JPH0785459B2 - Grain boundary insulation type semiconductor ceramic capacitor - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a grain boundary insulation type semiconductor ceramic capacitor such as a strontium titanate ceramic capacitor.

[0002]

2. Description of the Related Art SrTiO ₃ or Sr _1-x Ba _x TiO 2
₃ , or Sr _1-y Ca _y TiO ₃ , or Sr _1-xy Ba
The _x Ca _y TiO ₃ as a main component, Y ₂ O _3, La
Grains using at least one of ₂ O ₃ , Nb ₂ O _{5 and the} like as a semiconducting component and at least one of Bi ₂ O ₃ , PbO, CuO, B ₂ O _{3 and the} like as a grain boundary insulating material Field-insulating semiconductor ceramic capacitors are known. This type of grain boundary insulation type semiconductor ceramic capacitor has a ceramic base and at least two electrodes, and the ceramic base is composed of a large number of semiconductor particles and an insulating layer between the semiconductor particles.

The grain boundary insulating layer has a thickness of 0.1 to 0.2.
It has a thickness of μm.

[0004]

By the way, in the grain boundary insulation type semiconductor ceramic capacitor, a microcapacitor consisting of a semiconductor grain acting as an electrode of the microcapacitor and a grain boundary insulating layer acting as a dielectric is provided between a pair of electrodes. A plurality of them are arranged in series. Therefore, when the number of minute capacitors between the pair of electrodes is increased, the capacity of the capacitors is reduced as a result. Therefore, when trying to obtain a high relative dielectric constant, the diameter of the semiconductor particles is made relatively large, or the thickness of the porcelain body is made small, so that the semiconductor particles and the grain boundary insulating layer existing between the pair of electrodes are The number, that is, the number of minute capacitors can be suppressed. When the number of grain boundary insulating layers interposed between the pair of electrodes is reduced, the dielectric breakdown voltage is lowered.

Therefore, an object of the present invention is to provide a grain boundary insulation type capacitor which has a large product of the relative dielectric constant and the dielectric breakdown voltage used for evaluation of the capacitor.

[0006]

The present invention for achieving the above object provides a semiconductor ceramic substrate comprising a large number of semiconductor particles and a grain boundary insulating layer between the large number of semiconductor particles.
A grain boundary insulation type semiconductor ceramic capacitor comprising at least two electrodes provided on the semiconductor ceramic base,
The present invention relates to a grain boundary insulating type semiconductor ceramic capacitor in which the thickness of the grain boundary insulating layer is 500 angstroms or less.

[0007]

According to the present invention, by suppressing the thickness of the grain boundary insulating layer to 500 angstroms (0.05 μm) or less, the capacity of one grain boundary insulating layer can be increased. Thereby, a high relative dielectric constant can be obtained without reducing the number of grain boundary insulating layers between the pair of electrodes, and even if more semiconductor particles and grain boundary insulating layers are arranged between the pair of electrodes. Since the decrease in capacitance due to the increase in the number of grain boundary insulating layers can be canceled by the increase in the relative dielectric constant, the dielectric breakdown voltage between the pair of electrodes can be increased and the reliability can be improved. Therefore, a porcelain capacitor having a large value of the product εE of the dielectric constant ε and the dielectric breakdown voltage E can be obtained.

The thickness of the grain boundary insulating layer is 100 to 500.
It is desirable that the range is about angstrom. If the thickness of the grain boundary insulating layer is greater than 500 angstroms, the relative permittivity of the porcelain substrate becomes too small. Therefore, in order to obtain the desired capacitance, the number of semiconductor particles between the pair of electrodes must be reduced. It must be reduced, and the dielectric breakdown voltage E is reduced accordingly, and the value of εE is also reduced.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The grain boundary insulating type semiconductor ceramic capacitor 1 according to Examples and Comparative Examples is shown in principle in the drawings. This porcelain capacitor 1 comprises a disc-shaped porcelain base 2 and a pair of electrodes 3,
It consists of 4 and. The porcelain substrate 2 has a large number of semiconductor particles 5 and
And the grain boundary insulating layer 6 between them. The semiconductor particles 5 function as a conductor, and the grain boundary insulating layer 6 functions as a dielectric. Therefore, a plurality of minute capacitors are arranged between the pair of electrodes 3 and 4. The dimensions of the porcelain substrate 2 before firing are 10 mm in diameter and 0.45 mm in thickness.

Fifteen types of porcelain capacitors having the same outer shape and size, although the composition of the porcelain substrate 2, the diameter of the semiconductor particles 5 and the thickness of the grain boundary insulating layer 6 were different, were prepared. Table 1 is 1
The composition of five types of porcelain capacitors is shown below.

