JPH01232701A - Manufacture of positive characteristic semiconductor porcelain - Google Patents

Abstract

PURPOSE:To manufacture a low resistance positive characteristic semiconductor porcelain at low cost by a method wherein a barium titanate calcined powder is heated up within a specific temperature range, it is then quickly cooled down at a specific cooling speed, it is pulverized, and its molded body is sintered in the atmospheric air. CONSTITUTION:A mixing process in which raw material powder is mixed, a calcination process wherein the mixed powder is calcined and a barium titanate calcined powder is mainly alloyed, a heat treatment process in which said barium titanate calcined powder is heated in the temperature range of 1000-1250 deg.C and then the calcined powder is cooled down quickly at the cooling speed of 500 deg.C/hr. or above, a molding process wherein the heat-treated barium titanate calcined powder is pulverized and formed into a molded body of the prescribed shape, and a sintering process, in which the molded body is sintered in the atmospheric air, are conducted successively. To be more precise, the oxygen defect concentration in the powder can be improved by conducting the above-mentioned heat-treatment process, and the oxygen defect can be confined in a bulk by molding the calcined powder containing high concentration of oxygen defect and obtained as above, and by sintering it in the atmospheric air.

Description

[Detailed Description of the Invention] [Industrial Application Field 1] The present invention relates to a method for manufacturing a special semiconductor porcelain (PTC thermistor) characterized by barium titanate. The present invention relates to a method for producing positive characteristic semiconductor porcelain, which allows a desired resistance value to be obtained in a compact shape, expands the degree of freedom in design, and is expected to reduce costs by downsizing applied products.

INDUSTRIAL APPLICATION This invention is utilized for an overcurrent protection device (prower resistor), a motor starting element, a temperature sensor, a self-organizing system heating element, etc.

[Prior Art] As shown in Fig. 4, the conventional general method for manufacturing positive characteristic semiconductor porcelain uses barium carbonate (BaCO2) and titanium dioxide (Ti12) as main raw materials, and in addition, Y, La, and Nb.
Barium titanate (BaTi
O3) This is a method in which powder is pulverized, molded using it, and then fired in the atmosphere.

Also, attempts have been made to produce conductor porcelain using the coprecipitation method or the alcoyacid method.

Furthermore, 0.01 to 0.3 mol% of excess BaO is added to the main component of B a'r I O3'9 and fired in a neutral gas atmosphere such as nitrogen or argon to produce semiconductor porcelain with positive characteristics. The manufacturing method of
Publication No. 68). In addition, 0.3 to 10.0% of 5if2 is added, firing is performed in the above-mentioned neutral gas atmosphere, and then earth-zinc is performed in an oxidizing atmosphere slightly lower than the firing temperature to produce positive characteristic semiconductor porcelain. A method is also known (Japanese Patent Publication No. 42-1134).

[Problem to be Solved by the Invention 1] However, no matter which method is used, the normal temperature specific resistance of this semiconductor ceramic is limited to 5 Ω·cm.

In particular, 1yiri Special Publication No. 1268/1973 and No. 4
In Publication No. 2-1134, the specific resistance at 25°C is 10
( ) Ω・cm or more, which is roughly large.

Therefore, in order to obtain a PTC thermistor with low resistance, it is necessary to increase the size and reduce the element thickness, or to use a plurality of thermistors connected in parallel. Therefore, when used as an overcurrent protection device or a motor starting element, there is a problem that malfunction may occur due to self-heating caused by the voltage drop. Furthermore, in this case, the element has to be large in size, and the space required during design is 1. I
The amount of Ir was large, leading to an even greater cost increase of Ir4.

The present invention overcomes the above problems, and
The object of the present invention is to provide a method for manufacturing positive characteristic semiconductor porcelain that can inexpensively achieve a specific resistance lower than 11.

[Means for Solving the Problems] The method for manufacturing a positive characteristic semiconductor TA device of the first invention includes a mixing step V for mixing raw material powders, and calcination of the mixed powder mixed in the mixing step. A calcination step for synthesizing a barium titanate calcined powder and a barium titanate calcined powder milled by the above calcination step to i ooo ~ 1250
℃ heat treatment step, followed by rapid cooling at a cooling rate of 500℃/hour or more, and molding, in which the treated barium titanate calcined powder is pulverized and molded into a predetermined shape. and a firing step of firing the molded body of the fusuma in the atmosphere, which is considered to be v1 characteristic.

