JPS6029211B2 - Manufacturing method of semiconductor ceramic capacitor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor ceramic capacitor, and produces a semiconductor ceramic capacitor having a large capacity, low loss, a small temperature change rate of capacitance over a wide range, and a large resistance value. This is an attempt to provide a method that allows you to do so.

From the secondary to the ceramic capacitor, base Ti03 series porcelain or SITi03 series porcelain is used. These porcelains have a high yield rate and high insulation properties. When such porcelain is used in a capacitor, the capacitance depends on the dielectric constant of the porcelain, and the capacitance can be controlled to some extent by, for example, adjusting the thickness of the porcelain element or the area of its silver electrode-applied surface. It is something that can be done. The semiconductor ceramic capacitor of the present invention uses a semiconductor ceramic element having a relatively low resistivity, unlike the above-mentioned capacitor in which the ceramic element is an insulator.

To put it simply, a semiconductor ceramic capacitor is one in which a capacitive insulating layer is formed at grain boundaries on the normal outer or inner surface of a semiconductor ceramic. In such semiconductor ceramic capacitors, the former is called a surface layer type, and the latter is called a grain boundary layer type.

There are many types of semiconductor ceramic capacitors known so far, but most of them can be classified into one of the above two types. A surface layer type semiconductor ceramic capacitor has a thin insulating layer formed on the surface of its ceramic element, and utilizes the capacitance created by the thin insulating layer.

Structurally, most of the thickness of the ceramic element is occupied by the conductor, and the thin layer on the surface acts as a dielectric, making it possible to obtain a capacitor with a large capacity for low voltage use. On the other hand, grain boundary layer type semiconductor ceramic capacitors have a metal layer on the surface of the semiconductor ceramic element that acts as an insulator.
For example, the crystal grain boundary layer is made into an insulator by applying Cu or Mn oxide and heat treating it. Since such a grain boundary layer is made into a dielectric material, it has excellent withstand voltage and can obtain resistance values and capacitances suitable for high voltage applications. Whether the insulating layer is mainly formed on the surface of the semiconductor ceramic element or at the grain boundaries of the crystal is subtly influenced by the diffusion of oxygen into the element and the localization of impurities.

Furthermore, when semiconductor ceramics are used as capacitors, their characteristics are greatly influenced by the composition of the semiconductor ceramics and further by its subcomponents. Among the ceramic elements conventionally used in grain boundary type semiconductor ceramic capacitors are BaTjQ with oxides such as Sr, Bj, Zr, or Sn fixed therein.

This apparently has an effective dielectric constant of 40,000 to 70,000.
Although it is large, the capacitance temperature change rate is large and 20oo
Based on the standard, the maximum rate of change is around 50% within the temperature range of 12,500 to 85 pm. The dielectric loss (tan6) is also as large as 0.03 degrees. Also, SrTi
03 to which oxides such as Dy, Ce, Mn, Ta, W, Nb, Si or Bi are added, and even SrTi
There is one using semiconductor porcelain made of CaTj03 partially substituted with CaTj03. This SrTj03-based semiconductor ceramic has a capacitance temperature change rate of about 15%, which is significantly smaller than that of the Ti03-based bag mentioned above, and its dielectric loss (n6) is also 0.007~o. One as small as 03 has also been obtained. However, since the temperature required for sintering is as high as 140,000 or more, it is not common, and furthermore, its life characteristics are not very good. The present invention makes it possible to manufacture a ceramic capacitor that eliminates the above-mentioned drawbacks, and the resulting capacitor is a grain boundary layer type semiconductor ceramic capacitor that has a large apparent effective yield ratio and low dielectric loss. It has the characteristics of being small, in particular having a significantly small rate of change in capacitance over a wide temperature range, having a large resistance value and high breakdown voltage, and having good life characteristics.

