JPH08124782A - Manufacture of semiconductor ceramic - Google Patents

Abstract

PURPOSE: To make crystal grain diameter uniform and restrain variation of characteristics, by calcinating and molding semiconductor porcelain material wherein specific valence control agent is added to main component material containing at least SrCO3 and TiO2 , and baking the object at a temperature higher than the calcinating temperature. CONSTITUTION: Semiconductor porcelain material is prepared wherein at least one kind of valence control agent out of compound of Y and Ti, compound of La and Ti, and compound of Ce and Ti is added to the main component material containing at least SrCO3 and TiO2 . The semiconductor ceramic material is calcinated, and then a molded object containing the calcinated ceramic material is formed. The molded object is baked at a temperature higher than the calcinating temperature. As the valence control agent, at least one out of compound of Nb and Sr, compound of Ta and Sr, and compound of W and Sr can be used. Thereby the additive material easily forms solid solution in crystal, so that semiconductor ceramic wherein electric resistance is low and grain diameter is uniform can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor porcelain containing SrTiO ₃ as a main component used in capacitors and varistors.

[0002]

2. Description of the Related Art In a conventional typical manufacturing method of a semiconductor ceramic containing SrTiO ₃ as a main component, SrCO ₃ and T
The mixture with iO ₂ is calcined to make SrTiO ₃ in advance,
Y, La, Ce, Nb, T for this SrTiO ₃
A molded body was made by adding a valence control agent (semiconductor agent) composed of a metal oxide such as a and W and other additives, and the molded body was fired.

[0003]

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

Therefore, it is an object of the present invention to provide a method of manufacturing a semiconductor porcelain which can make the crystal grain size of the porcelain uniform and suppress variations in characteristics.

[0005]

The present invention for achieving the above object provides a compound of Y and Ti, a compound of La and Ti, and Ce with respect to a main component raw material containing at least SrCO ₃ and TiO _2. A step of preparing a semiconductor porcelain raw material to which at least one valence control agent of Ti compounds is added, calcination of the semiconductor porcelain raw material, and a step of forming a compact containing the calcinated porcelain raw material And a step of firing the molded body at a temperature higher than the temperature of the calcination step, the present invention relates to a method for manufacturing a semiconductor porcelain. The valence control agent may be at least one of Nb and Sr compounds, Ta and Sr compounds, and W and Sr compounds. Further, as described in claim 5, a compound of Y and Ti as a valence control agent, La
It is possible to use both at least one of the compounds of Ti and Ti and the compounds of Ce and Ti, and at least one of the compounds of Nb and Sr, the compounds of Ta and Sr, and the compounds of W and Sr. Further, as shown in claims 2, 4, and 6, CaCO ₃ can be added.

[0006]

According to the method of the invention of each claim, 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 to exert a valence control effect corresponding to the added amount. Further, the added Ti compound or Sr compound has an effect of suppressing the grain growth of the synthetic powder, and has a fine and sharp particle size distribution which is stable and stable against changes in temperature distribution during calcination and changes in calcination conditions. Can be easily obtained, and when this is fired, a semiconductor ceramic having a uniform grain size can be obtained. When CaCO ₃ is added as described in claims 2, 4 and 6, varistor characteristics are 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 porcelain raw material, S as a main component for obtaining SrTiO ₃
rCO ₃ (strontium carbonate) and TiO ₂ (titanium oxide), Y (yttrium), La (lanthanum), and a compound of Ce (cerium) and Ti (titanium) as a valence control agent (semiconductor agent) A certain Y ₂ Ti
₂ O ₇ , La ₂ Ti ₂ O ₇ and CeTiO ₄ and Y ₂ O ₃ as a valence control agent of Comparative Example were prepared and weighed so as 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 0.1 4 49.9 99.9 0.025 0.025 5 49.9 49.9 0.025 0.05 6 49.9 49.9 0.015 0.01 0 .05 7 49.9 50.0 0.05 Each component is shown in parts by mole.

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

Next, as a sintering aid, a ratio of 0.2 parts by mole to 100 parts by mole of Sr (strontium) in the mixture of the main component and the valence control agent obtained by calcination is used as a sintering aid. Of SiO ₂ was added, and this was again ground and mixed in a wet pot mill and then dried.

