JPH01175717A - Porcelain composition for reduction re-oxidation type semiconductor capacitor - Google Patents

Abstract

PURPOSE:To enable characteristics to be stable, insulation resistance to be improved, breakdown voltage to be improved, and mechanical strength of insula tion layer to be improved by adding a specified amount of manganese oxide to a material expressed by the general formula (Ba1-xSrx)m(Ti1-y-zZryMz)O3 and making the value within the expression to be within a specified range. CONSTITUTION:A manganese oxide of 0.05-0.2weight% (expressed in terms of to MnO2) is added to a material which is expressed by the general formula (Ba1-xSrx)m(Ti1-y-zZryMz)O3 (M is at least one of Ta and Nb and (m) is the total mol ratio of A site element and B site element) and the value of (m) within the expression is 0.990<=m<=1.000. For example, materials are subject to moisture mixture grinding so that the composition ratio (m) of [(Ba1-xSrx)m (Ti1-y-zZryMz)O3] may be equal to 0.995. The starting material is BaCO3, SrCO2, TiO2, ZrO2 and Ta2O5 with improved purity (99.8% or more) and x, y, and Z are equal to 0.200, 0.090 and 0.005, respectively. Also, a MnO2 of 0.1weight% is added to improve sinterability and insulation resistance. After that, a sintered porcelain is obtained through tentative burning, grinding, molding and calcina tion.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a reduction and reoxidation type semiconductor ceramic capacitor in which an insulating layer is formed on the outer periphery of barium titanate (B a TiO3) based semiconductor ceramic by reoxidation. Relating to a porcelain composition.

(Prior art and problems to be solved) There are various types of semiconductor ceramic capacitors.
A reduction and reoxidation type semiconductor ceramic capacitor has an insulating layer formed on the outer peripheral surface of a semiconductor ceramic, and an electrode for taking out the capacitance is formed on the outside of the insulating layer.

The manufacturing method includes, for example, adding rare earth elements such as La and Cs as a Curie point shifter to barium titanate porcelain, mixing, calcination, further shaping and firing to obtain sintered porcelain. .

It is heat-treated in a neutral or reducing atmosphere to convert it into a semiconductor, and then re-oxidized in an oxidizing atmosphere (for example, in air) to diffuse oxygen from the surface into the grains and form an insulating layer on the porcelain surface. By controlling the reoxidation conditions,
Varying the thickness of the IIA rim layer.

Capacity can be changed. After this, an electrode for taking out the capacitance is applied, but this method involves applying the electrode after re-oxidation treatment (for example, JP-A-59-217320, JP-A-60
-17908, No. 61-10225), and a method in which a silver electrode is coated and then reoxidized to diffuse the glass frit components to form a new insulating layer (for example, JP-A No. 6
1-191009).

In the case of the former method, if needle-shaped crystals or giant grains occur in the sintered porcelain, it will greatly affect the dielectric loss, 1M edge low resistance breakdown voltage, etc. A barium titanate system with a molar ratio of 8 A-site elements and B-site element of 1 is undesirable for reduction and reoxidation type semiconductor ceramic capacitors that are intended to obtain large capacity by using barium titanate.
When the size is larger, it becomes difficult to sinter, and when it is smaller than 1, giant grains and needle-shaped crystals tend to precipitate. Especially when adding elements such as shifters and depressors to barium titanate, the second phase appears easily, and is generally used in a state in which the second phase has precipitated. If there is non-uniformity such as the second phase, dielectric breakdown will occur from there, resulting in #! This will lead to deterioration of edge resistance, breakdown voltage, etc.
The method of applying electrodes after reoxidation treatment is not often used.

For this reason, a new insulating layer is generally formed by the latter method, but this method has problems in that the characteristics vary widely and the mechanical strength of the insulating layer is also extremely weak.

The present invention provides a novel reduction-reoxidation type semiconductor ceramic capacitor that eliminates the drawbacks of the above-mentioned conventional technology and enables improved stability of characteristics, improved insulation resistance, improved breakdown voltage, and improved mechanical strength of the insulating layer. The purpose is to provide

(Means for Solving the Problems) In order to achieve the above object, the present inventor has conducted extensive research on the porcelain composition and manufacturing process of conventional reduction-reoxidation type semiconductor ceramic capacitors.
A measure that can completely eliminate giant grains and needle-shaped crystals in the second phase that cause dielectric breakdown when the dielectric layer is thinned by reduction and reoxidation, and can obtain granular crystals with uniform and fine grain size. The present invention has been made based on this discovery.

