JP2934388B2 - Manufacturing method of semiconductor porcelain - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of manufacturing a semiconductor ceramic mainly composed of SrTiO ₃ which is used in the capacitor and a varistor.

[0002]

2. Description of the Related Art In a conventional typical method for producing a semiconductor ceramic mainly composed of SrTiO ₃ , SrCO ₃ and Tr
The mixture with TiO ₂ is calcined to make SrTiO ₃ in advance,
Y for this _{SrTiO 3, La, Ce, Nb} , T
A molded body was prepared from a material to which a valence controlling agent (semiconductor agent) composed of a metal oxide such as a and W and other additives were added, and the molded body was fired.

[0003]

When a grain boundary insulating type capacitor or varistor is manufactured using semiconductor porcelain, in order to obtain good electrical characteristics, it is necessary to promote the formation of a semiconductor and reduce the electrical resistance in the grains. It is necessary to be sufficiently low and to distribute the load with as uniform a particle as possible. In order to promote the former semiconductor, it is effective to increase the addition amount of the valence controlling agent. However, even if the addition amount is simply increased, the amount of solid solution in the SrTiO ₃ crystal grains is limited by the conventional method. Yes,
Not only did the intragranular resistance not become sufficiently low, but also excessive additives segregated at the grain boundaries, hindering the insulation of the grain boundaries and lowering the withstand voltage. Further, in order to make the crystal grain size of the sintered porcelain uniform, the particle size distribution of the SrTiO ₃ powder needs to be fine and sharp. And was difficult to control.

Accordingly, an object of the present invention is to provide a method of manufacturing a semiconductor porcelain capable of making the crystal grain size of the porcelain uniform and suppressing variations in characteristics.

[0005]

SUMMARY OF THE INVENTION In order to achieve the above-mentioned object, the present invention provides a compound of Y and Ti, a compound of La and Ti, and a compound of Ce and Y with respect to a main component material containing at least SrCO ₃ and TiO _2. A step of preparing a semiconductor porcelain raw material to which at least one valence controlling agent among Ti compounds is added, calcining the semiconductor porcelain raw material, and forming a molded body containing the calcined porcelain raw material And a step of firing the compact at a temperature higher than the temperature of the calcining step. The valence controlling agent may be at least one of a compound of Nb and Sr, a compound of Ta and Sr, and a compound of W and Sr. Further, a compound of Y and Ti as a valence controlling agent, La
Both Ti and Ti compounds and Ce and Ti compounds and at least one of Nb and Sr compounds, Ta and Sr compounds and W and Sr compounds can be used. Further, CaCO ₃ can be added as described in the second, fourth and sixth aspects.

[0006]

According to the method of the present invention, the additive substance is Ti or S constituting SrTiO ₃ crystal.
Since it is combined with r, a semiconductor porcelain having a low electric resistance can be obtained by easily forming a solid solution in the crystal during the synthesis process and exhibiting a valence controlling effect corresponding to the added amount. Further, the added Ti compound or Sr compound has an effect of suppressing grain growth of the synthetic powder, and has a fine and sharp particle size distribution that is stable with respect to fluctuations in temperature distribution and calcination conditions during calcination. Is easily obtained, and when this is fired, a semiconductor ceramic having a uniform particle size can be obtained. In addition, when CaCO ₃ is added, varistor characteristics can be obtained.

[0007]

First Embodiment Next, a method of manufacturing a capacitor according to a first embodiment of the present invention will be described. In order to obtain a semiconductor ceramic raw material, S as a main component for obtaining SrTiO ₃
Compounds of rCO ₃ (strontium carbonate) and TiO ₂ (titanium oxide), Y (yttrium) and La (lanthanum) as valence controlling agents (semiconductors), and Ce (cerium) and Ti (titanium) A certain Y ₂ Ti
₂ O ₇ , La ₂ Ti ₂ O ₇ , CeTiO ₄ and Y ₂ O ₃ as a valence controlling agent of a comparative example were prepared, and these were weighed to have the composition shown in Table 1 below.