The porcelain substrate 2 of the porcelain capacitor in this embodiment is composed of a main component, a semiconductor component and a grain boundary insulating material. The main component and the semiconducting component can be combined and shown by the following formula. _{Sr 1-xy Ba x Ca y} TiaO 3 + bM above equation the first term of _{Sr 1-xy Ba x Ca y} TiaO 3 shows the main component. Sr in this main component is strontium, B
a is barium, Ca is calcium, Ti is titanium, O is oxygen, and _1-xy , x, and y are numerical values showing the proportions of Sr, Ba, and Ca. a is Sr _1-xy Ba _x Ca _Y of Ti
Is a numerical value showing the ratio to.

M of bM representing a semiconducting component is at least one of Y ₂ O ₃ , La ₂ O ₃ , Nb ₂ O _{3 and the} like which are oxides of the semiconducting component. b is a numerical value showing the ratio of the semiconducting component M to the main component in mol.

Grain boundary insulating materials include Bi ₂ O ₃ (bismuth oxide), PbO (lead oxide), CuO (copper oxide) and B ₂ O.
_It consists of one selected from ₃ (boron oxide). In this embodiment, as will be apparent from the later description, the grain boundary insulating material is applied to the semiconductor ceramic substrate and heat-treated to diffuse into the ceramic substrate.

Table 1 shows the values of x, y, a of the equations showing the main components, the values showing the ratio b of the semiconducting component M, and the contents of M. In addition, grain boundary insulating materials Bi ₂ O ₃ and PbO
And the composition of CuO and B ₂ O ₃ are given in mol%.

[0015]

[Table 1]

Next, the porcelain capacitor of Sample No. 1 and its manufacturing method will be described. The main components of the porcelain capacitor of Sample No. 1 were x = 0 and y = 0 and did not contain Ba or Ca. Therefore, this main component is SrT _i O ₃ (strontium titanate). In order to obtain this SrTiO ₃ , each powder of SrCO ₃ (strontium carbonate) TiO ₂ (titanium oxide) is prepared as a starting material, and b in the composition formula is 0.001.
Y ₂ O ₃ (yttrium oxide) powder was prepared in such a ratio that That is, SrTiO ₃ + 0.001Y ₂ O
₃ To be able to obtain, SrCO _3, TiO _2,
Y ₂ O ₃ was prepared.

Next, SrCO ₃ , TiO ₂ and Y ₂ O ₃ were mixed and calcined at 1150 ° C. for 3 hours. next,
5% by weight of a polyvinyl alcohol solution as an organic binder was added to this calcined product for granulation.

Next, the granulated material is added at 1.5 ton / cm.
^A disc having a diameter of 10 mm and a wall thickness of 0.45 mm was formed at a forming pressure of ² . Next, in the air, 1100 ° C.
Heat treatment for 1 hour, and then N ₂ (99%) + H
145 in a reducing atmosphere consisting of a mixed gas of ₂ (1%)
A semiconductor porcelain substrate was obtained by firing at 0 ° C. for 2 hours.

Next, in order to insulate the grain boundary layer of the semiconductor ceramic substrate (sintered body), a grain boundary insulating substance having a composition of Bi ₂ O ₃ 80 mol% B ₂ O ₃ 20 mol% is prepared. A nitrocellulose-based organic binder and butyl carbitol were added to the grain boundary insulating material to form a paste.

Next, the paste of the grain boundary insulating material is applied to the porcelain substrate at a ratio of 5% by weight, and this is heat-treated in air at 1150 ° C. for 2 hours to form grain boundaries in the grain boundary layer 6. Insulating substances (Bi ₂ O ₃ , B ₂ O ₃ ) were diffused (permeated) to enhance the insulating property of the grain boundary insulating layer 6 shown in the figure.

Next, silver paste was applied to both main surfaces of the porcelain base body 2 and baked at 800 ° C. for 30 minutes to form a pair of electrodes 3 and 4 shown in the figure to complete the porcelain capacitor 1.

Also in Sample Nos. 2 to 15, a porcelain capacitor was prepared in the same manner as in Sample No. 1 except that the content or proportion of the main component, semiconducting component, or grain boundary insulating material was changed.

In the case of sample No. 3, x is 0.0
Therefore, the main component is represented by Sr _0.95 Ba _0.05 TiO ₃ . In order to obtain this main component, SrCO ₃ , BaCO ₃ (barium carbonate), TiO ₂ are used as starting materials.
To prepare.

Since y is 0.05 in Sample No. 14, the main component is represented by Sr _0.95 Ca _0.05 TiO ₃ . In order to obtain this main component, SrCO ₃ , CaCO ₃ (calcium carbonate) and TiO are used as starting materials.
Prepare ₂ . ,

In sample No. 15, since a is 0.995, the main component is SrTi _0.995 O ₃ .