Next, 10% by weight of an aqueous polyvinyl alcohol solution was added as an organic binder to the crushed mixture, mixed and granulated, and the granulated product was molded at a pressure of 1 ton / cm ² to have a diameter of 10 mm and a thickness of 10 mm. A disk-shaped molded body having a size of 0.5 mm was obtained. Next, this compact was put in a furnace and put in a H ₂ + N ₂ mixed gas atmosphere (non-oxidizing atmosphere or reducing atmosphere) of H ₂ : N ₂ = 1.5: 98.5 in a volume ratio of 1420.
SrTi shown in Fig. 1 consisting of a sintered body after firing at ℃ for 2 hours.
A grain boundary insulation type semiconductor ceramic 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 prepare a paste,
This is applied to the surface of the porcelain 1 to form a paste layer 2 as shown in FIG.
After firing at 00 ° C. for 2 hours, Bi ₂ O ₃ was diffused in 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 the pair of main surfaces of the sintered body 1a, and 800
The first and second electrodes 3 and 4 were formed by baking at ° C to complete the capacitors of the respective samples. In the case of the comparative example of sample No. 7, Y ₂ O ₃ as a valence control agent was added to the raw material after calcination together with SiO ₂ . In addition, 100 samples were made for each sample.

Next, the capacitance C of the capacitors of sample Nos. 1 to 7, the variation of 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., frequency 1 kHz and voltage 1V. Further, the variation of the capacitance C was obtained according to the following equation. Variation = (standard deviation of capacitance C / average value of capacitance C) x 100 (%)

Table 2 Sample NO. C (nF) C Variation (%) tan δ (%) BDV (V) 1 54.3 4.85 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 can be seen from the comparison between the sample Nos. 1 to 6 according to the present invention and the sample No. 7 of the comparative example in Table 2, according to the present invention, the substantially same capacitance value C 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 of manufacturing a varistor according to the present invention will be described. In order to manufacture a varistor, seven types of mixtures of a main component having the same composition as in Table 1 and a valence control agent were prepared. Next, each mixture was mixed in a wet pot mill as in the first example, and then dried. Next, this mixed powder was calcined in the air (in an oxidizing atmosphere) at 1200 ° C. for 2 hours.

Next, Sr (strontium) 100 in the mixture of the main component obtained by calcination and the valence control agent is added.
CaTiO ₃ (calcium titanate) as an additional main component so that the ratio of 10 parts by mole to the parts by mole,
Si as a sintering aid in a proportion of 0.2 parts by mole
O ₂ was added, and the mixture was pulverized and mixed again in the wet pot mill and then dried to obtain seven samples No. 8 to 14 corresponding to the sample 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 crushed mixture of each sample, mixed and granulated, and the granulated product was 1 ton / cm ^2.
Was molded under pressure to obtain a disk-shaped molded body having a diameter of 10 mm and a thickness of 0.5 mm. Next, this molded body was placed in a furnace and placed in a H ₂ + N ₂ mixed gas atmosphere (non-oxidizing atmosphere or reducing atmosphere) having a volume ratio of H ₂ : N ₂ = 1.5: 98.5.
Sr similar to that in FIG. 1 composed of a sintered body after firing at 0 ° C. for 2 hours
A grain boundary insulation type semiconductor ceramic containing CaTiO ₃ as a main component was obtained.

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

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, and sample Nos. 8 to 14 are prepared. A capacitive varistor element, that is, a semiconductor porcelain varistor was completed.

Next, the varistor voltage V of sample Nos. 8 to 14 was measured.
The variation of 1 m, the varistor voltage V1 m, the non-linear coefficient α, and the energy tolerance E were obtained. Here, the varitor voltage V1m is a voltage between the pair of electrodes when 1 mA is applied between the pair of electrodes of the varistor element. The voltage nonlinear coefficient α is 1 for the varistor element.
It was determined by the following formula based on the voltage V1m between the pair of electrodes when a current of mA was applied and the voltage V10m between the pair of electrodes when a current of 10 mA was applied. α = 1 / {log (V10m / V1m)} Energy tolerance E is obtained by applying a pulse of voltage V twice to the varistor element at intervals of 10 seconds to obtain voltage V within which the rate of change in varistor voltage is within 5%. It was decided by the formula. E = 1/2 (CV ² ) (joul) The variation of the varistor voltage was calculated by the following formula. Variation of V1m = (standard deviation of V1m / average value of V1m) ×
100 (%) The following table shows the measurement results of sample Nos. 8-14.