Table 1 Sample No. SrCO ₃ TiO ₂ Y ₂ Ti ₂ O ₇ La ₂ Ti ₂ O ₇ CeTiO ₄ Y ₂ O ₃ 1 49.9 49.9 0.05 2 49.9 49.9 0.05 3 49.9 49.9 0.14 49.9 49.9 0.025 0.025 5 49.9 49.9 0.025 0.056 49.9 49.9 0.015 0.010 0.057 49.9 50.0 0.05 Each component is shown in molar part.

Next, the raw material powder of each sample was mixed with a wet pot mill and then dried. Next, the mixed powder was calcined in the air (in an oxidizing atmosphere) at 1200 ° C. for 2 hours.

Next, as a sintering aid, a mixture of the main component obtained by calcination and the valence controlling agent is in a ratio of 0.2 mol part to 100 mol part of Sr (strontium). added a SiO _2, which was dried again after pulverization and mixing in a wet pot mill.

Next, 10% by weight of an aqueous solution of polyvinyl alcohol as an organic binder is added to the pulverized mixture, mixed and granulated, and the granulated product is molded under a pressure of 1 ton / cm ² to have a diameter of 10 mm and a thickness of 10 mm. A disc-shaped molded body having a thickness of 0.5 mm was obtained. Next, the compact is placed in a furnace and placed in a H ₂ + N ₂ mixed gas atmosphere (non-oxidizing atmosphere or reducing atmosphere) of H ₂ : N ₂ = 1.5: 98.5 at a volume ratio of 1420.
SrTi as shown in FIG.
A grain boundary insulating semiconductor porcelain 1 containing O ₃ as a main component was obtained.

Next, a known paste component is added to Bi ₂ O ₃ (bismuth oxide) as a grain boundary insulating agent to form a paste.
This was applied to the surface of the porcelain 1 to form a paste layer 2 as shown in FIG.
Baking was performed at 00 ° C. for 2 hours, and Bi ₂ O ₃ was diffused into the porcelain 1 to form a grain boundary insulating layer. The porcelain 1a thus obtained is composed of crystal grains 10 and a grain boundary insulating layer 11, as shown in principle in FIG.

Next, as shown in FIG. 3, a conductive paste (silver paste) is applied to a pair of main surfaces of the sintered body 1a.
The first and second electrodes 3 and 4 were formed by baking at ℃, and the capacitors of each sample were completed. In the case of the comparative example of Sample No. 7, Y ₂ O ₃ as a valence controlling agent was added to the calcined raw material together with SiO ₂ . In addition, each sample was made 100 pieces.

Next, the capacitances C of the capacitors of Sample Nos. 1 to 7, the variation in the capacitance C, the dielectric loss tan δ, and the dielectric breakdown voltage BDV were measured. The capacitance C and the dielectric loss tan δ were measured under the conditions of 25 ° C., a frequency of 1 kHz, and a voltage of 1 V. The variation of the capacitance C was determined according to the following equation. Variation = (standard deviation of capacitance C / average value of capacitance C) × 100 (%)

Table 2 Sample No. C (nF) Variation of C (%) tan δ (%) BDV (V) 154.3.85 0.56 353 2 53.2 7.65 0.62 308 3 55.5 6.02 0.71 278 4 53.2 5.08 0.79 298 5 54.8 4.62 0.83 315 6 53.8 6.20 0.57 306 7 55.9 9.63 0.97 211

As is clear from the comparison between the samples Nos. 1 to 6 according to the present invention in Table 2 and the sample No. 7 of the comparative example, according to the present invention, the capacitance value C which is substantially the same as the conventional one is maintained. In addition, the variation can be reduced, the dielectric loss can be reduced, and the dielectric breakdown voltage can be increased.

[0017]

Second Embodiment Next, a method for manufacturing a varistor according to the present invention will be described. In order to manufacture varistors, seven kinds of mixtures of a main component having the same composition as in Table 1 and a valence controlling agent were prepared. Next, each mixture was mixed in a wet pot mill in the same manner as in the first example, and then dried. Next, the mixed powder was calcined in the air (in an oxidizing atmosphere) at 1200 ° C. for 2 hours.