The method of the present invention is characterized in that the Ti02 component is 5
0.20 to 53.22 mol% and Sr○ component is 49.
Sb, Ta, Nb, Bi, Si,
At least one selected from the metal element group consisting of AI, Ti, Ca, W, Ba, I, Gd, and Nd is added and fired in a neutral atmosphere to give a resistivity of 0.80-
The object of the present invention is to obtain a semiconductor ceramic element having an average crystal grain size of 5 to 100 mm, and to form electrodes on this element. Still further, the grain boundary layer of the semiconductor ceramic element obtained by sintering as described above is made into an insulator, and then electrodes are attached. According to this method, by changing the proportions of the components, the magnitude of the apparent charge rate and the rate of change in capacity with temperature can be freely selected, and the manufacturing thereof is also easy.

Furthermore, the ceramic element obtained by firing can be easily connected with a lead wire by soldering. Here we will discuss the reasons for determining the composition of semiconductor porcelain.

In the main components, when the Ti02 component increases, the power transfer rate decreases, the power transfer body loss and the capacitance temperature change rate increase, and the resistance of the ceramic element decreases. Furthermore, when the amount decreases, the dielectric constant decreases and the capacitance temperature change rate increases.
Therefore, the composition ratio of the main components is 50.20~
It is desirable that the content be within the range of 53.22 mol%. As the S component increases, the dielectric constant decreases, and the ceramic element becomes less likely to become a semiconductor.

Conversely, when the amount decreases, the effect of improving the rate of change in capacitance with temperature becomes poor. Therefore, it is desirable that the composition ratio of the main components be within the range of 46.78 to 49.80 mol%. Subcomponents Sb, Ta, N
b, Bi, Si, N, Ti, Ca, W, Ba, I, Gd
, and Nd are useful for increasing the crystal grain size and lowering the resistivity of the semiconductor ceramic element. Adding at least one of these ingredients,
Only by bonding in a neutral atmosphere can a semiconductor ceramic capacitor with a large dielectric constant and a small plexielectric loss (n6) be obtained. These components may be added as simple metals, or in the form of compounds such as oxides, chlorides, and carbonates. For components other than the above-mentioned components, the yield rate of semiconductor ceramics is low and it is difficult to obtain delicate ones. Furthermore, in the present invention, the reason why the firing atmosphere is neutral is to prevent explosiveness when additive components are added in the form of metals, reduce the resistivity of the porcelain, and then create a neutral atmosphere at the grain boundaries. This is to prevent the crystal particles themselves from becoming an insulator during the process of forming an insulator.

Note that the specific resistance value of the insulating layer formed at the grain boundaries is preferably 1070 or more. Furthermore, as a result of investigating the electrical characteristics of semiconductor ceramic capacitors in relation to the specific resistance and crystal grain size of the ceramic element, it was found that Sr.
When the specific resistance value of the Ti03-based semiconductor ceramic element is 0.80 or less and the average crystal grain size is within the range of 10 to 100 A, the capacitor capacity is large, especially the dielectric loss is small, and the capacitance temperature change rate is high. It has become clear that small capacitors can be obtained.

Note that the crystal grain size of the semiconductor ceramic element in the present invention is 1
Below 0r, the loss of the conductor is poor and the dielectric constant particularly decreases.
Furthermore, when the crystal grain size exceeds 100 μm, the mechanical strength of the ceramic element decreases, and insulation resistance and compaction loss worsen. If the resistivity is higher than 0.80 arc, the dielectric constant will be small and the capacitance temperature change rate will be large, which is not preferable.
In particular, a ceramic element with a resistivity higher than 0.80 becomes extremely unstable during the process of converting grain boundaries into an insulator, making mass production difficult. When the specific resistance is within the range of the present invention and the crystal grain size is outside the range of the present invention, or when there is an inverse relationship, the dielectric constant deteriorates. Next, the method of the present invention will be explained based on examples.

First, TiO2 and SrC, which are industrial raw materials with a purity of 98% or more,
03 and an Sb component having a purity of 99.99% or more were prepared and mixed to have the composition ratios shown in the table below.

