 2 is a cross-sectional view showing a conventional capacitor. 2... Ceramic substrate, 3a, 3b... Electrode, 4...
...High dielectric constant region, 5...Low dielectric constant region.

Claims (2)

[Claims] (1) In a capacitor in which a pair of upper and lower electrodes are formed on a grain-boundary insulated ceramic substrate, the ceramic substrate is composed of a high dielectric constant region made into a semiconductor and a low dielectric constant region made into an insulator. , a capacitor characterized in that capacitance is finely adjusted by the low dielectric constant region. (2) a step of applying an insulating paste containing at least one of Al_2O_3, SiO_2, and MgO to a part of the surface of the ceramic molded body containing the semiconducting agent; a step of firing the ceramic molded body to obtain a sintered body; and a step of forming an electrode on the sintered body. A method for manufacturing a capacitor, comprising: