JPH07120597B2 - Method for forming grain boundary layer of semiconductor porcelain - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for forming a grain boundary layer of a semiconductor porcelain, which comprises diffusing a metal oxide as a grain boundary insulating agent into a grain boundary of a strontium titanate-based semiconductor porcelain. is there.

[Conventional technology]

BACKGROUND ART A method for manufacturing a grain boundary layer type semiconductor ceramic capacitor or a varistor by insulating grain boundaries of a strontium titanate (SrTiO ₃ ) based semiconductor ceramic has been widely known.

As a method of insulating the grain boundaries of the SrTiO ₃ based semiconductor porcelain,
Generally, a small amount of pentavalent metal oxide such as niobium is added to SrTiO ₃ , and this is pressure-molded, and the pressure is reduced to 1400-1500 in a reducing atmosphere.
There is a method in which the grain boundaries are re-oxidized by firing at 0 ° C. and then heat treating this in the atmosphere.

However, this method has a problem that the insulation resistance and pressure resistance of the product are lowered.

As measures against this, in the past, (1) bismuth oxide (Bi ₂ O ₃ ) and manganese oxide (Mn
O ₂ ), copper oxide (CuO) and other grain boundary insulating agents are kneaded with an organic vehicle agent such as terpineol to form a paste, and this insulating paste 6 is applied to the surface of the SrTiO ₃ based semiconductor porcelain. After printing, these are arranged on a high-purity alumina plate 7 as shown in FIG. 3 (a), or on an alumina setter 8 as shown in FIG. 3 (b), and again as shown in FIG. 3 (c).
As shown in Fig. 6, a method of diffusing the metal oxide into the grain boundary layer of the semiconductor ceramic by supporting it on the alloy wire 9 and (2) coating the semiconductor ceramic such as SrTiO _{3 with a} thermoplastic binder to form a grain boundary insulating agent (3) A method of applying a grain boundary insulating agent to a semiconductor porcelain and then housing it in a semi-closed container for heat treatment (JP-A-57-87111) (JP-A-57-87111) 56-94718), (4) A semiconductor porcelain is placed in a crucible 10 closed by a plate 12 as shown in FIG. 3 (D), and a grain boundary insulating agent such as Bi ₂ O ₃ is placed in the crucible 10. There is a method in which the insulating material is vaporized and introduced, and the insulating material is vapor-phase diffused into the grain boundary layer.

[Problems to be Solved by the Invention]

By the way, in the methods (1), (2), and (3), the insulating paste 6 is applied to the surface of the semiconductor porcelain, the thermoplastic binder is applied, and the grain boundary insulating agent is attached. It is inevitable that the coating amount becomes complicated and the amount of diffusion varies, and the amount of diffusion of the diffusion species also varies, resulting in non-uniform characteristics and large standard deviation. It had the drawback of poor mass productivity.

In the method (4), when the insulator is vapor-phase-diffused in the semiconductor porcelain grain boundaries, it is housed in the high-purity alumina crucible 10 and closed by the high-purity alumina plate 12, and is heated in a semi-sealed state. However, there is a problem in the uniformity of the flow of the vaporized insulating material in the filling layer, and it is unavoidable that the characteristics vary, and the standard deviation becomes large.

The present invention has been made in view of the above circumstances, and provides a method for forming a grain boundary layer of a semiconductor porcelain which has uniform electrical characteristics, a small standard deviation, a simple manufacturing process, and excellent mass productivity. With the goal.

[Means for Solving the Problems]

The method for forming a grain boundary layer of a semiconductor porcelain of the present invention is a method for forming a grain boundary layer of a semiconductor porcelain in which a metal oxide is diffused in a grain boundary of a strontium titanate-based semiconductor porcelain. The pressure-molded metal oxide is mixed in a container and heat-treated to diffuse the metal oxide into a grain boundary of the semiconductor ceramic.

[Action]

When strontium titanate-based semiconductor porcelain and metal oxide as a grain boundary insulating agent pressure-molded into pellets are mixed in a container and heat-treated, the metal oxide is uniformly diffused in the grain boundaries of each semiconductor porcelain. The variation in the electrical characteristics of the obtained grain boundary layer type semiconductor porcelain product is small.

Here, as the grain boundary insulating agent, bismuth oxide (Bi
₂ O ₃ ), manganese oxide (MnO ₂ ), copper oxide (CuO),
Oxides of sodium, cesium, cobalt and rubidium are also suitable. Further, oxides of the above elements include compounds having a property of vaporizing during heating for diffusion, such as carbonates.

Further, the pellet-shaped metal oxide may be composed of one or more kinds of the metal oxides of the above-mentioned elements, that is, only the oxide of the element acting as a grain boundary insulating agent, but more preferably, It is better to include refractory oxides as bone agents.

The aggregate has the function of maintaining the shape of the pellet in the process of vaporization of the grain boundary insulating agent during the diffusion treatment of the grain boundary insulating agent and keeping voids in the filling layer of the semiconductor porcelain. The voids are extremely effective for promptly and uniformly diffusing in the filled layer of the vaporized grain boundary insulating agent semiconductor porcelain.

