JPS6258127B2 - - Google Patents

Description

[Detailed description of the invention]

This invention relates to a barium titanate-based reduced and reoxidized semiconductor capacitor ceramic composition. Traditionally, semiconductor capacitors include grain boundary insulated types in which Cu, Bi, Mn, etc. are diffused in the grain boundaries of semiconductor porcelain, surface weir layer types that utilize the surface layer of semiconductor porcelain, and reduction and reoxidation types. something is known. Among these, grain boundary insulated semiconductor capacitors include BaTiO ₃ -based and SrTiO ₃ -based materials.
In recent years, the SrTiO ₃ type, which has excellent temperature characteristics and bias characteristics, has become mainstream. In addition, this type of capacitor has other advantages such as little variation in characteristics even when the type of electrode changes, and excellent reliability. However, on the other hand, the disadvantages include that the process is complicated, which increases the cost, that the breakdown voltage is low, and that the area capacitance cannot be increased. In addition, surface weir layer type semiconductor capacitors can obtain a relatively large area capacitance, but the breakdown voltage and
Low insulation resistance limits the range of use. Furthermore, reduction and reoxidation semiconductor capacitors are made by heat-treating dielectric ceramic in a reducing atmosphere to make it a semiconductor.
It is then obtained by performing heat treatment in an oxidizing atmosphere to form a dielectric layer on the surface, and then providing electrodes. Therefore, the electrical characteristics of this type of capacitor, such as capacitance, insulation resistance, breakdown voltage, and capacitance temperature characteristics, are largely influenced by the state of formation of the dielectric layer. Many reduction-reoxidation semiconductor capacitors have been introduced in patent publications and literature, and have also been put into practical use, but in recent years there has been a strong demand for smaller capacitors with larger capacities.
There is a demand for materials with higher areal capacitance (0.7 μF/cm ² or more). However, in order to increase the areal capacity, if the permittivity of the dielectric ceramics is the same, the reoxidation layer (dielectric layer) on the surface of the semiconductor ceramic must be thin, and conversely the breakdown voltage and insulation resistance This will lead to a decrease in In order to achieve a smaller size and larger capacity, it is necessary not only to have a large area capacitance but also to have a high breakdown voltage and insulation resistance, and for this purpose, the following conditions must be satisfied. The dielectric constant of dielectric porcelain is large. Porcelain is dense and the crystal grain size is uniform and small. High reduction and reoxidation rates. Conventionally, reduction and reoxidation semiconductor capacitors have
Composition systems in which Mn oxide is added to a solid solution such as BaTiO ₃ -La ₂ O ₃ -TiO ₂ system are known. However, when the crystal grain size of these compositions is small, the dielectric constant becomes as small as about 8,000 to 10,000. Also, the dielectric constant
If you try to make it more than 12,000, the crystal grain size becomes larger than 3μm, and the areal capacitance becomes 0.7μF/
When the temperature exceeds cm ² , the breakdown voltage and insulation resistance are extremely reduced, making it impossible to put it to practical use. As a result of research on various barium titanate-based compositions, the inventor discovered a reduction-reoxidation type semiconductor capacitor that has a high dielectric constant, is dense in porcelain, has a finely uniform crystal grain size, and is easy to reduce and reoxidize. As a result, they were able to make capacitors smaller and larger in capacity. That is, this invention combines manganese oxide with Mn in the main components including barium titanate (BaTiO ₃ ), cerium oxide (CeO ₂ ), zirconium oxide (ZrO ₂ ), and if necessary neodymium oxide (Nd ₂ O ₃ ). The content is calculated as 0.01 to 0.4% by weight. This composition is processed and constructed as a semiconductor capacitor as follows. That is, the raw material composition is prepared and mixed, this mixture is molded and fired in an oxidizing atmosphere, then heat treated in a reducing atmosphere to produce semiconductor porcelain, and then heat treated in an oxidizing atmosphere to form a surface of the semiconductor porcelain. A semiconductor capacitor is constructed by forming a thin dielectric layer and adding electrodes to the surface. The reduction and reoxidation type semiconductor capacitor ceramic composition according to the present invention mainly uses cerium oxide (CeO ₂ ) and zirconium oxide (ZrO ₂ ) as shifters of the Curie point, and Nd ₂ O ₃ , La ₂ O 2 The dielectric constant at the Kyrie point is larger than 15,000 compared to conventional examples using ₃ etc. as a shifter at the Kyrie point, and although the dielectric constant is 15,000 or more, the crystal grain size is small at 1.0 to 1.5 μm or less. We fully meet the requirements for small, large-capacity reduction-reoxidation type semiconductor capacitors, such as uniform crystal grain size, good sinterability, dense porcelain, and ease of reduction and reoxidation. It's satisfying. The present invention will be described in detail below using examples. When preparing samples, BaTiO ₃ , CeO ₂ , Nd ₂ O ₃ ,
Each raw material of ZrO ₂ and MnCO ₃ was weighed, and each weighed raw material was put into a polypot and mixed with an organic binder such as vinyl acetate for 16 hours. After mixing, the mixture was dehydrated and dried, and passed through a 50-mesh sieve to size the mixture. then
It was molded into a disk with a diameter of 10 mm and a thickness of 0.5 mm under a pressure of 1000 Kg/cm ² and fired in air at 1300 to 1360° C. for 2 hours. 1000~1200 dielectric porcelain obtained in this way
It was heat-treated at ℃ for 2 hours in a reducing atmosphere to obtain semiconductor porcelain. This semiconductor porcelain was heat-treated at 850 to 1000°C for 2 hours in air, an oxidizing atmosphere.
A thin dielectric layer was formed on the surface of semiconductor ceramic. Silver paste is then applied to the surface of the semiconductor porcelain and baked at 700-850℃ for 30 minutes to form electrodes.
A reduced and reoxidized semiconductor capacitor was obtained. Regarding the capacitor created in this way,
Average grain size of porcelain, dielectric constant, capacitance per unit area [C (μF/cm ² )], dielectric loss [tanδ (%)],
Insulation resistance [IR (Ω)] and breakdown voltage [Vb (V)] were measured, and the results are shown in Table 1. Note that the capacitance and dielectric loss are values measured at 0.1Vr.ms and 1KHz. Since the capacity changes depending on the reduction temperature and reoxidation temperature, the reduction temperature is set so that the porcelain specific resistance after reduction is constant, and the reoxidation temperature is set to increase the areal capacity to 0.7μF/
cm ² and evaluated using other electrical properties to facilitate comparison. Insulation resistance was measured by applying 12VD.C for 1 minute. For the breakdown voltage, a DC boost breakdown method was used. The dielectric constant was measured at 1.0Vr.ms and 1KHz, and the measurement temperature was set at 20°C. In addition, those marked with * in Table 1 are outside the scope of this invention, and the others are within the scope of this invention.

