JPH0153496B2 - - Google Patents

Description

[Detailed description of the invention]

Industrial Application Field The present invention has a theoretical density ratio of 99% TD (Theoretical Density), which is the ratio of the actual density to the density when there are no pores inside the ceramic (theoretical density).
The present invention relates to a method for manufacturing a reduction and reoxidation type semiconductor ceramic capacitor that can produce high-density ceramics in the above case. Structure of conventional example and its problems The conventional manufacturing method for reducing and reoxidizing semiconductor ceramic capacitors is to first make dielectric ceramic by firing in the air, and then process it in a high-temperature reducing atmosphere at 1 to 2 atmospheres to convert the entire ceramic into a semiconductor. It requires a three-step heat treatment to convert the porcelain into an insulator, and then re-oxidize the surface of the porcelain to make it an insulator. Since this reduction/reoxidation type semiconductor ceramic capacitor utilizes a surface layer of about 1 to 40 μm, its electrical characteristics are significantly influenced by internal pressure pores (vacancies existing inside the ceramic). Conventional method and pore distribution (distribution of intrinsic pores)
The theoretical density ratio
The limit was 94% TD to 98% TD, and 99% TD or higher was nearly impossible. Therefore, the withstand voltage characteristics, dielectric loss, etc. were poor. In addition, dielectric porcelain fired in an oxidizing atmosphere is hot isostatically pressed (HIP) in reducing powder.
However, there is a method in which semiconducting porcelain and dense ceramics are obtained at the same time and then subjected to reoxidation treatment, but it is extremely difficult to control the semiconducting process using reducing powder, resulting in poor quality stability and product yield. (Hot isostatic press reference: Published by Industrial Technology Center, Ceramics Materials Technology Collection P684~
P688). Purpose of the invention The present invention eliminates the conventional drawbacks and provides a maximum pore diameter of 3 μm.
The object of the present invention is to provide a method for manufacturing a reduction and reoxidation type semiconductor ceramic capacitor that provides poreless ceramics with a diameter of less than m, high withstand voltage characteristics, low dielectric loss, high quality stability, and excellent yield. Structure of the Invention In order to achieve the above object, the present invention hot isostatically presses semiconductor porcelain obtained by heat treatment in a reducing atmosphere, and further subjects the surface of this semiconductor porcelain to reoxidation treatment, thereby achieving high durability. We were able to obtain a reduction-reoxidation type semiconductor ceramic capacitor that has excellent voltage characteristics, low dielectric loss, high quality stability, and excellent yield. DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described based on the drawings. Example 1 In the sample preparation process, the semiconductor ceramic composition was as follows:
Commercially available industrial raw material BaCO ₃ powder (purity 99.9% or more),
TiO ₂ powder (purity 99.9% or more), Nd ₂ O ₃ powder (purity
99.9% or more) and commercially available reagent grade MnO ₂ powder to the composition ratio shown in Table 1, wet-mixed using a urethane-lined pot to prevent contamination with impurities, and dried. Temporary firing was performed at a temperature of 4 hours. This calcined product was wet-pulverized, dried, mixed with an aqueous polyvinyl alcohol solution as a binder, and sized into 32 mesh passes. This sized powder was molded into a disk shape with a diameter of 13 mm and a thickness of 0.5 mm using a pressure of 1 t/cm ² , and these molded bodies were fired in air at a temperature of 1300°C for 2 hours, and then 90% _N2 −10% _H2
Semiconductor porcelain was obtained at 1100°C in a mixed gas. Table 1 Semiconductor porcelain composition (mol %) BaO Nd ₂ O ₃ TiO ₂ MnO ₂ 48.65 0.68 50.37 0.3 Thereafter, the semiconductor porcelain was hot isostatically pressed in Ar. At this time, the relationship between the hot isostatic pressing conditions, the theoretical density ratio of the porcelain, and the average grain size was determined as follows.
It is shown in Fig. 2. The thus obtained reduced and reoxidized semiconductor porcelain was subjected to pressure treatment in air at a temperature of 900°C.
Silver electrodes are baked on both sides of this reduction and reoxidation type semiconductor porcelain to make a capacitor element, and its capacitance per unit area C (measurement frequency 1KHz) and dielectric loss tanδ (1K
Hz), insulation resistance IR (applied voltage during measurement: 50V DC),
Breakdown voltage Vb and Vickers hardness Hv (Kg/mm ² ) when a load of 500 g was applied for 15 seconds were measured. The results are shown in Table 2. Here, comparative sample No. 8 is made from a sample that is not subjected to hot isostatic pressing. Samples No. 1 to No. 5 according to the present invention were compared to sample No. 8.
Compared to the previous model, excellent capacitor characteristics can be obtained, such as an increase in IR of about 40%, a rise in Vb of about 55%, a rise in C of about 15%, and a decrease in tanδ of about 40%. Sample No. 6 is a comparative example outside the invention, and has characteristics inferior to those of the present invention.