Table 3 Sample No. V1m (V) V1m Variation (%) 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. 5 14 27.3 9.79 10.58 7.0

As is clear from the comparison between the sample 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-linearity which are substantially the same as those of the conventional one are obtained. While maintaining the coefficient α, it is possible to reduce variations in the varistor voltage and significantly improve the energy tolerance.

[0025]

[Third Embodiment] In a capacitor, the same effects as those of the first embodiment can be obtained with Nb (niobium), Ta (tantalum), W (tungsten) and Sr compounds as valence control agents. To confirm, Y ₂ Ti ₂ O ₇ , La ₂ Ti ₂ O ₇ and CeT in the first embodiment are used.
iO ₄ , Y ₂ O ₃ to Sr ₂ Nb ₂ O ₇ , Sr ₂ Ta
Seven samples having the compositions shown in the following Table 4 in which ₂ O, SrWO ₄ , and Nb ₂ O ₅ were substituted were prepared.

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 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 0.01 0 .05 21 50.0 49.9 0.05 The composition in Table 4 is shown in parts by mole.

A porcelain capacitor containing SrTiO ₃ as a main component was prepared in the same manner as in the first embodiment except that the composition shown in Table 1 of the first embodiment was changed to the composition shown in Table 4, and the characteristics were the same. When measured by the method, the results shown in Table 5 below were obtained.

Table 5 Sample NO. C (nF) C variation (%) 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 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 can be seen from the comparison of sample Nos. 15 to 20 according to the present invention in Table 5 with sample No. 21 of the comparative example,
The same effect as that of the embodiment can be obtained.

[0030]

[Fourth Embodiment] In the varistor, even if Nb (niobium), Ta (tantalum), and W (tungsten) as valence control agents are used as Sr compounds, the same effects as those of the second embodiment can be obtained. For confirmation, the same composition as in Table 4 in the third example was prepared, and Y ₂ Ti ₂ O ₇ , La ₂ Ti ₂ O ₇ , CeTi in the _second example were prepared.
O ₄ , Y ₂ O ₃ are replaced with 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 replaced.
A porcelain varistor containing SrCaTiO ₃ of 2 to 28 as a main component was prepared, and its characteristics were measured by the same method as in the second embodiment. The results shown in Table 6 below 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 clear from the comparison between the sample 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 example can be obtained by the fourth embodiment. be able to.

[0033]

[Fifth Embodiment] In the composition shown in Table 1 of the first embodiment, Sr ₂ Nb ₂ O ₇ as a valence control agent of the third embodiment,
The compositions shown in the following Table 7 were prepared in order to confirm that the same effect as that of the first example can be obtained even if Sr ₂ Ta ₂ O ₇ and SrWO ₄ are 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 shown in Table 1 in the first embodiment was changed to the composition shown in Table 7.
When 29 to 35 porcelain capacitors containing SrTiO ₃ as a main component were made 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) C variation (%) 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 55.9 925 0.92 278

As can be seen from the comparison of the sample Nos. 29 to 34 according to the present invention in Table 8 with the sample No. 35 of the comparative example,
The same effect as that of the first embodiment can be obtained by the embodiment.

[0038]

[Sixth Embodiment] The sample No. of Table 8 in the fifth embodiment.
To confirm that varistors can be made based on the compositions of 29-34, ie the valency control agent of the second example is further supplemented with Sr ₂ Nb ₂ O ₇ , Sr ₂ Ta.
_In order to confirm that the same effect as in the second embodiment can be obtained by adding ₂ O ₇ and SrWO ₄ , the same composition as in Table 7 was prepared, and the composition according to Table 1 in the second embodiment was prepared. Samples were prepared in the same manner as in the second embodiment except that the composition shown in Table 7 was changed.
When a porcelain varistor containing SrCaTiO _{3 of} NO. 36 to 42 as a main component was prepared 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) V1m variation (%) α E (joul) 36 28.2 6.32 11.22 15.37 37 37 27.8 6.48 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 can be seen from the comparison of sample Nos. 36 to 41 according to the present invention in Table 9 with sample No. 42 of the comparative example,
The same effect as that of the second embodiment can be obtained by this embodiment.

