JPH06271354A - Intergranular insulation type semiconductor porcelain composition - Google Patents

Abstract

PURPOSE:To obtain the subject composition which prevents the abnormal growth of particles at the time of firing and maintains a prescribed breakdown voltage and apparent dielectric constant by incorporating a specific amount of the glass component having average grain size of crystal particles and max. grain size less than respective values and having the crystal particles of specified composition. CONSTITUTION:In the SrTiO3 series intergranular insulation type semiconductor porcelain composition having <=10mum average grain size of crystal particles and <=20mum max. grain size, the composition is incorporated with the crystal particles consisting of (Sr1-x-y-zCaxMgyMz)Ti2O3, wherein the non-stoichiometrical values of x, y, z and alphais x<=0.50, y<=0.20, 0.002<=z<=0.02, and 0.990<=alpha<=1.02, M is the additive being converted into semiconductor by the valency controlling of Y, La, Ce, Cd, Dy, Ho, Er, etc., and incorporated with <=1000ppm glass component in wt. ratio based on the starting material of the crystal particles. The intergranular insulation type semiconductor porcelain composition which prevents the abnormal growth of particles generating at the time of firing and maintains a prescribed breakdown voltage and apparent dielectric constant is provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a SrTiO ₃ type grain boundary insulating semiconductor ceramic composition used as a capacitor.

[0002]

2. Description of the Related Art Conventionally, SrTiO ₃ based grain boundary insulation type semiconductor ceramic capacitors have characteristics of having a higher apparent dielectric constant, excellent temperature characteristics, and smaller dielectric loss than BaTiO ₃ ceramic capacitors. Known as.
The applicant of the present application has proposed, as an improvement of this type of SrTiO ₃ -based grain boundary insulating type semiconductor ceramic capacitor, a composition in which crystal grains have an average grain size of 10 μm or less and a maximum grain size of 20 μm or less (JP-A-64- 63204 publication). This type of composition contains a glass component such as SiO ₂ in a number of 1 as a sintering aid (mineralizing agent) and as a contamination from crushed cobblestones used in the mixing and crushing process when preparing raw materials.
Contains about 000 ppm. However, the glass component is easily separated from the main raw material in the drying step after mixing and pulverizing the raw materials, it is difficult to uniformly disperse a minute amount of the glass component in the raw material, and the glass components are nonuniformly present.

The glass component which exists non-uniformly in this way locally forms a liquid phase during firing, and the driving force for firing becomes imbalanced, so that crystal grains (abnormal particles) of 20 μm or more occur. It will be easier. Further, a large deviation of the glass component is observed as a poor appearance with growth of abnormal particles around the white spot. When such abnormal grain growth occurs, the number of crystal grain boundaries in the electric field direction at that portion decreases, and the total thickness of the insulating layer becomes thin, so that the breakdown voltage decreases. In particular, since the white spots have a ring-shaped region around them that has grown as abnormal particles, the breakdown voltage is reduced to 1/3 to 1/10.

The growth of abnormal particles can be suppressed by lowering the firing temperature from the optimum firing temperature by about 20 to 30 ° C. However, when the firing temperature is lowered, the apparent dielectric constant ε is lowered. For example, the firing temperature is 2
It has been confirmed that when the temperature is lowered by 0 ° C., the apparent dielectric constant ε is reduced by about 15%.

[0005]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a grain boundary insulating semiconductor ceramic composition capable of preventing the growth of abnormal particles generated during firing and maintaining a predetermined breakdown voltage and apparent dielectric constant. To provide. In order to achieve the above object, the grain boundary insulating semiconductor ceramic composition according to the present invention has an average grain size of 10 μm or less and a maximum grain size of 2 or less.
Consisting of SrTiO ₃ -based crystal particles having a size of 0 μm or less,
It contains a glass component in an amount of about 1000 ppm or less in weight ratio with the crystal grain raw material. The crystal particles are (Sr _1-XYZ Ca _X M
g _Y M _Z ) TiαO _{3 and} the nonstoichiometric values of X, Y, Z and α are X ≦ 0.50, Y ≦ 0.20,
0.002 ≦ Z ≦ 0.02, 0.990 ≦ α ≦ 1.02
And M is Y, La, Ce, Gd, Dy, Ho, Er
It is an additive that is converted into a semiconductor by controlling the valence of the above.

