JPS5946085B2 - Porcelain for semiconductor capacitors - Google Patents

Abstract

PURPOSE:To produce semiconductor capacitor with reduced thermal volume variation in such a manner that insulation layer is formed by diffusing Bi2 O3, MnO2 and Cu2O into granulated crystal of SrTiO3-Bi2O3-Nb2O5 or Ta2O5 system ceramic semiconductor.

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 (SrTiO3).

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

This barium titanate-based ceramic for semiconductor capacitors has an insulation resistance of 1011Ω-] and an effective dielectric constant of 50.00070.
．． Although a very large value of 000 can be obtained, the change in capacitance in the range of -30°C to +85°C is about ±40% with respect to 20°C, and the dielectric loss (tan δ) is also about 5 to 10%. The disadvantage is that it is large. 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 mainly made of strontium titanate were initially produced using strontium (SrTiO3), a small amount of manganese dioxide (MnO2), and silicon oxide (SiO2).
) etc. and sintered in a reducing atmosphere, the semiconductor porcelain is simply heat treated to oxidize the grain boundaries again, or manganese dioxide (MnO2), bismuth oxide (Bi2O3), etc. are thermally diffused into the grain boundaries. It was obtained by

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 (SrTiO3) for the purpose of improving the effective dielectric constant. For example, tantalum oxide (T
In addition to substances necessary for semiconductors such as a2O5), niobium oxide (Nb2O5), and tungsten oxide (WO3), the effective dielectric constant can be increased to 40 by adding zinc oxide (ZnO), rare earth oxides, etc. singly or in combination. ,000
Semiconductor ceramic capacitors with a dielectric loss of about 50,000 or less and a dielectric loss of 1% or less are now available, and efforts are being made to make them even more compact and high-performance. However, such a small and high-performance element has its own problems due to its high performance. One of the problems was that when applying a diffusion material, variations in the amount applied had 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. No, it wasn't enough. Furthermore, the insulation resistance could not be said to be sufficiently high in terms of balance with various properties, especially with respect to capacitance. The present invention was developed after various experiments,
This is due to the fact that variations in device characteristics caused by the above-mentioned diffusion process can be extremely reduced, and various characteristics can be improved, particularly the temperature change rate of capacitance and insulation resistance.

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

Examples> Strontium titanate (SrTiO3) is mixed with 0.1 to 2 mol% of niobium oxide (Nb2O3) and bismuth oxide (
Bi2O3) is added in a range of 0.1 to 5 mol%, mixed thoroughly, and then pressure-molded into a disc shape of 15 mφ x 0.7 m1t.

Thereafter, it is fired at 1370° C. to 1460° C. for 2 to 4 hours in an atmosphere consisting of 1% to 10% hydrogen and 99% to 900% 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 1.000°C to 1.200°C for about 2 hours. Silver electrodes are provided on both sides of the sintered body thus obtained. Table 1 Diffusion substances include copper oxide (
This is a summary of the results of the electrical characteristics of 20 various sheets when mixtures of various compositions consisting of Cu2O), bismuth oxide (Bi2O3), and manganese dioxide (MnO2) were applied to the above sintered body and diffused. .

However, the amount of bismuth oxide (Bi2O3) and niobium oxide (Nb2O5) added at this time was 0.2 mol% each.
, 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 11%.
The test was carried out at 00°C for 2 hours.

Note that the effective permittivity ε and dielectric loss Tanδ in the table are at a frequency of 1 KHz and 1 VA. The insulation resistance is 50VD.C. This value was measured after charging at a voltage of C for 30 seconds.

As is clear from this table, like composition points 1 to 3, C
It can be seen that when U2O, Bi2O3 or MnO2 is applied singly and diffused, the D value is very large, that is, the characteristics fluctuate greatly.

Furthermore, the insulation resistance r is small. Next, composition points 4, 5 and 6
is the best composition when two components are selected, and the variation in characteristics is smaller and the r value is larger than when one component is selected. Furthermore, at composition points 7 to 15 when three components are selected, MnO2 such as composition points 11 and 12
If it exceeds 20 mol%, the value of Tan δ is large and the fluctuation of properties is also slightly large, but at composition points 7, 8, 9, 10, 1
In No. 3, No. 14, and No. 15, the r value is particularly large compared to the case of one-component or two-component compositions, and the fluctuations in characteristics are extremely small. Incidentally, the characteristics of a capacitor can be expressed as the product of capacitance C and insulation resistance R.

This C-R product is a constant that does not depend on the shape of the capacitor, and if it is expressed by K, then K=CIR=εε0r.

Here, εo is the dielectric constant of vacuum. In other words, this K
A large value is one of the conditions for an excellent capacitor. In the example, when comparing the respective K values when using one-component, two-component, and three-component diffusing agents, the maximum K value is about 34 (MΩ・μF) for one component, and the maximum 289 (MΩ・μF) for two components. MΩ・μF), whereas for the three components, the composition points 7, 8, 9, 10, 13,
Looking at 14 and 15, the lowest value is 329 (MΩ・μF
), which is extremely large, at the maximum of about 496 (MΩ·μF).