Next, Sr (strontium) 100 in a mixture of the main component obtained by calcination and the valence controlling agent is used.
CaTiO ₃ (calcium titanate) as an additional main component so as to have a ratio of 10 mole parts to mole parts,
Si as a sintering aid so as to have a ratio of 0.2 mole part
O ₂ was added, and the mixture was pulverized and mixed again in a wet pot mill, and then dried to obtain seven samples Nos. 8 to 14 corresponding to Samples Nos. 1 to 7 in the first example.

Next, 5% by weight of an aqueous polyvinyl alcohol solution as an organic binder was added to the pulverized mixture of each sample, mixed and granulated, and the granulated product was added at 1 ton / cm ^2.
To obtain a disk-shaped molded body having a diameter of 10 mm and a thickness of 0.5 mm. Next, the molded body is placed in a furnace in an H ₂ + N ₂ mixed gas atmosphere (non-oxidizing atmosphere or reducing atmosphere) of H ₂ : N ₂ = 1.5: 98.5 in volume ratio.
Sr similar to FIG. 1 made of a sintered body fired at 0 ° C. for 2 hours.
A grain boundary insulating semiconductor porcelain containing CaTiO ₃ as a main component was obtained.

Next, 5 parts by weight of a well-known paste component is added to Na ₂ O (sodium oxide) and mixed to form a homogeneous diffusion composition paste, which is applied to the surface of the porcelain in the same manner as in FIG. A paste layer was formed, and the paste layer was placed in a furnace and baked at 1100 ° C. for 2 hours in the air to diffuse Na ₂ O into the porcelain. As a result, a grain boundary insulating layer is formed, and Na or a Na compound diffuses as a liquid phase at the grain boundaries of the crystal, thereby firmly bonding adjacent particles.

Next, as in FIG. 3, a conductive paste (silver paste) is applied to a pair of main surfaces of the sintered body and baked to form first and second electrodes. A capacitive varistor element, that is, a semiconductor porcelain varistor was completed.

Next, the varistor voltages V of the sample Nos. 8 to 14 were
1 m, the variation of the varistor voltage V1m, the nonlinear coefficient α, and the energy tolerance E were determined. Here, the varistor voltage V1m is a voltage between a pair of electrodes when 1 mA flows between the pair of electrodes of the varistor element. The voltage nonlinear coefficient α is 1 for the varistor element.
It was obtained by the following equation based on the voltage V1m between the pair of electrodes when mA was applied and the voltage V10m between the pair of electrodes when 10 mA was applied. α = 1 / {log (V10m / V1m)} The energy tolerance E is obtained by applying a pulse of the voltage V to the varistor element twice at intervals of 10 seconds to find a voltage V at which the rate of change of the varistor voltage falls within 5%. Determined by the formula. E = 1/2 (CV ² ) (joul) The variation of the varistor voltage was obtained by the following equation. V1m variation = (standard deviation of V1m / average value of V1m) ×
100 (%) The following table shows the measurement results of Samples Nos. 8 to 14.

Table 3 Sample No. V1m (V) Variation (%) of V1m α E (joul) 8 33.2 4.58 10.78 13.5 9 29.8 5.45 10.85 12.5 10 31.5 6.26 11.22 16.0 11 30.8 6.56 10.89 13.0 12 29.3 7.28 11.03 18.5 13 31.5 4.85 10.85 14. 514 27.3 9.79 10.58 7.0

As is apparent from the comparison between the samples Nos. 8 to 13 according to the present invention in Table 3 and the sample No. 14 of the comparative example, according to the present invention, the varistor voltage V1m and the non-linear While maintaining the coefficient α, the variation in the varistor voltage can be reduced, and the energy withstand capability can be greatly improved.