The SrTiO ₃ based porcelain composition having an average grain size of crystal grains of 10 μm or less and a maximum grain size of 20 μm or less does not oxidize to the inside of the crystal grains, and exhibits good breakdown voltage and dielectric constant. . Moreover, since the content of the glass component is about 1000 ppm or less by weight, abnormal particles do not grow even if fired at a sufficiently high temperature. According to the experiments conducted by the present inventors, the apparent dielectric constant ε was improved by about 1.4 times by the increase of the firing temperature, and the breakdown voltage was 1.3 at the minimum value.
Doubled. These significant improvements in characteristics are due to the fact that the crystal grains have a uniform grain size, no abnormal grain growth occurs, and the variation in the thickness of the insulating layer is small.

[0007]

EXAMPLES Examples of the present invention will be described below. First, as raw materials, SrCO ₃ , CaCO ₃ , MgCO ₃ , T
io ₂ and rare earth are prepared respectively and are shown in Tables 1 and 2 below.
No. in the table Each powder was weighed and wet-mixed in a ball mill for about 8 hours so that a porcelain having a composition ratio shown in 1-27 was obtained. A ball of partially stabilized zirconia was used for the boulder of the ball mill to prevent the glass component from being mixed into the raw material.

The obtained slurry was dried and granulated, and 1150
It was calcined at ℃ for 2 hours. To this calcined raw material, SiO ₂ powder as a glass component was added in a predetermined amount (weight ratio) shown in Tables 1 and 2, and 6% by weight of vinyl acetate resin as a binder and water were further added and wet-mixed and ground. went. After dehydration, the particles were sized with a 50 mesh Saran sieve and
At a pressure of 0 kg / cm ² , the diameter is 10 mm and the thickness is 0.35.
It was formed into a disk shape of mm. Then, these disc-shaped molded bodies were subjected to a degreasing treatment at 1150 ° C. for 2 hours, and subsequently, at 1370 to 14 in a reducing atmosphere of 97% nitrogen and 3% hydrogen.
Baking was performed at 00 ° C. for 5 hours or more.

Then, on the surface of the obtained porcelain body, (A) Bi ₂ O ₃ : 48% by weight, CuO: 2% by weight, varnish: 50% by weight (B) Pb ₃ O ₄ : 45% by weight, MnO ₂ : 5% by weight, resin varnish: 50% by weight (C) Bi ₂ O ₃ : 48% by weight, MnO ₂ : 2% by weight, resin varnish: 50% by weight , In the air 112
It was fired at 0 ° C. for 2 hours to make the crystal grain boundaries an insulator.

Silver paste was applied to both surfaces of the thus obtained porcelain body and baked at 800 ° C. for 30 minutes to form electrodes, which were used as capacitors for evaluation. Tables 1 and 2 show the results of measuring the apparent permittivity ε, the dielectric loss DF, the average of breakdown voltage (kV / mm) and the minimum of the obtained capacitors. The samples marked with * in the sample numbers are outside the scope of the present invention. Further, Sample No. 12 had a low breakdown voltage and exhibited characteristics as a varistor.

A micrograph of the surface of each porcelain body showed that the glass component was 1000 ppm or less. Sample No. 1
~ 4, 8-11, 13, 16-21,
It was observed that the small crystal grains grew almost uniformly.

[0012]

[Table 1]

[0013]

[Table 2]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigeki Nishiyama 2 26-10 Tenjin Tenjin, Nagaokakyo, Kyoto Prefecture Murata Manufacturing Co., Ltd.

Claims (1)

[Claims] _{1. A} (Sr ₁ -XYZ Ca _X Mg _Y M _Z ) TiαO in a SrTiO ₃ -based grain boundary insulating semiconductor ceramic composition in which the average grain size of the crystal grains is 10 μm or less and the maximum grain size is 20 μm or less. ₃ includes crystal grains having a composition of ₃ , provided that the non-stoichiometric values of X, Y, Z and α are X ≦ 0.50, Y ≦ 0.20, 0.002 ≦
Z ≦ 0.02, 0.990 ≦ α ≦ 1.02, and M is an additive such as Y, La, Ce, Gd, Dy, Ho, Er which is converted into a semiconductor by controlling the valence. A grain boundary insulating semiconductor porcelain composition comprising a glass component in an amount of about 1000 ppm or less in weight ratio to a raw material.