That is, 1. The ceramic composition for a reduction and reoxidation type semiconductor ceramic capacitor according to the present invention has the general formula (B al-X
S rx) m (Ti, -y-z ZryMz) O
.

(However, M: at least one of Ta and Nb.

m: total molar ratio of the 8 A-site elements and the B-site element This is a material for a re-oxidized semiconductor ceramic capacitor, characterized in that 0.990≦m≦1.000.

The present invention will be explained in more detail below.

In the present invention, the 8 A-site elements include Ba and further contain Sr as a shifter, and the B-site element is Ti.
The main component is a barium titanate-based porcelain material represented by the above general formula, in which Zr and Zr are essential, and further contains at least one of Ta and Nb, and an appropriate amount of manganese oxide is added to this main component. It targets things.

Note that the molar ratio of Sr to Ba (X%), the molar ratio y of Zr to T1, and the molar ratio 2 of Ta and/or Nb can be determined as appropriate.

There are no particular restrictions. For example, 0.05≦X≦0゜50
．． 0.01≦y≦0.30.0.001≦2≦0.01
A range of 0 is desirable.

In addition, manganese oxide has sinterability, 1! It is added to improve edge resistance, and has a value of 0.0% in terms of manganese dioxide.
It is preferably added in an amount of 0.05 to 0.2% by weight. Note that if it is less than 0.05% by weight, high insulation resistance cannot be obtained;
．． If it exceeds 2% by weight, IR and tan δ will deteriorate. As manganese dioxide, Mn, O, or MnC0 can be added and calcined, and then mixed in a predetermined ratio based on M n O□.

In particular, the total molar ratio m of the 8 A-site elements and the B-site element
If it exceeds 1.000, it becomes difficult to sinter, and if it is less than 0.990, giant grains and needle-like crystals tend to appear, which is undesirable. By using a ceramic composition, it is possible to completely eliminate gigantic grains and acicular crystals of the second phase that cause dielectric breakdown when the dielectric layer is converted into a WI film by reduction and reoxidation. In particular, even when a shifter and a depressor are added to barium titanate as a base material, a relative dielectric constant of 12,000 or more near room temperature can be obtained, and the element body (sintered) has no second phase giant grains or needle-like crystals. By reducing and reoxidizing the solid porcelain (solid porcelain), it is possible to prevent the dielectric breakdown that conventionally occurs when a thin dielectric layer is made by reoxidation. In addition, it is no longer necessary to use the so-called diffusion of frit components, which performs electrode baking and reoxidation at the same time, so there is no need to use the so-called diffusion of the frit component, which is characteristic of reduction and reoxidation type semiconductor ceramic capacitors, and the mechanical weakness of the first surface dielectric layer is no longer a problem. It will stop happening.

In other words, it is possible to obtain a reduction and reoxidation type semiconductor ceramic capacitor that can be handled in the same way as a single capacitor.

Furthermore, by controlling the porcelain composition and manufacturing conditions, it is necessary to eliminate the giant grains and acicular crystals of the second phase, and to obtain uniform granular crystals with a grain size of 3μ or less. There is. If the sintered porcelain contains large grains with a grain size of more than 3 μI, the thickness of the insulating thin film layer after reoxidation will vary greatly, making it impossible to obtain a uniform insulating layer. 0.2-3
The μ-en range is preferred.

In order to obtain such granular crystals, sintered ceramics may be produced, for example, by the method shown below.

First, the raw material purity of each component of the A site and B site is 99.
8% or more, and the powder particle size is 0.0% because it is necessary to control the particle size of the sintered porcelain to 3 μm or less.
．． Use one with a thickness of 2 to 0.4 μm. Especially TiO2,Z
As for rO, a highly pure one with uniform particle size within this particle size range is used.

Next, by grinding the powder of each component in alcohol for a long period of time, such as 70 hours or more, uniform powder can be obtained, and the crystal grains of the sintered porcelain can have a grain size of 3 microns or less.

After mixing, calcination, pulverization, drying, granulation, molding, and firing are performed.
Drying after calcination and pulverization is done by rapid drying, instant drying, etc.
Powder free of agglomerated particles can be obtained, and the density of the sintered body can also be improved.

The obtained sintered porcelain was heated to neutral or H2, c.

The semiconductor material is reduced to a semiconductor in a reducing atmosphere such as the like, and then re-oxidized in the air to obtain a surface dielectric layer.

The attachment of the capacitance extraction electrode can be carried out by an appropriate method using the reoxidized dielectric layer as it is without requiring a method of diffusing the glass frit component in the electrode. It is also possible to bake in ohmic electrodes.

Next, examples of the present invention will be shown.