[Table] As is clear from Table 1, the reduced and reoxidized semiconductor capacitor ceramic composition of the present invention can provide a semiconductor capacitor with extremely excellent electrical characteristics. That is, although the capacitance per unit area is as large as 0.7 μF/cm ² , it exhibits excellent characteristics such as a breakdown voltage of 400 V or more, an insulation resistance of 10 ¹⁰ Ω or more, and a dielectric loss of 3.0% or less. It was also confirmed that the variation in breakdown voltage values was small. In the conventional BaTiO ₃ -La ₂ O ₃ -TiO ₂ system, if we try to obtain a property with an insulation resistance of 10 ¹⁰ , the areal capacitance is at most about 0.4 to 0.5 μF/cm ² and the breakdown voltage is also low. However, according to this invention, it is possible to obtain an areal capacitance of 0.7 μF/cm ² and a breakdown voltage of over 400 V, which is a significant improvement in the ability to achieve a compact, large capacitance ratio and high withstand voltage of the capacitor. It can be said that it is excellent. As mentioned above, the excellent characteristics obtained in this invention are due to the fact that, as is clear from Table 1, the average crystal grain size of the porcelain is uniform at 1.0 to 1.5 μm, despite the large dielectric constant of 12,000 or more. In addition, as a result of mirror-polishing the cross section of the porcelain and observing the amount and distribution of pores inside, it was found that the porcelain is denser than conventional porcelain, and it is easy to reduce and reoxidize. , etc. are cited as reasons for this. The reason why the scope of the composition is limited in this invention is as follows. (1) If CeO ₂ is less than 1.0 mol%, the dielectric constant at room temperature will be low because there will be no movement of the Curie point, and the sinterability will be poor, resulting in an areal capacitance of 0.7 μF/cm ²
As the value increases, both IR and Vb become worse, and tanδ also becomes worse. Moreover, if CeO ₂ exceeds 6.0 mol %, the dielectric constant becomes low and both IR and Vb deteriorate. (2) If ZrO ₂ is less than 1.0 mol%, sinterability deteriorates, tan δ increases and Vb decreases. Moreover, when ZrO ₂ exceeds 15.0 mol %, the dielectric constant decreases and fusion of porcelain occurs. (3) The composition range of BaTiO ₃ is CeO ₂ , ZrO ₂ (and
Nd ₂ O ₃ ), but as is clear from the samples outside the scope of this invention (sample numbers 11 and 14), both have low dielectric constants and low IR and Vb. (4) Addition of manganese oxide is effective in improving IR, improving Vb, and further improving tanδ, but if manganese oxide is less than 0.01% by weight in terms of Mn, there is no effect of adding manganese oxide, and 0.4% by weight If the dielectric constant is exceeded, the dielectric constant of the ceramic decreases, and if the dielectric layer is made thinner to increase the areal capacitance, IR and Vb decrease. (5) When Nd ₂ O ₃ coexists in the main component, the sinterability is further improved, but when the content exceeds 0.3 mol %, the crystal grain size of the porcelain increases and Vb decreases. In addition, in this invention, instead of ZrO ₂
Contains TiO ₂ or a part of ZrO ₂
It was confirmed that substitution with TiO ₂ had similar effects. Also, La ₂ O ₃ instead of Nd ₂ O ₃ ,
Contains Pr ₂ O ₃ or a part of Nd ₂ O ₃
It was confirmed that the same effect can be obtained even when the material is substituted with at least one of La ₂ O ₃ and Pr ₂ O ₃ . As is clear from the above description, according to the present invention, the capacitor is characterized by an extremely large areal capacitance than ever before, and also has characteristics such as high insulation resistance and breakdown voltage. It has the effect of being able to provide the following.

Claims (1)

[Claims] 1. Barium titanate (BaTiO ₃ ) is
The main components are 79.0 to 98.0 mol%, 1.0 to 6.0 cerium oxide (CeO ₂ ), and 1.0 to 15.0 zirconium oxide (ZrO ₂ ), with 0.01 to 0.4 weight % manganese oxide added in terms of Mn. A reduced and reoxidized semiconductor capacitor ceramic composition. 2 Barium titanate (BaTiO ₃ )
More than 78.5 mol% and less than 98.0 mol% Cerium oxide (CeO ₂ ) 1.0 to 6.0 mol% Neodymium oxide (Nd ₂ O ₃ ) less than 0.5 mol% Zirconium oxide (ZrO ₂ ) 1.0 to 15.0 mol% A reduction and reoxidation semiconductor capacitor ceramic composition containing manganese oxide as a main component in an amount of 0.01 to 0.4% by weight in terms of Mn.