[0025]

Third Embodiment In a capacitor, Nb (niobium), Ta (tantalum), W (tungsten) as a valence controlling agent and an Sr compound can be used to obtain the same operation and effect as in the first embodiment. In order to confirm, Y ₂ Ti ₂ O ₇ , La ₂ Ti ₂ O ₇ , CeT in the first embodiment were used.
iO ₄ and Y ₂ O ₃ are converted to Sr ₂ Nb ₂ O ₇ and Sr ₂ Ta
Seven samples having the compositions shown in the following Table 4 were prepared by substituting ₂ O, SrWO ₄ , and Nb ₂ O ₅ .

Table 4 Sample No. SrCO ₃ TiO ₂ Sr ₂ Nb ₂ O ₇ Sr ₂ Ta ₂ O ₇ SrWO ₄ Nb ₂ O ₅ 15 49.9 49.9 0.05 16 49.9 49.9 0.05 17 49.9 49.9 0.1 18 49.9 49.9 0.025 0.025 19 49.9 49.9 0.025 0.05 20 49.9 49.9 0.015 0.010 0.05 21 50.0 49.9 0.05 The compositions in Table 4 are shown in parts by mole.

A ceramic capacitor mainly composed of SrTiO ₃ was manufactured in the same manner as in the first embodiment except that the composition in Table 1 of the first embodiment was changed to the composition in Table 4, and the same characteristics were obtained. When measured by the method, the results in Table 5 below were obtained.

Table 5 Sample NO. C (nF) Variation of C (%) tan δ (%) BDV (V) 15 51.3 4.35 0.53 365 16 49.8 5.78 0.42 318 17 48.5 4.58 0.62 329 18 50.2 5.08 0.54 345 19 51.5 6.08 0.70 328 20 50.8 6.82 0.47 358 21 55.9 8.28 0.85 206

As apparent from the comparison between the sample Nos. 15 to 20 according to the present invention in Table 5 and the sample No. 21 of the comparative example, the first
The same effect as that of the embodiment can be obtained.

[0030]

Fourth Embodiment In a varistor, even if Nb (niobium), Ta (tantalum), and W (tungsten) are used as Sr compounds as valence controlling agents, the same operation and effects as in the second embodiment can be obtained. For confirmation, the same composition as in Table 4 in the third embodiment was prepared, and Y ₂ Ti ₂ O ₇ , La ₂ Ti ₂ O ₇ and CeTi of the second embodiment were prepared.
O ₄ and Y ₂ O ₃ are converted to Sr ₂ Nb ₂ O ₇ , Sr ₂ Ta ₂ O,
Sample No. 2 corresponding to Sample Nos. 15 to 21 in the same manner as in the second embodiment except that SrWO ₄ and Nb ₂ O ₅ were substituted.
When 2 to 28 porcelain varistors containing SrCaTiO ₃ as a main component were prepared and their characteristics were measured by the same method as in the second embodiment, the results shown in the following Table 6 were obtained.

Table 6 Sample No. V1m (V) V1m variation (%) α E (joul) 22 32.5 5.02 11.28 16.0 23 31.8 6.34 10.89 14.5 24 33.2 7.28 11.35 12.0 25 31.6 5.50 10.81 13.5 26 33.7 6.59 10.96 11.5 27 31.2 4.81 11.05 13. 0 28 29.7 9.83 10.02 7.5

As is apparent from the comparison between the samples Nos. 22 to 27 according to the present invention in Table 6 and the sample No. 28 of the comparative example, the same effect as that of the second embodiment can be obtained by the fourth embodiment. be able to.

[0033]

Fifth Embodiment Sr ₂ Nb ₂ O ₇ as a valence controlling agent of the third embodiment was added to the composition shown in Table 1 of the first embodiment.
Compositions shown in the following Table 7 were prepared in order to confirm that the same effects as in the first example could be obtained even when Sr ₂ Ta ₂ O ₇ and SrWO ₄ were added. In Table 7, the composition is shown in parts by mole.

[0034]

[Table 1]

Sample No. 1 was prepared in the same manner as in the first embodiment except that the composition in Table 1 in the first embodiment was changed to the composition in Table 7.
29 to 35 of SrTiO ₃ as a main component were prepared and their characteristics were measured by the same method as in the first embodiment. The results shown in Table 8 below were obtained.