The second invention also includes a mixing step of mixing raw material powders, and a calcination step of primarily synthesizing barium titanate calcined powder by calcining the mixed powder mixed in the mixing step,
A method for producing a positive characteristic semiconductor comprising: a molding step of pulverizing the calcined barium titanate powder to form a molded body of a predetermined shape; and a firing step of firing the eroded molded body in the atmosphere. In the calcination step, before the calcination step, the barium titanate calcined powder or the molded material is heated in one of a neutral atmosphere, a reducing atmosphere, and a III element-deficient atmosphere containing 5% by volume or less of oxygen. Body 8o.

Pretreatment in the temperature range ~1250°C! l
It is characterized by carrying out science and engineering culm.

By the way, there are various theories regarding the conduction mechanism of the PTC element, such as hopping conduction of 3D electrons, but the general theory is that it is based on the generation of free electrons accompanying the generation of oxygen defects.

And the resistance of the PTC element is bulk and boundary
It is expressed by the sum of the resistances of y (grain boundaries), but in general, the resistance of the bulk is dominant at temperatures below Tl, and the resistance of grain boundaries is dominant at temperatures above Tc. It is known that in order to reduce the resistance of today's PTC elements, it is important to control the bulk that governs the resistance at room temperature.

The room temperature resistivity of this PTC element is generally expressed as follows.

ρ (PTC) = ρ (bulk) = 1/n (D) ・e・μ (n (D) - donor density, e = orientation of electrons, μ = mobility) Therefore, the resistance of a single C element is , depends on the donor density, i.e., the degree of oxygen vacancies in the bulk, and the low resistance PT
In order to reduce Ci to 1!7, it is necessary to increase the concentration of m-element defects.

The concentration of M-cord defects is determined by semiconductor elements such as YlLa and Nb (
dopant) or 5in2, Al t.

There is a close correlation with the type of sintering aid (flux) and the amount added. Furthermore, as shown in FIG. 6, the present inventors have confirmed that for the same composition, the resistance changes greatly due to slow cooling and rapid cooling in the cooling process after firing.

The reason why the resistance decreases due to the rapid cooling in the cooling process after firing is that the oxygen defects (BaT 1o3-x) formed by the release of oxygen at high temperatures during the firing process are frozen in the cold IJ1 and inside the bulk. This is thought to be due to an increase in the oxygen defect concentration.

The present invention is based on this phenomenon.

That is, in the first invention, for example, as shown in the flowchart of FIG. 1, barium titanate calcined powder stirred by the calcining process is heated at a temperature of 1000 to 1250°C, and then heated at a temperature of 500°C/hour or more. Oxygen defects in this powder are eliminated by performing a heat treatment step of rapid cooling at a cooling rate of
The calcined powder containing high lIa oxygen defects is molded using a calcined powder containing high lIa oxygen defects, and the oxygen defects are confined in the bulk by firing in the atmosphere using a normal method. .

When the heating temperature is less than 1000°C, almost no effect is observed. This is presumed to be closely related to the temperature at which oxygen is released at high temperatures. or,
If the temperature exceeds 1250° C., a part of the raw material becomes a semiconductor, which causes an upper limit in resistance, which is not preferable.

Note that the atmosphere for the heat treatment is not limited to the air, but may also be a neutral atmosphere such as nitrogen or argon, or a reducing atmosphere such as a nitrogen atmosphere containing about 1100 ppm of hydrogen.

The heating time depends on the heating temperature, but is 0.5 hours or more.

The second invention is characterized in that in the steps from the calcination step to the calcination step, from the beating calcination to the calcination to convert it into a semiconductor, the calcination powder or molded body is heated in an oxygen-deficient atmosphere containing 5% by volume or less of oxygen, or in a neutral atmosphere. Alternatively, the material is heat treated in a reducing atmosphere at a temperature jσ of 800 to 1250° C., and then fired in the atmosphere by a normal method.

The second invention is to obtain barium titanate powder or a compact thereof with a high oxygen defect degree by heat-treating in an atmosphere lacking in oxygen or having no oxygen at all, and then firing the powder in the atmosphere by a normal method. A low-resistance PTC thermistor with a high oxygen defect concentration in the bulk can be manufactured at low cost without reducing grain boundaries.

If oxygen exceeds 5% by volume in the M-depleted atmosphere, the resistivity will normally be 50 cm or more, which is not preferable.

As the neutral atmosphere, an inert gas such as argon or helium, nitrogen, or the like can be used. As the reducing atmosphere, a reducing gas such as hydrogen may be used in the neutral atmosphere.

Regarding the heat treatment temperature, at a temperature lower than 800°C (for example, No. 2 in Table 2), the reduction of the barium titanate powder is not sufficient, and at a temperature exceeding 1250°C (for example, No. 2 in Table 2), the reduction of the barium titanate powder is insufficient. No. 9> is not preferable because the powder undergoes significant grain growth during heat treatment, resulting in an increase in specific resistance at room temperature.

