KR100285239B1 - Srtio3 based grain boundary barrier layer capacitor - Google Patents

Abstract

PURPOSE: Provided is a SrTiO3 based grain boundary barrier layer capacitor(GBBLC) which shows high dielectric constant and low dielectric loss factor, as well as stable temperature property. CONSTITUTION: The capacitor is produced by adding mixture of BaO and CaO to oxide forming secondary phase. In the mixture, the molecular ratio of BaO and CaO is 0.2CaO-0.8BaO to 0.7CaO-0.3BaO. The BaO and CaO are obtained from BaO precursor and CaO precursor, respectively. The SrTiO3 based grain boundary barrier layer capacitor shows high dielectric constant and low dielectric loss factor, as well as stable temperature profile, in which dielectric constant is not substantially changed according to temperature change.

Description

SrTiO₃-based grain insulation dielectric

The present invention relates to a SrTiO ₃ based dielectric exhibiting high dielectric constant and stable temperature characteristics. More specifically described as gritty SrTiO ₃ based mouth season-insulating dielectric (Grain Boundary Barrier Layer Capacitor, below GBBLC la called) by changing the composition on the secondary of injecting in the liquid phase in the grain boundary of the SrTiO ₃ during the manufacturing process of the dielectric with an improved dielectric properties of the will be.

GBBLC is a material that forms a thin dielectric layer at the interface between semiconducting particles to make the thickness of the dielectric layer and the distance between the electrodes very small and have a high dielectric constant value. The conventional GBBLC manufacturing process is largely divided into the step of making a semiconducting sintered body and the oxide penetration step of forming a dielectric layer at the grain boundary, M. Fujimoto and WD Kingery, ″ Microstructure of SrTiO ₃ Internal Boundary Layer Capacitors During and After Processing and Resultant Electrical Properties, ″ J. Am. Ceram. Soc., 68 [4] 169-173 (1985) and Goodman, ″ Capacitors Based on Ceramic Grain Boundary Barrier Layers-a Review, ″ Advances in Ceramics, vol 1, Grain Boundary Phenomena in Electronic Ceramics, 215-231 (1981), etc. To fabricate a semiconducting sintered body, a dielectric layer is formed at the grain boundaries of semiconducting polycrystalline specimens sintered in a reducing atmosphere by adding a donor. There are several ways to form them, including R. Wernicke, ″ Formation of second-phase layers in SrTiO ₃ Boundary Layer Capacitors, ″ Advances in Ceramics, vol. 1, Grain Boundary Phenomena in El ectronic Ceramics, 261-271,1981) was made by heat-treating specimens sintered in the reducing atmosphere in the air to selectively oxidize only the grain boundaries. No. GBBLC, which is currently commercially available, is produced by a method in which oxide liquids such as PbO, Bi ₂ O ₃ , and CuO having low melting points penetrate into grain boundaries of sintered bodies to form secondary phases at grain boundaries.

The technical problem of the present invention is to prepare a SrTiO ₃ -based grain boundary dielectric dielectric composition having a high dielectric constant. In general, the higher the dielectric constant of SrTiO ₃ -based particles, the thinner the thickness of the permeated oxide liquid and the oxidized layer during liquid permeation, and the higher the dielectric constant of the permeated oxide, R. Wernicke, ″ Two-Layer Model explaining the Properties of SrTiO ₃ Boundary Layer Capacitors, '' Advances in Ceramics, vol. 1, Grain Boundary Phenomena in Electronic Ceramics, 215-231, 1981. While the present inventors are studying a method of increasing the dielectric constant of the infiltrated liquid phase, the high dielectric constant and stable property are achieved by infiltrating BaO or CaO, which is an oxide having a high dielectric constant at the grain boundary, with a mixture of the oxide permeation liquid. An SrTiO ₃ -based grain boundary dielectric dielectric (GBBLC) with temperature characteristics is invented.

1 (a) is a change in the dielectric constant value according to the measurement temperature.

(b) is the change of dielectric loss value according to the measured temperature.