Example 1 Hereinafter, an example in which the method of the present invention is applied to manufacture of a capacitor will be described in detail with reference to the drawings.

FIG. 1 is a schematic perspective view showing a container used for carrying out the method of the present invention, and FIG. 2 is a schematic sectional view showing an implementation state of the method of the present invention. In FIGS. 1 and 2, reference numeral 5 is a container in which a crucible 4 made of high-purity alumina is sealed by a lid 3 made of a high-purity alumina plate, and the semiconductor porcelain 1 and 15% by weight are contained in the container 5. To some extent, the metal oxide pellets 2 as the grain boundary insulating agent are mixed.

The semiconductor porcelain 1 contains, for example, SrTiO ₃ containing 0.1 to ₂ mol% of Nb ₂ O ₅ and M
After adding 0.1 to ₂ mol% of nO ₂ and mixing and drying,
For example, a binder such as polyvinyl alcohol is added and granulated, and this is pressure-molded into a disk shape with a diameter of 10 mm and a thickness of 0.8 mm to obtain an element body, and then this element body is subjected to a reducing atmosphere (flow ratio: H ₂ =
1 to 15%, N ₂ = 99 to 85%) at 1400 to 1550 ° C 4.0 to 1
It was formed by baking for 0.0 hours.

The metal oxide pellet 2 includes a refractory oxide as an aggregate, for example, an aggregate made of alumina, and a metal oxide as a grain boundary insulating agent, for example, Bi ₂ O ₃ plain or Bi ₂ O ₃ / CuO. Ingredient system (molar ratio 9/1) or Bi ₂ O ₃ / CuO / Na ₂ O ternary system (molar ratio 4.5 / 1
/4.5) with a weight ratio of 9/1 and a diameter of 5 mm and a thickness of 0.5
It is pressed into a mm disk shape.

As the grain boundary insulating agent, it is needless to say that it is a substance having an insulating effect, but a substance having at least a vaporization temperature lower than the melting point of the semiconductor porcelain and the aggregate of the pellet is desirable.

Here, the aggregate is the main material constituting the pellet,
It means that it has the function of holding the shape of the pellet,
For example, Al ₂ O ₃ , SiO ₂ , MgO, AlN, Si ₃ N ₄ etc. carbides, nitrides,
Alternatively, materials that are chemically stable at high temperatures such as compounds and mixtures thereof are used.

The semiconductor porcelain 1 and the metal oxide pellets 2 as described above are mixed in the container 5 in the atmosphere at 1100 ° C. (1050 to 13
After the metal oxide is diffused in the grain boundaries of the semiconductor ceramic 1 by firing at 00 ° C) for 2 hours, the semiconductor ceramic 1 is taken out, and an electrode material such as silver paste is baked on both sides to form an electrode. Get the capacitor.

Table 1 below shows the electrical characteristics of the semiconductor ceramic capacitor obtained by the method of the present invention and its standard deviation (σ).
In the sample lot number, a is Bi ₂ O ₃ alone as an insulating agent, b is a binary system of Bi ₂ O ₃ / CuO (molar ratio 9/1), and c is Bi.
_It uses a ternary system of ₂ O ₃ / CuO / Na ₂ O (molar ratio 4.5 / 1 / 4.5). Also, the capacitance C (nF) and dielectric loss tangent in the table
The tan δ (%) is a value measured at 1 kHz AC and 1 V voltage, and the insulation resistance IR (Ω) is a value obtained by a 25-minute DC 25 V value. Each characteristic value in the table is the average value of 30 samples.

As a conventional example, the above three types of insulating agents are pasted on the surface of a sintered body obtained by firing in a reducing atmosphere and screen-printed, and as shown in FIG. It was made by firing in a medium at 1100 ° C. for 2 hours. Table 2 shows the results of the conventional example.

As is clear from Tables 1 and 2, the electrical characteristics of the inventive example are better than those of the conventional example, and the standard deviation thereof is 1/5 to 1/3 in capacitance C and dielectric loss tangent. The tan δ is 1/5 and the insulation resistance is 1/3 to 1/2, which is extremely small, and capacitors with good electrical characteristics are obtained without variation.

[Example 2] As in Example 1, the semiconductor porcelain and the metal oxide pellets as the grain boundary insulating agent, which are separately formed in advance, are mixed in the container 5 and housed in a semi-sealed state. Then, in this state, it is baked in the atmosphere at 1100 ° C. for 2 hours. By this, the sintered body on which the grain boundary insulating layer is formed is taken out, and silver paste or the like is baked on both surfaces thereof to form electrodes, thereby obtaining a capacitor.

Semiconductor porcelain is SrTiO ₃ with 0.1-2 mol% of Nb ₂ O ₅ and 0.1-2 mol.
l% MnO ₂ is added, mixed and dried, then polyvinyl alcohol, for example, is added as a binder and granulated, and this is pressure molded into a disk shape with a diameter of 10 mm and a thickness of 1.0 mm the resulting, then the body reducing atmosphere _{(H 2: 1~15%, N} 2: 99~85
%) In calcination at 1450 ° C. for 6 hours.