Next, the apparent relative permittivity ε and the dielectric breakdown voltage E of the ceramic capacitors of each sample No. were measured. The apparent relative permittivity ε was measured under the conditions of + 20 ° C., frequency 1 kHz and voltage 0.5V. The dielectric breakdown voltage E was determined by applying a DC voltage to the pair of electrodes 3 and 4, gradually increasing the DC voltage, and measuring the voltage at the point where the current suddenly increased (breakdown point).

Further, a thin piece was made from the same porcelain substrate as the completed porcelain capacitor, and the size of the semiconductor particles 5 and the thickness of the grain boundary insulating layer 6 were measured by a transmission electron microscope (TEM). Since the semiconductor particles 5 are not perfect spheres but irregular polygons, the diameter of the circle in which the semiconductor particles 5 are inscribed determines the particle size of the semiconductor particles 5. Moreover, since the diameters of many semiconductor particles 5 in one porcelain substrate 2 are not the same, the average particle diameter was obtained. The thickness of the grain boundary insulating layer 6 is an average thickness between a large number of semiconductor particles 5.

Table 2 shows semiconductor particles 5 of sample Nos. 1 to 15.
Of the average grain size, the thickness of the grain boundary insulating layer 6, the relative permittivity ε,
The dielectric breakdown voltage E and the product ε × E of the relative dielectric constant ε and the dielectric breakdown voltage E are shown.

[0029]

[Table 2]

As is clear from Table 2, in the ceramic capacitor of Sample No. 1, the average particle size of the semiconductor particles 5 is 40 μm, the thickness of the grain boundary insulating layer 6 is 500 Å (0.05 μm), and the ratio is The dielectric constant ε is 70,000, the dielectric breakdown voltage E is 190 V, and the value of εE is 1.3 × 10 ⁷ .

In the present invention, the target is a ceramic capacitor having an εE value of 1.3 × 10 ⁷ or more. Therefore, sample No.
Those indicated by 2, 6, 8, 9, 10 do not meet the goals of the present invention.

As is clear from the relationship between the εE value and the thickness of the grain boundary insulating layer in Table 2, the thickness of the grain boundary insulating layer is 50.
The εE value of all the samples of 0 Å or less is 1.
It is 3 × 10 ⁷ or more. On the other hand, when the thickness of the grain boundary insulating layer exceeds 500 Å, the εE value is smaller than 1.3 × 10 ⁷ . Also, the εE value is 1.3 ×
The average particle size is 10 to 100 μm in samples of 10 ⁷ or more.
It is within the range of m.

[0033]

MODIFICATION The present invention is not limited to the above-mentioned embodiments, and the following modifications are possible.

The composition may be such that part of Sr in the main component is replaced with both Ba and Ca. That is, the main component is S
The composition may include all of r, Ba, Ca, and Ti.

The semiconducting component M is Y ₂ O ₃ , La ₂ O ₃ ,
It can be a plurality of combinations of Nb ₂ O ₃ . Furthermore, Nd ₂ O ₃ , Dy ₂ O ₃ and S are used as semiconductor components.
₃ such as m ₂ O ₄ , Pr ₂ O ₃ , Gd ₂ O ₃ and Ho ₂ O 3
Valent metal oxides, pentavalent metal oxides such as Ta ₂ O ₅ and combinations thereof can be used.

Bi ₂ O ₃ , Pb as grain boundary insulating material
In addition to O, CuO and B ₂ O ₃ , MnO ₂ , Tl ₂ O ₃ ,
Metal oxides such as Sb ₂ O ₃ , Fe ₂ O ₃ and combinations thereof can be used.

Instead of supplying the grain boundary insulating substance by coating with a paste, the grain boundary insulating substance is added to the calcined product of the main component and the semiconducting component, and this is molded and reduced or medium-sized. Alternatively, the grain boundary insulating layer 6 may be insulated by firing in an oxidizing atmosphere and then performing heat treatment in an oxidizing atmosphere. Insulation can also be achieved by combining the method of mixing the grain boundary insulating material with the raw material composition and the method of coating it with a paste.

[0038]

As is apparent from the above, according to the present invention, it is possible to provide a porcelain capacitor having a large product of the relative dielectric constant and the dielectric breakdown voltage.

[Brief description of drawings]

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

[Explanation of symbols]

 2 Porcelain substrate 3,4 Electrode 5 Semiconductor particle 6 Grain boundary insulating layer

Claims (1)

[Claims] 1. A grain boundary insulation comprising a semiconductor porcelain base comprising a large number of semiconductor particles and a grain boundary insulating layer between the plurality of semiconductor grains, and at least two electrodes provided on the semiconductor porcelain base. Type semiconductor ceramic capacitor, wherein the thickness of the grain boundary insulating layer is 500 angstroms or less.