Table 8 Sample NO. C (nF) Variation of C (%) tan δ (%) BDV (V) 29 51.3 5.55 0.73 323 30 49.2 5.35 0.88 318 31 51.5 5.72 0.82 319 32 50.2 5.28 0.79 332 33 51.8 5.61 0.78 319 34 50.8 5.13 0.75 316 35 55.9 9.25 0.92 278

As apparent from the comparison between the sample Nos. 29 to 34 according to the present invention in Table 8 and the sample No. 35 of the comparative example, the fifth sample
According to this embodiment, the same effect as that of the first embodiment can be obtained.

[0038]

[Sixth Embodiment] In the fifth embodiment, the sample NO.
In order to confirm that a varistor can be produced based on the compositions of Nos. 29 to 34, that is, the valence controlling agent of the second example was further added with Sr ₂ Nb ₂ O ₇ and Sr ₂ Ta.
_In order to confirm that the same effect as in the second embodiment can be obtained even when ₂ O ₇ and SrWO ₄ are added, the same composition as in Table 7 was prepared, and the composition according to Table 1 in the second embodiment was changed. A sample was prepared in the same manner as in the second embodiment except that the composition was changed to that shown in Table 7.
When a porcelain varistor mainly composed of SrCaTiO ₃ of Nos. 36 to 42 was manufactured and its characteristics were measured by the same method as in the second embodiment, the results shown in Table 9 below were obtained.

Table 9 Sample No. V1m (V) Variation (%) of V1m α E (joul) 36 28.2 6.32 11.22 15.37 377.8 7.48 11.06 14.29 38 28.4 6.56 11.35 15.78 39 26.8 6.27 11.33 13.45 40 27.3 6.19 11.43 14.67 41 26.9 6.57 11.25 16. 71 42 31.3 9.32 10.88 8.27

As is clear from the comparison between the sample Nos. 36 to 41 according to the present invention shown in Table 9 and the sample No. 42 of the comparative example, the sixth sample was obtained.
According to this embodiment, the same effect as that of the second embodiment can be obtained.

[0041]

[Modifications] The present invention is not limited to the above-described embodiment, and for example, the following modifications are possible. (1) The main component is not limited to SrTiO ₃ and SrCaTiO ₃ , but ABO ₃ (where A is Sr, Ca, Ba, M
One or more elements of g, and B is one or more elements of Ti and Zr) may be a titanium-strontium-based component. (2) In addition to a Ti compound of Y, La, and Ce and / or a Sr compound of Nb, Ta, and W as a valence controlling agent,
One or a plurality of oxides of W, Ta, Nb and rare earth elements can be used. (3) The amount of the valence controlling agent to be added to 100 mole parts of the main component can be preferably changed in the range of 0.01 to 5.00 mole parts. (4) Al ₂ O ₃ as a sintering aid for porcelain materials;
One or more kinds selected from SiO ₂ , CuO, MnO ₂ , and Ag ₂ O are preferably used in an amount of 0.05 mol% based on 100 mol parts of SrTiO ₃ or the main component composed of ABO ₃ described above.
It can be added in the range of 0.50 mol part. (5) Instead of Bi ₂ O ₃ as an insulating agent at the grain boundary, P
b ₃ O ₄ , B ₂ O _3, and these and Mn
Making a metal oxide paste using one or more kinds selected from metal oxides such as O ₂ , CuO, Tl ₂ O ₃ , Sb ₂ O ₅ , Fe ₂ O ₃ , and applying this to a porcelain Can be. (6) Bi ₂ O ₃ , Pb as grain boundary insulating agent
Instead of applying a paste such as ₃ O ₄ , B ₂ O ₃ , MnO ₂ , CuO, etc., it can be mixed with the porcelain raw material before firing. In this case, a step of performing heat treatment in an oxidizing atmosphere after firing (re-oxidation processing step) is provided. (7) The manufacturing conditions of the porcelain can be variously changed.
For example, calcining is performed at 1000 to 1200 ° C. for 1 to 5 hours, and firing in a non-oxidizing atmosphere is performed at 1300 to 1 hour.
The temperature is set to 500 ° C. for 1 to 5 hours, and the reoxidation treatment or the diffusion treatment of the grain boundary insulating agent after firing is performed at 800 to 1300.
° C, for 1 to 5 hours. (8) CaCO ₃ added at the time of forming a varistor may be added to SrCO ₃ and TiO ₂ before calcination. (9) The present invention can also be applied to a case where a laminate obtained by printing a conductive paste on a porcelain green sheet (raw sheet) and laminating the same to produce a laminated element.