The treatment time is preferably 1 hour or more. In addition, when the barium titanate powder or molded body is cooled to room temperature after the heat treatment and before firing, it is preferable to cool it in the above-mentioned oxygen-deficient or oxygen-free atmosphere. In this case, rapid cooling is not required. When cooling in air, the temperature is 500℃/
Requires rapid cooling to H or higher.

The composition of the barium titanate raw material powder used in the present invention is not limited to BaTiO3, but also includes Tc and R-T (
Resistance - m degrees) Characteristics wo a, II l! ! l t le tc
A similar effect can be achieved by adding elements such as Pb, Sr, Ca, and Mn.

[fruit[] The present invention will be explained below with reference to Examples.

(Example 1) In this example, as shown in FIG. Made porcelain. The raw material composition, sintered compact formation, heat treatment temperature, cooling rate, and treatment atmosphere were as shown in Test Nos. 2 to 23 in Table 1. Note that No. 1 is a conventional example that does not include a heat treatment process.

First, f3 a CO3 is 1.00 mol, Tilt is 1°02 mol, YzO3 is 080025 mol, and for a total of 1001 ffi parts of these champions, 5 ift is 0° 5 double aged part, AlO3 is 0.3 double positive part, and further, Mno2 0.0
After mixing 0.002 mol, water was added to a ball mill using agate boulders and mixed for 20 hours.

After drying, dry at 150°C for 24 hours, and then dry at 1100°C.
℃ for 4 hours to obtain 1 q of barium titanate calcined powder. Then, this calcined powder is heated for 1 hour at each temperature of 900 to 1300°C shown in Table 1 using a rotary kiln, and then rapidly cooled using the prescribed means and cooling rate shown in Table 1 to obtain a treated powder. I got it. The processing atmosphere in this case was as shown in Table 1. This treated powder is pulverized and molded using a normal method, and then heated to 1350°C in the atmosphere.
Firing was performed for 1 hour to obtain a fired body.

Next, the end face of each fired body is polished, Ni electroless plating and AQ paste M pole are applied, and the specific resistance (ρgo) is
and RT characteristics (ΔR) were evaluated, and the results are shown in Table 1. In addition, the relationship between cooling rate and specific resistance (No.
, 2 to No. 8) are shown in FIG. 2, and the RT characteristics of No. 1 (conventional example) and No. 8 (invention) are shown in FIG. 3. In addition, the criterion is that the specific resistance (ρ20) is 5Ω・cm
Hereinafter, RT characteristics (ΔR) of 2 digits or more were marked as O, and the rest were marked as X.

According to the results, conventional examples that do not have a treatment process (No. 1>), cooling rates of 200°C/hour or less (No. 2 to 4), and cases where the treatment 1M + temperature is 900°C ( N
o, 9.14), it is 1300℃ (No. 13
．． 18) Each of the conventional examples and comparative examples has a specific resistance of 5.
It was 0.01 or more. On the other hand, other test examples (the present invention)
Although the RT characteristics (ΔR) were slightly deteriorated, the specific resistances were all as small as 5Ω·CI or less compared to the conventional examples and comparative examples. That is, when the heat treatment humidity is 1000 to 1250°C and the cooling rate is 500°C/hour or more as shown in Figure 2, low resistance P
I was able to beat TC Suryo by 1. Especially the cold u1 thirst level is 10
In the case of air water cooling (No. 7) and submerged water cooling (No. 8.15 to 17) at 00°C/hour or more, the specific resistance is 0.9.
7 to 1.5 Ω・cm, which is extremely small.
If the processing temperature is 1200 to 1250℃ (No.
.

16.17) showed a value of 1Ω·C- or less, which was extremely good.

In addition, the composition of the raw material powder, ie, the sintered body phase or 8aTiOx
(7) also (1) (No, 5~8.10~12.15~1
Similar effects could be obtained not only with 7.21 to 23) but also with those containing Pb or Sr (No. 19.20).

(Example 2) Under the same conditions as No. 8 of the above-mentioned Example @1, Freon was used instead of water as the quenching solvent. As a result, ρ2o becomes 1.
A positive characteristic semiconductor porcelain with a value of 1Ω·CIa1Δ[< of 2.5 digits was tested.

(The following is a blank space) <Example 3> In this example, as shown in FIG.
Predetermined semiconductor porcelain was manufactured. The heat treatment conditions used were those shown in Test Nos. 32 to 53 in Table 2. Please note that No
, 31 are conventional examples that do not include this heat treatment step.