Note that the types of both Ti and Sr are not particularly limited as long as they become oxides during the firing process. Raw material powders prepared to have a predetermined composition ratio were placed in a urethane-lined pot, wet-mixed using a urethane pole, and then water in the mixture was evaporated.

Then, applying a force of about 700k9/earth, it was molded into a disk shape with a diameter of 15 ribs and a thickness of 0.8 ribs, and this molded body was heated at 1300 to 140 pi0 in an atmosphere consisting of nitrogen or argon.
It was held and fired for 2 hours. Of course, an inert gas other than nitrogen or argon may be used to create a neutral atmosphere. The firing was carried out in an alumina combustion tube using an SIC heating element. On the surface of the obtained semiconductor ceramic element, Cu
At least one of No. 20, Bi203, PQ04, Mn02, etc. was applied as a diffusing substance in 1 to 3 layers, and was heat-treated at 1100 to 1300 CC in the atmosphere to diffuse it. The thus obtained ceramic element was examined using an X-ray microanalyzer, and it was confirmed that ions of the diffusing substance were present at the grain boundaries. Further, electrodes were formed on both sides of the semiconductor ceramic element. The specific resistance value of the semiconductor ceramic element was measured by applying ohmic electrode material made of ln-Ga to both surfaces of the obtained illuminated ceramic element.

The grain size measurement method used to classify the crystal grain size is as follows.

The surface of the semiconductor ceramic element was polished with diamond paste to make it mirror-like. This was treated with an etching solution prepared by adding 5 cc of 5% hydrofluoric acid to 95 cc of 8% hydrochloric acid, and then the sample surface was observed under a microscope. If the area of the field of view of the microscope is S and the number N of crystal grains present therein is counted, the average diameter r of the grains can be obtained from the following formula. In the present invention, the crystal grains were counted in the field of view 5 of the microscope at a magnification of 500, and the average particle diameter was determined from the number of crystal grains.

In the method of the present invention, the particle size of the porcelain element is determined by additives and firing conditions, and the reproducibility is extremely good. Therefore, when actually manufacturing, a small number of samples are extracted for each lot. , it is enough to make a judgment just by identifying it.

On the other hand, for comparison, a ceramic element was fired in air (Sample 12). The table below summarizes the measurement results for each sample.

In this table, dielectric constant (g) and dielectric loss (n)
6) are values measured at a temperature of 20 qo and a frequency of IKHz. Also, the capacitance temperature change rate is the dielectric constant change rate, that is, 20°C is the standard, -25°C and 85°C.
Evaluation was made based on the rate of change in value when . As is clear from the above table, Samples 1 to 9 were obtained by changing only the composition ratio of the main components, and from Samples 2 to 8, the samples prepared by the method of the present invention were superior in yield rate and yield loss. In particular, the capacitance temperature change rate is small, and the characteristics are good.

In particular, sample 5 is excellent, and its insulation resistance value is extremely large, 7×1 and Q-skin when a DC voltage of 50 V is applied. In addition, the capacitance and conductor loss change little with respect to the application of either DC or AC voltage, and the characteristics are stable. Samples 10 to 12 are examples when the firing atmosphere was changed, but sample 1 was fired in a hydrogen atmosphere.
Sample No. 1 and Sample No. 12 fired in air are inferior to Sample No. 10 in terms of characteristics.

Moreover, sample 10 is almost the same as sample 5, and sample 1
As is clear from comparison with Nos. 1 and 12, the firing atmosphere is preferably neutral, and is undesirably reducing or oxidizing. Samples 13 to 16 are examples in which the firing temperature was changed with the same material composition.
It was fired at a temperature of qo.

