JPH06151233A - Manufacture of semiconductor porcelain composition - Google Patents

Abstract

PURPOSE:To enhance productivity by suppressing the deposition between molded bodies when a reducing atmosphere firing operation is conducted, and to improve the electric characteristics such as insulating property, capacitive and the like as a capacitor by a method wherein the dew point of reducing atmosphere gas in a semiconductivity- giving firing process is set at 0 to 35 deg.C. CONSTITUTION:In the manufacturing method for a semiconductor porcelain composition containing a semiconductivity-giving firing process, in which the mixture of strotium titanate compound or titanium oxide and the carbonate of strontium and the raw material mixture containing silicon dioxide are brought into a state of semiconductivity, and a grain boundary insulating process in which a crystal grain boundary layer is brought into an insulated state after performance of the semiconductivity-giving firing process, the dew point of the reducing atmosphere of the semicoductivity-giving firing process is set at 0 to 35 deg.C. This setting of dew point is conducted by introducing the reducing gas such as H2, N2, Ar and the like into a vapor atmosphere chamber of 0 to 35 deg.C. The vapor contained in the reducing gas in decomposed into hydrogen and oxygen when the temperature of the atmosphere is raised in the firing process, the reductive firing becomes weaker by the boosting of the partial pressure of oxygen, and the welding between the molded bodies can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a semiconductor porcelain composition in which an insulating layer is formed on a crystal grain boundary of the semiconductor porcelain, and more specifically, it is mounted on communication equipment, audio equipment, and various OA equipment. The present invention relates to a method for producing a semiconductor porcelain composition used as a capacitor or a varistor in an electronic circuit or the like.

[0002]

2. Description of the Related Art A grain boundary insulation type semiconductor porcelain composition is one in which an insulating layer is formed by thermally diffusing a metal oxide or the like at crystal grain boundaries of a semiconductor made into a ceramic, and is mainly used as a capacitor. There is. In general, this type of capacitor utilizes a thin grain boundary (insulating layer) thickness of several nm, so that a small size and a large capacitance can be obtained.

As the main raw materials of the semiconductor porcelain composition currently used, there are two kinds of material systems, barium titanate type and strontium titanate type. The barium titanate system has a large apparent relative permittivity ε _app corresponding to the physical properties of barium titanate, but there is a problem that its value is easily affected by temperature and frequency. On the other hand, the apparent relative permittivity ε _app of the strontium titanate type is smaller than that of the barium titanate type, but its value is not easily affected by temperature and frequency, the dielectric loss is small, and it is easy to design the grain boundary. There is. The apparent relative permittivity ε _app is defined by the following formula 1 and represents one element characteristic of the semiconductor ceramic.

[0004]

Where ε _app = C · S / d, where C is the capacitance, S is the electrode area, and d is the inter-electrode distance.

In recent years, in particular, electronic devices and electronic circuits are often used in a high frequency region, and are often used in a severe environment such as automobile parts, and have excellent reliability in high frequency characteristics and temperature characteristics. Capacitors with high properties are required, and strontium titanate-based capacitors are drawing attention.

At present, Bi, Mn, Cu, Pb, are present in the crystal grain boundaries of semiconductor porcelain mainly containing strontium titanate.
A metal oxide such as Al was added and thermally diffused to obtain a high relative permittivity, calcium titanate was solid-dissolved with strontium titanate, and an alkali metal was thermally diffused to grain boundaries to give a varistor function. In addition to conventional low frequency analog circuits, which have been mainly used in the past, their applications are expanding to noise filters for power supplies, noise absorbing elements for semiconductor devices, and the like.

In order to develop sufficient capacitance in the grain boundary insulation type semiconductor porcelain, it is necessary to accelerate the growth of the porcelain crystal to a diameter of several tens of μm, and reducing atmosphere firing is performed as a means thereof. When firing in a reducing atmosphere, the molded body is placed in, for example, an alumina crucible or a zirconia crucible and fired. However, in order to improve the productivity, a plurality of molded bodies are stacked and fired at the same time in most cases.

However, when high-temperature firing at 1400 ° C. or higher is performed in a reducing atmosphere, liquid phase sintering proceeds, so that wetting occurs between the compacts during firing, causing inter-sintering of the compacts. In many cases, it causes welding of the molded body. When welding between the molded bodies occurs, it becomes difficult to separate the sintered body elements, so that a decrease in productivity is unavoidable, and it has been a cause of raising the product cost. Japanese Patent Application Laid-Open No. 54-2 is disclosed as a disclosed example in which the welding between the molded bodies is relaxed and the productivity is improved.
7948 (Pr added as a semiconducting agent) and JP-A 54-44750 (P added as an auxiliary component).