[Brief description of the drawings]

FIG. 1 is a front view showing a porcelain sintered body according to an embodiment of the present invention.

FIG. 2 is a front view showing the sintered body of FIG. 1 coated with a paste of a diffusion composition.

FIG. 3 is a front view showing a completed capacitor.

FIG. 4 is a sectional view showing the internal structure of porcelain in principle.

[Explanation of symbols]

 1a Porcelain 3, 4 electrodes

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kiyoshi Tanaka 6-16-20 Ueno, Taito-ku, Tokyo Taiyo Yuden Co., Ltd. (58) Field surveyed (Int. Cl. ⁶ , DB name) H01G 4 / 12

Claims (6)

(57) [Claims] 1. A compound of Y and Ti, a compound of La and Ti, and at least one valence controlling agent of a compound of Ce and Ti with respect to a main component material containing at least SrCO ₃ and TiO _2. Preparing the added semiconductor porcelain raw material, calcining the semiconductor porcelain raw material, forming a molded body containing the calcined porcelain raw material, and setting the molded body higher than the temperature of the calcining step Baking at a temperature. 2. A compound containing Y and Ti, a compound containing La and Ti, and at least one valence controlling agent among compounds containing Ce and Ti are added to a main component material containing at least SrCO ₃ and TiO _2. Preparing the added semiconductor ceramic raw material and calcining the semiconductor ceramic raw material; adding at least CaCO ₃ to the calcined ceramic raw material to form a molded body; Baking at a temperature higher than the temperature of the step. 3. A compound of Nb and Sr, a compound of Ta and Sr based on a main component material containing at least SrCO ₃ and TiO _2.
Preparing a semiconductor porcelain raw material to which at least one kind of valence controlling agent among compounds of W and Sr is added, and calcining the semiconductor porcelain raw material; A method for manufacturing a semiconductor ceramic, comprising: a step of forming a molded body; and a step of firing the molded body at a temperature higher than the temperature of the calcining step. 4. A compound of Nb and Sr, Ta and Sr based on a main component material containing at least SrCO ₃ and TiO _2.
And a step of calcining the semiconductor ceramic raw material to which at least one valence controlling agent of the compound of W and Sr is added, and calcining the semiconductor ceramic raw material. A method for manufacturing a semiconductor ceramic, comprising: a step of forming a compact by adding CaCO ₃ ; and a step of firing the compact at a temperature higher than the temperature of the calcining step. 5. A valence control agent of at least one of a compound of Y and Ti, a compound of La and Ti, and a compound of Ce and Ti with respect to a main component material containing at least SrCO ₃ and TiO _2. Preparing a semiconductor porcelain material to which a compound of Nb and Sr, a compound of Ta and Sr, and at least one valence controlling agent among compounds of W and Sr are added, and calcining the semiconductor porcelain material; A method for manufacturing a semiconductor porcelain, comprising: a step of forming a molded body containing the calcined porcelain raw material; and a step of firing the molded body at a temperature higher than the temperature of the calcining step. 6. A valence control agent of at least one of a compound of Y and Ti, a compound of La and Ti, and a compound of Ce and Ti with respect to a main component material containing at least SrCO ₃ and TiO _2. Preparing a semiconductor porcelain material to which a compound of Nb and Sr, a compound of Ta and Sr, and at least one valence controlling agent among compounds of W and Sr are added, and calcining the semiconductor porcelain material; A semiconductor comprising: a step of adding at least CaCO ₃ to the calcined porcelain raw material to form a molded body; and a step of firing the molded body at a temperature higher than the temperature of the calcining step. Method of manufacturing porcelain.