Figure 2 (a) shows the dielectric constant measurement value.

(b) is the dielectric constant with temperature based on the dielectric constant value at 0 ° C.

It shows the rate of change.

Figure 3 (a) is according to the penetration time of the oxide when heat-treated at 1300 ^o C for 8 hours

It shows the change of the dielectric constant value.

(b) is the value according to the penetration time of oxide when heat-treated at 1300 ^o C for 12 hours.

It shows the change of the dielectric constant value.

The present invention consists of a first step of preparing a sintered SrTiO _3, a second step of preparing a mixed liquid forming oxide containing BaO and CaO and a third step of infiltrating the liquid forming oxide into the sintered body. The first step of manufacturing the SrTiO ₃ sintered body and the third step of infiltrating the liquid-forming oxide into the sintered body are the same as in the conventional method, but the characteristics of the present invention are the addition of BaO and CaO in the step of infiltrating the liquid-forming oxide into the sintered body. It is.

* Step 1: SrTiO ₃ sintered for several hours at SrTiO ₃ Nb ₂ O ₅ or La ₂ O after _three and mixed with a predetermined amount was added to the donor (donor) such as the shaping of this powder cold pressing than 1,400 ^o C temperature in It is prepared by sintering in a reducing atmosphere such as 95N ₂ -5H ₂ .

* Second step: The liquid-forming oxide is prepared by mixing quantitatively different molar ratios of materials that can be BaO and CaO, such as BaCO ₃ and CaCO ₃ at a high temperature in the conventional oxide liquid-forming mixture.

* Step 3: The liquid phase penetration process of the present invention is carried out in an oxidizing atmosphere, and the SrTiO ₃ intergranular dielectric dielectric has a high dielectric constant value by simultaneously injecting a substance capable of BaO and CaO into the liquid phase to be penetrated. It has the following advantages.

First, BaO added to the liquid-penetrating oxide can be expected to form a BaTiO ₃ phase having a high dielectric constant at the grain boundary through reaction with TiO ₂ excess acid present at the grain boundary.

Second, BaTiO ₃ is present at the grain boundary, which increases with increasing ferroelectric temperature at room temperature, so that the temperature characteristic of SrTiO ₃ decreases with increasing temperature from paraelectric to room temperature. As a supplementary role, the entire GBBLC can expect stable temperature characteristics with little change in dielectric constant due to temperature changes.

Third, CaO added to the liquid-penetrating oxide can mitigate the microstructure change caused by BaO. The present invention provides BaO and CaO to confirm that the dielectric constant and temperature characteristics can be greatly improved due to the reasons described above when a substance capable of mixing BaO or CaO, a mixture of BaO and CaO is added to the general penetration liquid phase. BaCO ₃ and CaCO ₃ were selected as materials and Bi ₂ O ₃ was selected as the penetration liquid phase. However, any of permeable oxides PbO, PbO-Bi ₂ O ₃ -B ₂ O ₃ and the like, which are used in the preparation of general SrTiO ₃ based GBBLC, may be added with a substance capable of BaO and CaO at a liquid permeation temperature. Accordingly, the following described and specifically described embodiments are merely exemplary and are not intended to limit the scope of the present invention.

<Example 1>

0.2 mol% Nb ₂ O ₅ donor was added to SrTiO ₃ , mixed, and sintered at 1,480 ^° C. for 5 hours. BaCO ₃ and CaCO ₃ were added to Bi ₂ O ₃ , which is a liquid-forming oxide, to prepare a mixed powder of a penetrating oxide, as shown in Table 1, in terms of an oxide composition formula. In Example 1, the temperature dependence of dielectric properties and dielectric constants was observed when a liquid-forming oxide having a change in the molar ratio of BaO and CaO based on Bi ₂ O ₃ was penetrated into the semiconductive sintered specimen in an oxidizing atmosphere.