[0009]

However, the above-mentioned Japanese Patent Laid-Open No. 54-27948 (P as a semiconducting agent is used).
(with r added) and those described in JP-A-54-44750 (where P is added to the auxiliary component), the suppression of welding is insufficient and the insulation resistance is not sufficiently high. was there.

The present invention has been invented in view of the above-mentioned problems, and it is possible to improve productivity by suppressing welding between compacts during firing in a reducing atmosphere for semiconductor formation, and as a capacitor. It is an object of the present invention to provide a method for producing a semiconductor porcelain composition having electrical characteristics such as insulation and capacitance which are suitable for mounting an electric circuit.

[0011]

In order to achieve the above object, a method for producing a semiconductor porcelain composition according to the present invention comprises a strontium titanate compound or a mixture of titanium oxide and strontium carbonate and silicon dioxide. In a method for producing a semiconductor porcelain composition, which comprises a semiconducting firing step of semiconducting a raw material mixture, and a grain boundary insulating step of insulating the grain boundary layer after the semiconducting firing step.
It is characterized in that the dew point of the reducing atmosphere gas is set to 0 to 35 ° C. in the semiconductor conversion firing step.

[0012]

According to the above method, the dew point of the reducing atmosphere in the semiconductor-forming firing step is set to 0 to 35 ° C. When the dew point is not set at all (when reducing gas is passed as it is)
Is too reducible (Po ₂ is about 10
^-25 atm), which causes problems in composition control of SrTiO ₃ system. The dew point is set by passing a reducing gas such as H ₂ , N ₂ and Ar through a steam atmosphere chamber at 0 to 35 ° C., and the reducing gas contains a predetermined amount of steam. When the temperature of the atmosphere becomes high in the firing step, the water vapor contained in the reducing gas is decomposed into hydrogen and oxygen, and the partial pressure of oxygen increases, so that the reducing atmosphere is weakened. Therefore, reduction firing is subtly weakened and liquid phase sintering is suppressed,
It is considered that welding between the molded bodies is prevented. Experiments have also revealed that the reduction firing effect is weakened, whereby the growth of ceramic crystal grains is suppressed to an appropriate size up to a diameter of several tens of μm, and the electrical characteristics are improved.

That is, by setting the dew point as described above, the welding ratio between the compacts in the sintered compact is suppressed to 3% or less, and the average crystal grain size D _G is 25 to 35 μm.
It becomes possible to control within the range of m. The apparent relative permittivity ε _app , which is a measure of capacitance as an electrical characteristic, is maintained at 3.0 × 10 ⁴ or more, and the dielectric loss DF (%) is suppressed at 0.6% or less. It was confirmed that the insulation resistance IR (Ω) was 2.0 × 10 ¹⁰ Ω or more in the case of the DC 25 V rating, and the insulating property as the capacitor was sufficiently satisfied.

[0014]

EXAMPLES Examples of the method for producing a semiconductor porcelain composition according to the present invention will be described below. First, SrCO ₃ , TiO ₂ , Nb ₂ O ₅ ,
An appropriate amount of boulders, a dispersant, and pure water are added to the main raw material made of SiO ₂ and mixed in a pot mill for 24 hours. The mixed slurry-like raw materials are dehydrated and dried and crushed. This crushed powder is transferred into a firing crucible made of, for example, zirconia, and 115
It is calcined and synthesized at 0 ° C. to obtain a ceramic, and it is confirmed by X-ray analysis, composition analysis, etc. that a predetermined solid solution ceramic is synthesized.

Next, the calcined synthetic ceramic is crushed to 1.0
The particles are sized using a uniform powder sieve of about μm. An organic binder or the like is added to this powder to give a diameter of 10 mm and a thickness of 50.
It is molded into a disk shape of 0 μm. This molded body is 1000 ° C
Keep it warm with and remove the organic binder. After that, a compact is placed in an alumina firing crucible and firing is performed in a reducing atmosphere to simultaneously sinter the ceramic and convert it into a semiconductor. This reducing atmosphere firing is performed with 1 to 15% hydrogen and 8 nitrogen.
Using a reducing gas in which a mixed gas of 5 to 99% is passed through a water vapor atmosphere chamber having a set dew point of 0.0 to 35.0 ° C., in the reducing gas atmosphere, a temperature range of 1380 to 1450 ° C. It is performed by firing for 0.0 to 8.0 hours.

Next, the obtained sintered body is thoroughly washed with an organic solvent (eg acetone) and hot water, and then a composition containing Bi and Cu components at the same time is kneaded to insulate the ceramic grain boundaries. The paste is applied to the surface of the sintered body. The coating amount is about 20 to 50 mg per 1 g of the sintered body. This is subjected to grain boundary insulation firing in the temperature range of 1000 to 1350 ° C. for 0.5 to 4.0 hours to complete the production of the semiconductor porcelain composition. It was confirmed by EPMA that the Bi and Cu components were diffused.