From the above results, the blending composition of CU2O, Bi2O3 and MnO2 is as follows: Cu2O: 5-85 mol%, Bi2O3:
5 to 85 mol% and MnO2: 5 to 15 mol%.

FIG. 1 shows a typical example of the rate of change in capacitance with temperature when 20° C. is used as a reference.

In the figure, A is a barium titanate-based semiconductor capacitor, B is a case of porcelain using a diffusing agent consisting of two components of CU2O and Bi2O3 in the example, and C is an electrostatic charge of the porcelain of the present invention (composition point 8). This is a curve showing the rate of change in capacitance with temperature. As is clear from this figure, the CU2O of the present invention,
In porcelain using a diffusing agent consisting of the three components Bi2O3 and MnO2, the rate of change in capacitance with temperature is extremely small.
It has the advantage of expanding the operating temperature range.

As described above, according to the present invention, niobium oxide (Nb2O,) is added to strontium titanate (SrTiO3).
．． 1 to 2.0 mol%, and bismuth oxide (Bi2O3)
To the semiconductor porcelain which was added O~2.0 mol% and sintered,
Rather than simply diffusing copper oxide (Cu2O), bismuth oxide (Bi2O3), and manganese dioxide (MnO2) into the grain boundaries, Cu2O: 5 to 85 mol%, Bl2O3:
The ceramic for semiconductor capacitors, which is coated in the form of a composition consisting of 5 to 85 mol% MnO2 and 5 to 15 mol% MnO2, is diffused, and an insulating layer is provided at the grain boundaries. Not only is it small and easy to manufacture, but it also has excellent characteristics such as high insulation resistance and low temperature change rate of capacitance.

In the examples, niobium oxide (Nb2O, ) was used for the purpose of strontium titanate semiconductor, but tantalum oxide (Ta2O5) may also be used, and experimental results showed that tantalum oxide (Ta2O, ) was compared to niobium oxide (Nb2O5). Although there is a slight difference in that it is difficult to evaporate, this is on the order of almost negligible compared to the amount added.

For example, semiconductor porcelain is obtained by adding 0.2 mol% of niobium oxide (Nb2O,) to strontium titanate (SrTlO3) and firing it at 1400°C for 4 hours in an atmosphere consisting of 10% hydrogen and 90% nitrogen. Specific resistance is 0.5Ω
- The average crystal grain size is 12.5 μm, but when the amount of tantalum oxide (Ta2O,) added is 0.18 mol% and other conditions are the same, the specific resistance is 0.5 Ω.
Semiconductor porcelain with an average crystal grain size of 12.3 μm is obtained in one batch. Normally, niobium (Nb) and tantalum (Ta) are elements in the same group called vanadium group elements, and among them, these two elements have almost the same covalent bond radius (1.34 angstroms) due to lanthanoid contraction, so they can be used simultaneously. It is well known that these two pentavalent elements are produced and have almost the same chemical properties.The covalent bond radius (132 angstroms) of the Ti element in strontium titanate (SrTiO3) almost matches that of these two pentavalent elements.
Replacement is relatively easy, SrTlO3+Nb2O5
(or Ta2O,) → SrTll-δNbδ03 (or SrTil-δTaδ03) + δe-, free electrons are released, and strontium titanate (SrTiO3
) will be made into semiconductors.

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, it goes without saying that equivalent results can be obtained by replacing niobium oxide (Nb2O5) in the above embodiments with tantalum oxide (Ta2O5). Furthermore, in this example, the firing is not limited to an atmosphere consisting of 1 to 10% hydrogen and 99 to 90% nitrogen, and it goes without saying that any atmosphere that can sufficiently convert the sample into a semiconductor may be used.

Furthermore, although a silver electrode was used as the electrode, other known electrode materials may also be used.

[Brief explanation of the drawing]

The drawing is a graph showing the temperature change rate of capacitance, where A is a barium titanate semiconductor capacitor, B is a comparative example of porcelain using a diffusing agent consisting of CU2O and Bi2O3, and C is a porcelain of the present invention. The case is shown below.

Claims (1)

[Claims] 1 Strontium titanate (SrTiO_3) 99.
8-93.0 mol%, bismuth oxide (Bi_2O_3)
0.1-5.0 mol% and niobium oxide (Nb_2O_5
) or tantalum oxide (Ta_2O_5) 0.1-2.
Bismuth component,
Copper and manganese components are unevenly distributed, and its bismuth component,
Molar ratio of copper component and manganese component is 5-85:5-85
: Porcelain for semiconductor capacitors, characterized in that the number is 5 to 15.