JPS5827649B2 - Porcelain for semiconductor capacitors - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ceramic for a semiconductor capacitor obtained by providing a highly insulating layer at the grain boundaries of a semiconductor ceramic mainly composed of strontium titanate (SrTi03).

BACKGROUND ART Barium titanate ceramics for semiconductor capacitors are known as capacitor materials obtained by insulating the grain boundaries of semiconductor ceramics.

However, the insulation resistance is 10"Ω-α, the effective permittivity is 50
A disadvantage of this barium titanate ceramic for semiconductor capacitors, which can obtain very large values of 000 to 70,000, is that the capacitance changes by about ±40% in the range of -30°C to +85°C, with 20°C as the standard. In addition, the dielectric loss (tan δ) may be as large as about 5 to 10%.

Therefore, in recent years, semiconductor ceramic capacitors have been developed that are mainly made of strontium titanate and have a particularly low temperature change rate of capacitance.

Semiconductor ceramic capacitors using strontium titanate as a living body were initially developed using strontium titanate (SrTi03).
) with a small amount of manganese dioxide (Mn 02 ), silicon oxide (Si02), etc. added and sintered in a reducing atmosphere. 02), bismuth oxide (B
1203) etc., by thermally diffusing them into grain boundaries.

These characteristics include that the rate of change in capacitance with temperature is smaller than that of barium titanate-based materials, and the value of dielectric loss (tan δ) is also small.

On the other hand, the drawback was that the effective dielectric constant was extremely small compared to barium titanate.

Therefore, several impurities have been proposed to be added to strontium titanate (SrTi03) for the purpose of improving the effective dielectric constant.

For example, tantalum oxide (Ta2o5), niobium oxide (
Nb20. ), by adding zinc oxide (ZnO), rare earth oxides, etc. alone or in combination in addition to the substances necessary for semiconductor formation such as tungsten oxide (WO3), an effective dielectric constant of 40,000 to 50,000 can be achieved. Semiconductor ceramic capacitors with a dielectric loss of 1% or less have become available, and efforts are being made to make them even smaller and higher in performance.

However, such a small and high-performance element has some problems because of its high performance.

One of the drawbacks is that when applying a diffusion material, variations in the amount of coating have a large effect on the characteristics, making process control extremely difficult.

Furthermore, efforts are being made to improve the performance of electrical properties, but in particular, the change in capacitance due to changes in ambient temperature has been reduced compared to barium titanate. , it's just not enough.

The present invention, based on various experiments, has been developed to extremely minimize variations in device characteristics due to the above-mentioned diffusion process, and further to minimize changes in dielectric constant with temperature.

Hereinafter, the present invention will be described in detail based on Examples.

Example Strontium titanate (SrTi03), bismuth oxide (B1203) 0.1-2 mol% and niobium oxide (
After adding Nb205) in a range of 0.1 to 2 mol% and thoroughly mixing, 15m2I! Pressure mold into a disc shape of φX0.7m1Lt.

Thereafter, it is fired at 1370'C to 14600G for 2 to 4 hours in an atmosphere consisting of 1 to 10% hydrogen and 99 to 90% nitrogen.

Thereafter, a diffusion substance is applied to one side of the sintered body using a known suitable binder (for example, polyvinyl alcohol), and heat treated at 1050° C. to 12000° C. for about 2 hours.

Silver electrodes are provided on both sides of the sintered body thus obtained.

Table 1 shows the average values of the electrical characteristics of 20 various sheets when a mixture of various compositions consisting of bismuth oxide (Bi203) and copper oxide (Cu20) as a diffusion substance was applied to the above sintered body and diffused. shows.

However, the amounts of bismuth oxide (Bi203) and niobium oxide (N b 205 ) added at this time were each 0.
2 mol%, and the firing was performed at a temperature of 1400° C. for 4 hours, the atmospheric conditions were 10% hydrogen and 90% nitrogen, and the heat treatment was performed at a temperature of 1100° C. for 2 hours.

The effective dielectric constant ε and dielectric loss tan δ in the table are values measured at a frequency of IKHz, IVA, C, and the insulation resistance is a value measured after charging at a voltage of 50 VD, C for 30 seconds.

Further, FIG. 1 illustrates the characteristics of the above-mentioned sample.

In the figure, all the samples are included in the shaded area, the curve at the upper limit of the area shows the maximum value of the sample, and the curve at the lower limit shows the minimum value of the sample.

As is clear from these tables and figures, the characteristics of the sample are better when a combination of copper oxide (Cu20) or bismuth oxide (Bi203) is applied and diffused than when they are applied and diffused. Not only is there an improvement, but it is also recognized that the variation is small.

In addition, FIG. 2 shows that the sintered body of the above example was used, and the applied amount of the diffusion substance was 0, 3 m91crl, and 0.5, respectively.
The characteristic values are shown when m51/ctit and 1.0 m47/ctrl are used, and curves a, b, and C in the figure are characteristic curves corresponding to the respective coating amounts.

As is clear from this figure, the effect of the coating amount on the electrical characteristics is smaller for the combination of copper oxide (Cu 20 ) or bismuth oxide (Bi2oa) than for single coating. Waru.

Furthermore, it is clear from this figure that the variation in characteristics in FIG. 1 is due to the difference in coating amount.

Next, FIG. 3 shows the rate of change in capacitance at −25° C. and +85° C. with 20° C. as a reference in the ceramic for semiconductor capacitor constructed using the sintered body of the above example.