[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, B is one or more elements of Ti and Zr), and may be a titanium strontium-based component. (2) In addition to the Ti compound of Y, La and Ce and / or the Sr compound of Nb, Ta and W as a valence control agent,
One or more kinds of oxides of W, Ta, Nb and rare earth elements can be used. (3) The addition amount of the valency control agent to 100 parts by mol of the main component can be changed preferably in the range of 0.01 to 5.00 parts by mol. (4) Al ₂ O ₃ as a sintering aid for porcelain materials,
One or more selected from SiO ₂ , CuO, MnO ₂ and Ag ₂ O is preferably added to the main component consisting of 100 parts by mole of SrTiO ₃ or ABO ₃ mentioned above.
It can be added in the range of 0.50 mol part. (5) Instead of Bi ₂ O ₃ as an insulating agent for grain boundaries, P
The use of b ₃ O ₄ and B ₂ O _3, as well as these and Mn
Forming 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 it to porcelain. You can (6) Bi ₂ O ₃ , Pb as grain boundary insulating agent
Instead of applying ₃ O ₄ , B ₂ O ₃ , MnO ₂ , CuO, etc. with a paste, 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 (reoxidation treatment step) is provided. (7) The manufacturing conditions of porcelain can be variously changed.
For example, calcination is performed in the range of 1000 to 1200 ° C. for 1 to 5 hours, and calcination in a non-oxidizing atmosphere is 1300 to 1
The temperature is set to 500 ° C. for 1 to 5 hours, and the reoxidation treatment after firing or the diffusion treatment of the grain boundary insulating agent is performed at 800 to 1300.
The temperature may be 1 ° C for 1 to 5 hours. (8) CaCO ₃ added when making a varistor may be added to SrCO ₃ and TiO ₂ before calcination. (9) The present invention can be applied to a case where a porcelain green sheet (green sheet) on which a conductive paste is printed is laminated and fired to form a laminated element.

[Brief description of drawings]

FIG. 1 is a front view showing a porcelain sintered body according to an example 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 in principle the internal structure of a porcelain.

[Explanation of symbols]

 1a Porcelain 3, 4 electrodes

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshika Tanaka 6-16-20 Ueno Taito-ku, Tokyo Inside Taiyo Induction Co., Ltd.

Claims (6)

[Claims] 1. 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 is added to a main component material containing at least SrCO ₃ and TiO _2. A step of preparing the added semiconductor porcelain raw material, calcination of the semiconductor porcelain raw material, a step of forming a compact containing the calcined porcelain raw material, and a temperature of the compact higher than the calcination step And a step of firing at a temperature. 2. 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 is added to a main component material containing at least SrCO ₃ and TiO _2. A step of preparing the added semiconductor porcelain raw material, calcination of the semiconductor porcelain raw material, a step of adding at least CaCO ₃ to the calcinated porcelain raw material to form a compact, and the calcination of the compact And a step of firing at a temperature higher than the temperature of the step. 3. A compound of Nb and Sr, Ta and Sr with respect to a main material containing at least SrCO ₃ and TiO _2.
A semiconductor porcelain raw material to which at least one valence control agent of the compound of No. 1 and a compound of W and Sr is added, and calcining the semiconductor porcelain raw material, and including the calcined porcelain raw material A method of manufacturing a semiconductor porcelain, 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 calcination step. 4. A compound of Nb and Sr, Ta and Sr with respect to a main component material containing at least SrCO ₃ and TiO _2.
And a valence control agent of at least one of the compounds of W and Sr are added to prepare a semiconductor porcelain raw material, and the semiconductor porcelain raw material is calcined; A method of manufacturing a semiconductor porcelain, 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 calcination 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 raw material containing at least SrCO ₃ and TiO _2. A step of preparing a semiconductor porcelain raw material to which a compound of Nb and Sr, a compound of Ta and Sr, and at least one valence control agent of compounds of W and Sr are added, and calcination of the semiconductor porcelain raw material; A method of manufacturing a semiconductor porcelain, comprising: a step of forming a formed body containing the calcined porcelain raw material; and a step of firing the formed body at a temperature higher than the temperature of the calcination 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 raw material containing at least SrCO ₃ and TiO _2. A step of preparing a semiconductor porcelain raw material to which a compound of Nb and Sr, a compound of Ta and Sr, and at least one valence control agent of compounds of W and Sr are added, and calcination of the semiconductor porcelain raw material; A semiconductor comprising: a step of forming a compact by adding at least CaCO ₃ to the calcined porcelain raw material; and a step of firing the compact at a temperature higher than the temperature of the calcining step. Method of manufacturing porcelain.