Further, the metal oxide pellets include Al ₂ O ₃ as an aggregate, and Bi ₂ O ₃ alone or a mixture of Bi ₂ O ₃ and Co ₂ O ₃ (molar ratio 9/1), or Bi ₂ O 3. A mixture of ₃ and Co ₂ O ₃ and Rb ₂ O ₃ (molar ratio: 4.5 / 1 / 4.5) was added and mixed in a weight ratio of 9/1 with the aggregate and mixed to give a circle with a diameter of 15 mm and a thickness of 0.5 mm. It was pressed into plates.

The comparison test results of the example of the present invention formed as described above and the separately prepared conventional example are shown.

In the conventional example, each of the above,
Screen-print each paste-like grain boundary insulating agent of
Heat treatment was performed in the mode shown in FIG. 3 (a) (calcination in air at 1100 ° C. for 2 hours) to prepare three types of samples.

The electrical characteristics, particularly the dielectric characteristics and the varistor characteristics, of the present invention example and the conventional example were measured. The results are shown in Tables 3 and 4. Table 3 shows the results for the examples of the present invention, and Table 4 shows the results for the conventional examples.

Note that in the sample lot numbers in Tables 3 and 4, 1 is Bi ₂ O ₃ alone as an insulating agent, 2 is Bi ₂ O ₃ / Co ₂ O ₃ , and 3 is Bi ₂ O ₃ / Co ₂ O.
₃ / Rb ₂ O ₃ is used.

The current / voltage characteristics of the varistor are defined by the following equation.

I = [V / C] ^α However, I: current flowing in the varistor V: voltage applied to both ends of the varistor C: varistor intrinsic constant α: non-linear coefficient The evaluation of the varistor is indicated by the magnitude of the non-linear coefficient α,
The larger α is, the greater the varistor effect is.

Furthermore, the varistor voltage is represented by the terminal voltage V ₁ mA when a current of 1 mA is applied to the sample.

The nonlinear coefficient α is calculated by the following formula.

However, V ₁₀ mA: Terminal voltage when a current of 10 mA is applied to the sample As is apparent from Tables 3 and 4, the present invention examples are standard deviations of dielectric characteristics such as capacitance and dielectric loss, and electrical characteristics such as varistor characteristics of varistor voltage V ₁ mA and nonlinear coefficient α. σ is significantly smaller than the conventional example in Table 4, for example, the capacitance is about 1/5 to 1/2 and the dielectric loss is 1/10.
It can be seen that the varistor voltage V ₁ mA can be reduced to about 1/2 to 3/4, and the nonlinear coefficient α can be reduced to about 1/3 to 5/6 to about 1/5.

Thus, in the semiconductor porcelain obtained by such a method of the present invention, both the dielectric characteristics and the varistor characteristics can be uniformly positive, and a single element can have both functions of a capacitor and a varistor. It will be possible.

Also, the amount of the grain boundary insulating agent in the method of heat treatment by mixing the semiconductor porcelain and the pellet-shaped grain boundary insulating agent in the semi-closed container,
The amount of diffusion can be controlled. Therefore, the work of applying the grain boundary insulating agent, which is required in the conventional method, is unnecessary, and the variation in the characteristics, which is a problem when the vapor phase diffusion method is used, is small. Thus, the mass productivity of semiconductor porcelain is improved, and it becomes possible to easily cope with lot variations.

Although the semiconductor ceramic capacitor and the varistor have been described in the first and second embodiments as described above, it is needless to say that the method of the present invention can be similarly applied to the thermistor and the like.

〔The invention's effect〕

As described above in detail, according to the method for forming a semiconductor ceramic grain boundary layer of the present invention, since it is not necessary to apply or add an insulating agent to each semiconductor ceramic, the manufacturing process is simple and suitable for mass production. Further, application and adjustment of addition amount are easy.

Furthermore, it can have good results in electrical characteristics such as capacitance, dielectric loss tangent, insulation resistivity, varistor characteristics, etc. of the product, and its standard deviation is extremely small compared with the result of the conventional method, resulting in product variation. Excellent effects such as less

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing a container used for carrying out the present invention, and FIG. 2 is a schematic vertical sectional view showing a working state of the present invention.
FIGS. 3A to 3D are schematic views for explaining a conventional method for forming a semiconductor ceramic grain boundary layer. 1 ... Semiconductor porcelain, 2 ... Metal oxide pellets 3 ... High-purity alumina lid, 4 ... High-purity alumina crucible, 5 ... Container

Claims (2)

[Claims] 1. A method for forming a grain boundary layer of a semiconductor porcelain, which comprises diffusing a metal oxide in a grain boundary of a strontium titanate-based semiconductor porcelain, comprising: a strontium titanate-based semiconductor porcelain and a grain boundary insulating agent pressure-molded in a pellet form. A method for forming a grain boundary layer of a semiconductor porcelain, which comprises mixing a metal oxide in a container and heat-treating the mixture to diffuse the metal oxide into a grain boundary of the semiconductor porcelain. 2. The method for forming a grain boundary layer of a semiconductor porcelain according to claim 1, wherein the metal oxide contains a refractory oxide as an aggregate.