JPH0460329B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for manufacturing a semiconductor ceramic capacitor that can simultaneously produce high-density ceramics with a theoretical density ratio of 99% TD or higher and ceramics with high grain boundary strength. Structure of conventional example and its problems A grain boundary dielectric layer type semiconductor capacitor has a grain boundary region between semiconductor crystals with high resistance, and a dielectric layer is provided at the grain boundary. This grain boundary layer type utilizes the area of 10 ^-2 to several μm near the grain boundaries, and the capacitor characteristics are influenced by the state of the grain boundaries.
In the conventional method, the bonding strength of the grain boundaries is weak, and when a dielectric layer is provided at the grain boundaries, the thickness of the dielectric layer varies, the strength of the dielectric layer is weak, and the withstand voltage characteristics and dielectric loss are poor. It was hot. There is also a method of hot isostatically pressing dielectric porcelain fired in an oxidizing atmosphere in reducing powder to obtain semiconductor porcelain and dense ceramics at the same time, but it is difficult to control the atmosphere for semiconductor production. It is difficult, and the quality stability and product yield are poor. In addition, hot isostatic pressing is sometimes performed after providing a dielectric layer at the grain boundaries of semiconductor porcelain, but in this method, the temperature under hot isostatic pressing conditions must always be below the diffusion treatment temperature. If the diffusion temperature is lower than (sintering temperature - 300°C), there is a drawback that the hot isostatic pressing effect is not produced. Purpose of the invention The present invention eliminates the conventional drawbacks and achieves a theoretical density ratio of 99%.
It is an object of the present invention to provide a method for manufacturing a semiconductor ceramic capacitor that can simultaneously obtain high-density ceramics of TD or higher and ceramics with high grain boundary strength, and that provides high withstand voltage characteristics, low dielectric loss, and excellent mechanical properties. This is the purpose. Structure of the Invention In order to achieve the above object, the present invention hot isostatically presses porcelain made into a semiconductor by firing in a reducing atmosphere, and then thermally diffuses a diffusing agent into the grain boundaries of the semiconductor porcelain to create a dielectric material. By forming a dielectric layer, we were able to obtain a grain boundary dielectric layer type semiconductor ceramic capacitor that provides high withstand voltage characteristics, low dielectric loss, and excellent mechanical properties. DESCRIPTION OF EMBODIMENTS The present invention will be described below along with one embodiment. In the sample preparation process, commercially available industrial raw materials SrCO ₃ powder (purity 99.9% or higher), TiO ₂ powder (purity 99.9% or higher), and commercially available reagent grade Nb ₂ O ₅ powder were used as the semiconductor magnetic composition. The compositions were blended to have the composition ratios shown in Table 1, wet mixed using a urethane-lined pot to prevent contamination with impurities, dried, and then pre-fired at a temperature of 1200°C. Table 1 Semiconductor porcelain composition (mol%) SrCO ₃ TiO ₂ Nb ₂ O ₅ 50.10 49.85 0.05 After wet-pulverizing this pre-fired material and drying it, a polyvinyl alcohol aqueous solution was used as a binder and mixed.
The grain size was adjusted to 32 meters. This sized powder has a diameter of 13
mm and 0.5 mm thick under a pressure of 1 t/cm ² , and after heat-treating these molded bodies in air at 1000°C, a mixed gas stream of 90% N ₂ -10% H ₂ was applied. Semiconductor porcelain was obtained by firing for 3 hours at a temperature of 1400°C. Thereafter, the semiconductor porcelain is hot isostatically pressed in Ar gas. The relationship between the pressing conditions at this time, the theoretical density ratio of the porcelain, and the average grain size is shown in Figures 1 and 2.
As shown in the figure. Next, as a diffusing agent, the composition is Bi ₂ O ₃ −Cu ₂
An O-based paste was used and evenly applied to the surface of the semiconductor ceramic element. The semiconductor ceramic element coated with the diffusing agent as described above was subjected to a diffusion treatment at a temperature of 1100° C. in the atmosphere. Ag electrodes were baked on both sides of the disk-shaped element of the grain boundary dielectric layer type semiconductor porcelain obtained in this way to form a capacitor element, and the dielectric constant ε _a (measurement frequency 1 KHz)
Dielectric loss tanδ (1KHz), boost breakdown voltage V _b (V/
mm) and Bitkers hardness _Hv (Kg/mm ² , 500g, 15 seconds load) were measured. The results are shown in Table 2. Here, comparative sample No. 11 is a conventional grain boundary dielectric layer type ceramic capacitor that is not subjected to the hot isostatic pressing process. 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. According to the present invention, samples No. 1 to No. 7 are compared to comparative sample No.
11, about 60% for ε _a , about 40% for Vb, Hv
Excellent capacitor characteristics can be obtained with approximately 30% increase in tan δ and approximately 60% decrease in tan δ. No.8～No.10
The sample 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 1100℃, and the temperature effect decreases below 300 atm, both of which result in high density (over 99% TD). I can't get it.
Therefore, in the conventional example of hot isostatic pressing after diffusion treatment, the hot isostatic pressing effect cannot be obtained if the diffusion treatment temperature is less than 1100°C. In addition, as shown in Figure 2, the average grain size of semiconductor porcelain depends on the hot isostatic pressing temperature, but does not depend much on the hot isostatic pressing pressure, and the hot isostatic pressing temperature is the firing temperature ( When the temperature exceeds 1400°C (in the figure), grain growth occurs rapidly, and as can be seen from the results in No. 10 in Table 2, the capacitor characteristics deteriorate. In other words, when the firing temperature is T°C, no increase in porcelain density is observed when the hot isostatic pressing temperature is below (T-300)°C, and when it exceeds T°C, grain growth is promoted and foreign phase precipitation occurs. This causes deterioration of capacitor characteristics. In addition, the hot isostatic press pressure
No increase in porcelain density is observed below 300 atm. 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. There are disadvantages such as variation and product yield of about 30 to 40%, which is 40 to 60% lower than the yield of the product of the present invention, which is about 70%. Effects of the Invention According to the present invention, the following effects are brought about. (1) High-density ceramics with a theoretical density ratio of 99% TD or higher can be obtained. (2) Capacitor characteristics are improved and stabilized. (3) Product yield is improved. (4) Pores precipitated at grain boundaries are eliminated, and grain boundary strength can be strengthened. As described above, the method for manufacturing semiconductor ceramic capacitors of the present invention has extremely excellent performance and is extremely stable even in industrial mass production.
It has great industrial value.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the relationship between hot isostatic pressing (HIP) conditions and theoretical density ratio to explain an embodiment of the present invention, and Figures 2 and 3 are diagrams to explain an embodiment of the present invention. FIG. 3 is a diagram showing the relationship between hot isostatic pressing conditions and average crystal grain size for achieving the desired results.

Claims (1)

[Claims] 1. Semiconductor porcelain is produced by shaping the raw material into any desired shape and firing it at T°C in a reducing atmosphere, and then heating the semiconductor porcelain at (T-300)°C to T°C at a temperature of 300 atmospheres or more. A method for manufacturing a semiconductor ceramic capacitor, which comprises hot isostatic pressing under atmospheric pressure and then thermally diffusing a diffusing agent into the grain boundaries of the semiconductor ceramic. 2. The method for manufacturing a 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.