Samples 17 to 20 were fired at a firing temperature of 1380 oo and only the holding time was changed, and samples 17 to 20 were held for 4, 6, 8, and 1 field hours, respectively. From this, it can be seen that Samples 13 to 15 and 17 and 18, which are within the scope of the present invention, have excellent characteristics. Generally, the larger the sintered grain size, the higher the capacity, but if it becomes extremely large, the crystallinity will deteriorate, and the diffusing agent will diffuse deep into the grain, resulting in a small capacity.Also, due to the poor crystallinity, complete valence compensation will not be achieved. Therefore, it is considered that the specific resistance is small and tan6 is large. On the other hand, possible reasons for the increase in the resistivity of atmosphere-fired elements include the segregation of valence control agents at grain boundaries and the solid solution of extremely small amounts of impurities inside the grains, resulting in a decrease in capacity and increase in tan6. considered to be a thing.

As can be seen from the examples, excellent capacitor characteristics can be obtained by simultaneously satisfying the particle size and specific resistance requirements of the present application.
Further details are shown in FIGS. 1 and 2. These figures show that the main components are Ti02 (51.50 mol%) and S (48.
50 mol%) and the subcomponent force Sb203 (0.142
Parts by weight: values based on 100 parts by weight of the main components, the same applies hereinafter), Ta205 (0.057 parts by weight), and NQ05 (0.057 parts by weight).
085 parts by weight) and Bi203 (0.230 parts by weight). Figure 1 shows the relationship between crystal grain size and dielectric constant.If we look at the dielectric constant from now on, we will find that the grain size is too small,
Or, if it is large, it is recognized that the yield rate decreases. FIG. 2 shows the relationship between resistivity and dielectric constant of a semiconductor ceramic element. From this, it can be seen that as the specific resistance increases, the dielectric constant tends to decrease. Sample 21~
No. 27 is mainly a product with different additive components, but even if the types, combinations, and forms of additive components (single substances or types of compounds) are different, as long as they are within the scope of this Act, they can be used as semiconductor ceramic capacitors. It can be seen that it has desirable characteristics. In addition, in sample 26, an amount of CaC03 and T was added to the Ti02-S system to form a CaTi03 system.
It can be seen that by adding i02, the capacitance temperature change rate becomes smaller. However, in this case, a tendency for the dielectric constant to decrease slightly was observed. As described above, according to the method of the present invention, it is possible to manufacture a semiconductor ceramic capacitor, particularly a semiconductor ceramic element passed through the capacitor.

The resulting capacitor also has excellent characteristics, and even through mass production, it is possible to obtain a capacitor with stable characteristics.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the crystal grain size and dielectric constant of a semiconductor ceramic element, and FIG. 2 is a diagram similarly showing the relationship between specific resistance and dielectric constant. Figure 1 Figure 2

Claims (1)

[Claims] 1 Sb, T as subcomponents to 100 parts by weight of the main component consisting of 50.20 to 53.22 mol% of TiO_2 component and 49.80 to 46.78 mol% of SrO component.
a, Nb, Bi, Si, Al, Ti, Ca, W, Ba,
At least one metal selected from the metal element group consisting of La, Gd, and Nd or a compound that becomes an oxide when fired is added, and fired in a neutral atmosphere to achieve a resistivity of 0.8 Ω-cm or less. , the average crystal grain size is 15-10
1. A method for manufacturing a semiconductor ceramic capacitor, which comprises obtaining a semiconductor ceramic element having a particle diameter within the range of 0μ, and further forming an electrode on the element after converting the grain boundary layer of the semiconductor ceramic element into an insulator. 2. Sb, Ta, Nb, Bi, Si, Al, Ti
, Ca, W, Ba, La, Gd, and Nd, or a compound that becomes an oxide upon firing is added, and fired in a neutral atmosphere to reduce the specific resistance. Obtaining a semiconductor ceramic element having a crystal grain size of 0.8 Ω-cm or less and having an average crystal grain size within the range of 5 to 100 μm, and further converting the grain boundary layer of this semiconductor ceramic element into an insulator,
A method for manufacturing a semiconductor ceramic capacitor, further comprising attaching electrodes.