【table】

[Table] Under hot isostatic pressing conditions, as shown in Figure 1, the pressure effect decreases rapidly below 1000℃, and the temperature effect decreases below 300 atm. ) cannot be obtained. In addition, as shown in Figure 2, the average grain size depends on the hot isostatic pressing temperature and does not depend much on the hot isostatic pressing pressure. ), grains grow rapidly and, as can be seen from the results of sample No. 7 in Table 2, the capacitor characteristics deteriorate. That is, if the firing temperature is T°C, then the hot isostatic pressing temperature is T-300°C, as shown in Figure 4.
If it is less than T.degree. C., no increase in porcelain density will be observed, and if it exceeds T.degree. C., grain growth will be promoted and foreign phase precipitation will occur, resulting in deterioration of capacitor characteristics. Further, when the hot isostatic pressing pressure is less than 300 atm, no increase in the density of the porcelain is observed. FIG. 3 shows the relationship between the average crystal grain size of semiconductor porcelain before hot isostatic pressing and the hot isostatic pressing effect.
Looking at this figure, the effect of hot isostatic pressing depends on the crystal grain size, and when the grain size exceeds 50 μm, hot isostatic pressing tends to be difficult to apply. Example 2 The material preparation process, composition, and molding were as described in Example 1. This molded body is 90%N ₂ -10%
Semiconductor porcelain was obtained by firing in H ₂ mixed gas at a temperature of 1300° C. for 2 hours. Thereafter, the semiconductor porcelain is hot isostatically pressed in Ar. The thus obtained reduced and reoxidized semiconductor porcelain was heat treated in air at a temperature of 900°C.
When the characteristics of this reduced and reoxidized semiconductor ceramic were examined in the same manner as in Example 1, characteristics very similar to those in Example 1 were obtained. In addition, in the conventional method of hot isostatic pressing dielectric porcelain fired in an oxidizing atmosphere into reducing powder, capacitor characteristics vary depending on the type and amount of reducing powder and the hot isostatic pressing temperature. This method has drawbacks such as variation and product yield of about 50 to 60%, which is 40% lower than the yield of the present invention, which is about 90%. Furthermore, looking at the relationship between the hot isostatic pressing temperature and the theoretical density ratio based on the firing temperature of the reduction-reoxidation type semiconductor porcelain capacitor shown in Fig. 4 mentioned above, the limit of hot isostatic pressing is the firing temperature T°C. It can be seen that the lower limit is 300°C lower than that. Effects of the Invention According to the present invention, the following effects are brought about. (1) High-density porcelain with a theoretical density ratio of 99% TD or higher can be obtained. (2) Semiconductorization of porcelain can be easily controlled in the atmosphere. (3) Product yield is improved. (4) Pore distribution has been improved to a maximum level of 3 μm. (5) Capacitor characteristics are improved and stabilized. As described above, the method for manufacturing a reduction and reoxidation type semiconductor ceramic capacitor of the present invention has very excellent characteristics, is extremely stable even in industrial mass production, and has great industrial value.

[Brief explanation of drawings]

Fig. 1 is a characteristic diagram showing the relationship between hot isostatic pressing (HIP) conditions and theoretical density ratio to explain an embodiment of the present invention, and Figs. 2 and 3 show an embodiment of the present invention. A diagram showing the relationship between hot isostatic pressing conditions and average grain size for explanation, and FIG. 4 is a diagram showing the relationship between hot isostatic pressing conditions and average crystal grain size. FIG. 3 is a diagram showing the relationship between hydrostatic pressure temperature and theoretical density ratio.

Claims (1)

[Claims] 1. Semiconductor porcelain is produced by firing in a reducing atmosphere T°C, and this semiconductor porcelain is heated at (T-300)°C to T°C,
After hot isostatic pressing under pressure of over 300 atmospheres,
A method for manufacturing a reduction and reoxidation type semiconductor ceramic capacitor, comprising reoxidizing the surface of the semiconductor ceramic. 2. The method for manufacturing a reduced and reoxidized semiconductor ceramic capacitor according to claim 1, wherein the average crystal grain size of the semiconductor ceramic fired at T° C. in a reducing atmosphere is 50 μm or less. 3 Firing in the air at T°C to produce dielectric porcelain, heat-treating this dielectric porcelain in a reducing atmosphere to convert it into a semiconductor, and then converting this semiconductor porcelain to (T-300)°C.
Hot isostatic pressing at ~T°C and pressure of 300 or more,
A method for manufacturing a reduction and reoxidation type semiconductor ceramic capacitor, further comprising subjecting the semiconductor ceramic surface to a reoxidation treatment. 4. The method for manufacturing a reduction and reoxidation type semiconductor ceramic capacitor according to claim 3, wherein the average crystal grain size of the dielectric ceramic fired at T° C. in the atmosphere is 50 μm or less.