Table 1

X CaO: BaO (mol ratio) Composition (mol ratio) 0: 0 100Bi ₂ O ₃ 0 0: 1 0.8Bi ₂ O ₃ -0.2BaO 0.2 0.2: 0.8 0.8Bi ₂ O ₃ -0.04CaO-0.16BaO 0.5 0.5: 0.5 0.8Bi ₂ O ₃ -0.1CaO-0.1BaO 0.7 0.3: 0.7 0.8Bi ₂ O ₃ -0.14CaO-0.06BaO 1.0 1: 0 0.8Bi ₂ O ₃ -0.2CaO

The mixture powder was made into a slurry and evenly applied to the surface of the finely ground sintered specimen with a uniform thickness, and then infiltrated at 1,300 ^° C. for 4 hours at a temperature above which the mixture became liquid in an oxidizing atmosphere. The liquid-penetrated specimen was finely polished on both sides so that the final thickness was 500 μm, and then silver was applied on both sides of the specimen and subjected to electrode heat treatment at 600 ^o C for 10 minutes. The specimen prepared as described above measured the temperature dependence of the dielectric constant value and the dielectric constant value while cooling the temperature with liquid nitrogen and heating again. Figure 1 (a) is a change in the dielectric constant value according to the measurement temperature, (b) is a change in the dielectric loss value according to the measurement temperature.

Referring to the dielectric properties of FIG. 1, when the molar ratio of BaO and CaO in the liquid-forming oxide is 1: 1 (X = 0.5), the highest dielectric constant and low dielectric loss are shown. On the other hand, when the oxide composition is X = 0, 1.0, low dielectric constant and high dielectric loss are shown. That is, when X = 0.5, the dielectric constant value is 2.8 × 10 ⁴ at room temperature, but when X = 0 and 1.0, the dielectric constant value is about 1.0 × 10 ⁴ at room temperature. In addition, the dielectric loss is less than 1% at room temperature when X = 0.5, which is lower than that of X = 0 and 1.0, which shows 3-5%.

FIG. 2 shows the dielectric constant values and the temperature-dependent changes of the specimens in which only Bi ₂ O ₃ was penetrated to observe the temperature dependence of the dielectric constant and that were oxidized without liquid phase, compared with the case where the oxide composition was X = 0.5. .

When BaO and CaO were infiltrated, the dielectric constant was higher than that of only Bi ₂ O ₃ . In addition, when BaO and CaO are present at the grain boundaries, the change of dielectric constant with temperature changes is small and stable. When the composition of the liquid oxide is X = 0.5, it can be seen that the change rate of the dielectric constant value with the temperature change is less than ± 10%.

<Example 2>

Figure 3 shows the change in dielectric constant value with the penetration time of the liquid-forming oxide of GBBLC prepared using the sintered body and the liquid penetrating oxide as in Example 1. Figure 3 (a) is a case of heat treatment at 1,300 ^o C 8 hours, (b) is a case of heat treatment at 1,300 ^o C 12 hours.

Even if the heat treatment time is increased, the highest dielectric constant is obtained when the composition of oxide penetrated into the liquid phase is X = 0.5. When the heat treatment time is 8 hours, the dielectric constant value is 2.2 × 10 ⁴ , and when 12 hours, the dielectric constant value is 1.8 × 10 ⁴ .

In the fabrication of SrTiO ₃ -based intergranular dielectric dielectric, when the liquid oxide added BaO and CaO developed by the present inventors is used as the grain-boundary secondary phase forming oxide, it has a high dielectric constant and stable temperature characteristics. Manufacturing is possible. The grain boundary insulating dielectric thus manufactured may be widely used in the electronic component industry.

Claims (2)

A high dielectric constant SrTiO ₃ grain boundary dielectric dielectric, characterized in that a mixture of BaO and CaO with a water ratio of 0.2CaO-O.8BaO to 0.7CaO-O.3BaO is added to the composition of the oxide forming the secondary phase. SrTiO ₃ based grain insulation dielectric. The SrTiO ₃ -based intergranular dielectric dielectric according to claim 1, which is provided from a BaO precursor and a CaO precursor.