Commercially available Ag paste for electrodes was printed on both surfaces of the semiconductor porcelain composition, and the electrodes were baked at 800 ° C. to prepare samples for evaluation. The main raw materials were SrCO ₃ , TiO ₂ , and Nb.
₂ O ₅ and SiO ₂ were used, but SrTiO ₃ , Nb ₂ O ₅ and SiO ₂ were used as main raw materials.
Although Ag paste may be used for the electrode, any other material may be used as long as it has a function of an electrode.

Evaluation of the completed semiconductor porcelain composition was performed as follows. The state of welding between the formed bodies was confirmed for all the formed bodies after firing in the reducing atmosphere at each set dew point, and the welding rate between the formed bodies for each set dew point was calculated. The ceramic crystal grain size of the sample was measured by SEM observation of the sample cross section. The data of the average crystal grain size D _{G in} Table 1 is a value calculated by performing SEM observation on 30 randomly selected grains in each composition.

The electrical characteristics are apparent relative permittivity ε _app ,
The dielectric loss DF (%) and the insulation resistance IR (Ω) were evaluated. The apparent relative permittivity ε _app is a value converted from the size of the molded body based on the electrostatic capacitance measured at AC 1 kHz, 1 V and room temperature using an impedance analyzer. The dielectric loss DF (%) is also a value measured at AC 1 kHz, 1 V and room temperature. Further, the insulation resistance IR (Ω) was calculated by applying a direct current of 25 V between the electrodes as a rated voltage and calculating the current value one minute after the application. The electrical property data in Table 1 is SrTiNb _0.004 O ₃ -Si
Randomly 10 semiconductor porcelain compositions for a composition of _0.002
0 is taken out and the average value of them is shown.

[0020]

[Table 1]

As is apparent from Table 1, the test condition No. using the set dew point within the range of claim 1 is as follows. In Nos. 4 to 11, the welding rate between the compacts of the sintered body could be suppressed to 3% or less. The average crystal grain size D _G is 25 to 35 μm.
Could be controlled within the range of. As electrical characteristics,
2. The apparent relative permittivity (ε _app ) which is a measure of capacitance is determined.
It can be maintained at 0 × 10 ⁴ or more, the dielectric loss (DF;%) can be suppressed to 0.6% or less, and the insulation resistance IR (Ω)
Is 25 × 10 ¹⁰ Ω or more in the case of a DC 25V rating, which proves that the insulating property as a capacitor is sufficiently satisfied. As described above, the porcelain compositions according to the examples have excellent electrical characteristics, and it is possible to manufacture a large-capacity capacitor having high insulation performance.

However, the test condition No. 1-3, 12-1
No. 4 is the one that was fired at the set dew point outside the scope of claims (marked with (*) in Table 1), the welding ratio between the molded bodies of the sintered body was high, and the apparent relative dielectric constant ε _app It can be seen that the dielectric loss DF (%) is deteriorated and a value satisfying the electrical characteristics is not obtained.

As described above, according to the method according to the embodiment, it is possible to suppress the welding between the compacts during firing in a reducing atmosphere for semiconductor formation, and therefore, it is possible to enhance the productivity and to further improve the capacitor. As a result, it is possible to obtain a semiconductor porcelain composition having electrical characteristics such as insulation and capacitance suitable for mounting an electric circuit.

[0024]

As described above in detail, in the method for producing a semiconductor porcelain composition according to the present invention, a strontium titanate compound or a mixture of titanium oxide and strontium carbonate and a raw material mixture containing silicon dioxide are converted into semiconductors. In the method for producing a semiconductor porcelain composition, the method comprises: a semiconductorizing firing step of: and a grain boundary insulating step of insulating a crystal grain boundary layer after the semiconductorizing firing step. Since the dew point of is set to 0 to 35 ° C., it is possible to suppress the welding between the molded bodies in the semiconductorizing and firing process, and thus to improve the productivity, and further, to improve the insulation and capacitance of the capacitor. A semiconductor porcelain composition having electrical characteristics suitable for mounting an electric circuit can be obtained.

[0025]

Claims (1)

[Claims] 1. A semiconducting firing step of semiconducting a raw material mixture containing a strontium titanate compound or a mixture of titanium oxide and strontium carbonate and a silicon dioxide, and a crystal grain boundary layer is formed after the semiconducting firing step. In the method for producing a semiconductor ceramic composition including a grain boundary insulating step of performing grain boundary insulation, the dew point of the reducing atmosphere gas in the semiconductor conversion firing step is set to 0 to 35 ° C. Manufacturing method.