As is clear from this figure, bismuth oxide (B 120
It is recognized that the temperature dependence of the dielectric constant is extremely small in the ranges of 5 to 95 mol% and 95 to 5 mol% of copper oxide (Cu20) and copper oxide (Cu20), respectively.

In particular, at a composition point of Cu2020 mol% and Bi20380 mol%, it is 3.8% at -25°C, -4% at +85°C,
It showed an extremely small value of 3%.

In addition, by adding bismuth oxide (Bi203) to strontium titanate (SrTi03), the growth of microcrystalline particles in the sintered body is promoted and uniform, compared to the case where bismuth oxide (Bi203) is not added. The variation in properties is reduced, and in particular, the effective dielectric constant is improved.

Table 2 shows typical examples of the differences in the properties of the above three materials, and (4) in the table shows strontium titanate (S rT
iO3) with 1 mol% of niobium oxide (Nb205) added and sintered under the same conditions as above, and 80 mol% of bismuth oxide (B1203) and copper oxide (Cu20).
A composition consisting of 20 mol% was applied and diffused in the same manner as in the above example.The porcelain (CB) was made of strontium titanate (SrTi03) and niobium oxide (Nb20.0).
．． 1 mol%, bismuth oxide (B l 203) 1.5
Porcelain treated under the same conditions as A is shown below.

Thus, it can be said that the effect of the present invention is further enhanced by adding bismuth oxide (8120 g) to strontium titanate (SrTi03) in advance.

As described above, according to the present invention, strontium titanate (SrTi03) contains at least 0.1 to 2 mol% of niobium oxide (Nb205) necessary for semiconductor formation, and further contains at least 0.1 mol% of bismuth oxide (Bi203). ~
Bismuth oxide (B I 2
03) or copper oxide (Cu 20 ) is not simply diffused into the grain boundaries, but by applying and diffusing them in the form of a composition consisting of 5 to 95 mol% and 95 to 5 mol%, respectively. It is possible to provide an extremely excellent ceramic for semiconductor capacitors that has less manufacturing variation than ever before and has a small rate of change in dielectric constant with temperature, and has enormous industrial value.

Although silver electrodes were used in the examples, it goes without saying that other known electrode materials may be used.

Furthermore, it is well known that the calcination is not limited to an atmosphere consisting of 1 to io% hydrogen and 99 to 90% nitrogen, and any atmosphere that can sufficiently convert the sample into a semiconductor is sufficient.

Furthermore, tantalum oxide (T a 20
5) may be used, and experimental results show that niobium oxide (Nb2
0. ), but this is on the order of almost negligible compared to the amount added.

For example, the ratio of semiconductor porcelain obtained by adding 0.2 mol% of niobium oxide (Nb205) to strontium titanate (SrTi03) and firing it at 1400°C for 4 hours in an atmosphere consisting of 10% hydrogen and 90% nitrogen. Resistance is 0.5Ω
-α and the average grain size is 12.5 μm, while the amount of tantalum oxide (Ta 20s) added is 0.1 μm.
8 mol% and other conditions are the same, the specific resistance is 0.
A semiconductor porcelain having a resistance of 5Ω and an average crystal grain size of 12.3 μm is obtained.

Normally, niobium (Nb) and tantalum (Ta) are elements in the same group called vanadium group elements, and these two elements have almost the same covalent bond radius (1.34 angstroms) due to lanthanoid contraction. Therefore, it is well known that they are produced at the same time and have almost the same chemical properties.

These two pentavalent elements are strontium titanate (Sr
Since it almost matches the covalent bond radius (1.32 angstroms) of the Ti element in 5rTi03+Nb205 (or Ta203), substitution is relatively easy.
) → 5rTi1-δNbδ03 (or 5rTi1-δTaδ03) + δe- Free electrons are released as strontium titanate (
SrTi03) is made into a semiconductor.

Here, δ represents the number of atoms of the substituted Nb (or Ta) element, and e- represents an electron.

Such a semiconductor manufacturing method is generally called a valence control method.

Therefore, niobium oxide (Nb20
It goes without saying that equivalent results can be obtained by replacing ) with tantalum oxide (T a 205).

[Brief explanation of the drawing]

FIG. 1A is a diagram showing the relationship between the dielectric constant and dielectric loss of the ceramic for semiconductor capacitors and the composition of the diffusing material in an example of the present invention, and FIG. 1B is a diagram showing the relationship between the insulation resistance and the composition of the diffusing material of the ceramic for semiconductor capacitors. Figure 2A is a diagram showing the relationship between the dielectric constant and dielectric loss and the composition of the diffusive material when the coating amount of the diffusing material in the embodiment of the present invention is taken as a parameter.
Figure B is a diagram showing the relationship between insulation resistance and diffusion material composition when the amount of diffusion material applied in the embodiment of the present invention is taken as a parameter;
FIG. 3 is a diagram showing the relationship between the composition of the diffusive material and the rate of change of capacitance with temperature in an example of the present invention.

Claims (1)

[Claims] 1 Strontium titanate (5rTi03) 99.8
~96.0 mol% bismuth oxide (B l 203 )
Bismuth components and copper components are unevenly distributed in the grain boundaries of polycrystalline semiconductor porcelain consisting of 0.1 to 2 mol% and 0.1 to 2 mol% of niobium oxide (Nb20.) or tantalum oxide (Ta205), and the bismuth component The molar ratio of copper and copper components is 5 to 9.
5295-5. Porcelain for semiconductor capacitors, characterized in that