(Example) As a ceramic material for reduction-oxidation semiconductor ceramic capacitors.

(Ba1-x Srx)m (Ti, -y-zZryT
az)O.

The composition ratio m of the general formula is m=1.005.1.000.
The raw materials were wet-mixed and pulverized to give a powder of 0.995.0.990.0.985. The starting materials are high purity (99.8% or more) BacO, S r CO3, T i Oz, Z
Using rO2, Ta, ○, x=0.200. y=o.

090, z=o, o05. Furthermore, 0.1% by weight of MnOz was added to improve sinterability and insulation resistance.

Next, after mixing and drying, the mixture was calcined in air at 1200° C. for 2 hours, wet-pulverized, and instant-dried to obtain a product free of agglomerated particles. Next, a binder was added, granulation was performed, and veneer molding was performed. After that, all the molded bodies were heated to 1400'CX3h.
The mixture was fired at R to obtain sintered porcelain. The diameter of the porcelain is 6.4
(2) Thickness is about 0.91111.

Next, after a reduction treatment was performed in a reducing atmosphere and a reoxidation treatment in air, an ohmic silver electrode was baked as a capacitance extraction electrode.

Density ρ (g/cm') of sintered porcelain before reduction treatment.

Relative permittivity gr and dielectric loss tan δ (%) at 25°C
are also listed in Table 1. Also, the capacitance C (μF/cm”) of the obtained semiconductor ceramic capacitor.

Dielectric loss tan δ (%), insulation resistance CR (μF-MΩ
) and dielectric breakdown voltage Va (V) are shown in Table 2.
The relative dielectric constant sr, capacitance C, and dielectric loss tan δ are measured at a frequency of IKHz and a voltage of 1 V, and the insulation resistance CR is 50
After applying V and DC for 60 seconds, the dielectric breakdown voltage was D.
It was carried out using a C pressurization method. In addition, the capacitance was 0.25 (μF/
cm”).

From Table 1, it can be seen that when 1 m exceeds 1.010, the density decreases and a problem arises in sinterability. Also, if 1m is less than 0.990, that is, the B site side is excessive,
Although the dielectric constant improved, it was confirmed by optical microscopic observation that giant grains and needle-shaped crystals appeared prominently on the porcelain surface (Figure 2). Granular crystals are uniformly distributed, with an average grain size of 3
The tumor was smaller than a μ tumor (Fig. 1).

Furthermore, as is clear from Table 2, when the porcelain composition ratio m is out of the range of the present invention, the insulation resistance CR is particularly low.

The dielectric breakdown voltage Va has deteriorated. This is thought to be because the electrodes are ohmic, so giant grains and needle-like crystals appearing in one surface dielectric layer are responsible for the deterioration of the characteristics.

Furthermore, the dielectric loss tan δ has also deteriorated.

On the other hand, when the porcelain composition ratio m is within the range of the present invention, granular crystals are uniform and small in size, and the capacitance C is 0.25.
It can be seen that the dielectric breakdown voltage is 1100 V or more at (μF/c), which is a dramatic improvement in terms of characteristics.

[Blank 1 (Effects of the Invention) As detailed above, according to the present invention, the porcelain composition ratio m of the barium titanate-based semiconductor magnetic base material is strictly controlled, and the porcelain composition ratio m of the barium titanate-based semiconductor magnetic base material is strictly controlled. Since it is made of granular crystals with a fine grain size, the reoxidation insulating layer can be used in the same way as a single-plate capacitor, and the electrical properties 1 are reduced and reoxidized semiconductor ceramics with excellent characteristics that have significantly improved mechanical strength. You can get a capacitor. Performance is particularly demonstrated when an ohmic electrode is used as the electrode, and stability in terms of properties increases even during mass production, making it possible to suppress variations in properties as much as possible.

[Brief explanation of the drawing]

1 and 2 are micrographs showing the crystal structure of the surface of the sintered ceramic. FIG. 1 shows the case of the present invention, and FIG. 2 shows the case of the conventional example. Patent applicant: Showa Denko K.K. Patent attorney Hisashi Nakamura Figure 1

Claims (1)

[Claims] General formula (Ba_1_-_xSr_x)m(Ti_1_-
_y_-_zZr_yM_z)O_3 (However, M: Ta
and at least one of Nb, m: total molar ratio of A-site elements and B-site elements), and manganese oxide is converted to manganese dioxide (MnO_2) from 0.05 to 0.2. A ceramic composition for a reduction and reoxidation type semiconductor ceramic capacitor, characterized in that the material for a reduction and reoxidation type semiconductor ceramic capacitor is added in a weight% of 0.990≦m≦1.000.