First, BaCO3, Ti1t, 5ift, At t03,
After combining raw materials such as Y2O2 and Mn0t to a predetermined Mal1,
Water was added to a ball mill using agate boulders and mixed for 20 hours. In addition, the same composition was used for each test example corresponding to each test example of Example 1. After that, it was dried at 150℃ for 24 hours, and further calcined at 1100℃ for 4 hours.
A calcined barium ditanate powder was obtained. This calcined powder is
The mixture was packed in a 2O2 pot, kept at a predetermined temperature shown in Table 2 for a predetermined time in a furnace having a predetermined atmosphere shown in Table 2, and then subjected to heat treatment in which it was slowly cooled in the mock furnace.

After that, pulverization was carried out for 20 hours using the ball mill described in L, and after drying, about 1 wt of polyvinyl alcohol was
% was added and granulation was performed. The granulated powder that has been pounded in this way is
After molding at a pressure of 00 kq/c+aZ, firing was performed in the atmosphere at 1350°C for 1 hour using a conventional method to obtain a disc-shaped fired body (20IiIllφ, thickness 2.511Im).

Furthermore, the end face of this fired body was polished, Nt electroless plating and 1 m of AQ paste were applied, and its specific resistance (ρ10
> and RT characteristics (ΔR) were evaluated, and the results are shown in Table 2.

Incidentally, the RT characteristics for No. 31 (conventional example) and No. 35 (invention) are shown in FIG.

According to this conclusion, there is a conventional example that does not have a heat treatment process (No. 31), a case where the temperature 1σ is 700°C (No. 32), and a case where it is 1300°C (No. 7) (N
o, 39), H1liaI'l 10% (7
) M passing away [ITl-like things (No. 46), each conventional example,
All of the comparative examples had specific resistances of 5Ω·ant or more. On the other hand, in other test examples (the present invention), the RT characteristics (
(ΔF), it was possible to obtain a PTC* element with low resistance and practical use, although it was slightly deteriorated. Especially [3aTi0
If the sintered body composition is No. 3, the atmosphere is neutral or reducing, and the processing temperature is 1000 to 1200°C, (No. 35
~37.41~45) showed a significantly small resistivity of 1.0 Ω·cm or less.

In addition, as in No. 21, the same effect can be obtained even if a molded body is used, and it will be effective if the same treatment is performed in any step from the first calcination to the semiconductor formation at the time of firing. is clear. In addition, the composition of the raw material powder, that is, the composition of the sintered body, is
3aTio3 (No, 33-38.40-48.
Similar beam effects could be obtained not only with 51 to 53) but also with those containing Pb or Sr (NO049, 50).

(The following is a blank space) [Effects of the Invention] The manufacturing method of the first invention mainly involves heating BaTiO3 powder at a predetermined temperature for a predetermined time and rapidly cooling it, thereby actively introducing oxygen defects that are formed at high temperatures. The sintered powder is used to cover a positive characteristic semiconductor (LA) device made of Ti. According to the present vJ manufacturing method, it is possible to reduce the specific resistance of this positive characteristic semiconductor porcelain.

The manufacturing method of the second invention includes heat-treating BaTiO3 powder and its molded body at a predetermined temperature for a predetermined time in an oxygen-deficient or aSS-free atmosphere, and then firing it in the atmosphere as a normal method. This increases only the M1g defect concentration in the bulk without reducing grain boundaries where PTC characteristics occur.

According to this manufacturing method, low resistance positive characteristic semiconductor ceramics can be manufactured at low cost.

[Brief explanation of the drawing]

FIG. 1 is a flowchart showing the manufacturing method of the first invention, FIG. 2 is a graph showing the relationship between cooling rate and specific resistance in Example 1, and FIG. 3 is a graph showing an example of the resistance-temperature characteristics of Example 1. , FIG. 4 is a flowchart showing the second invention and the conventional manufacturing method, FIG. 5 is a graph showing an example of resistance-temperature characteristics of Example 30, and FIG. 6 is a graph showing the general relationship between cooling rate and specific resistance. It is. Patent applicant Nippondenso Co., Ltd. Agent Patent attorney Hiroshi Okawa Figure 1 Temperature ('C) Figure 5 Temperature ff ('C); Week of dispute ff ('C/weak)

Claims (2)

[Claims] (1) A method for manufacturing positive characteristic semiconductor porcelain containing barium titanate as a main component, which includes a mixing step of mixing raw material powders, and calcining the mixed powder mixed in the mixing step to produce mainly barium titanate. A calcination step for synthesizing a calcined powder, and a barium titanate calcined powder milled by the above calcination step at a temperature of 1,000 to 12
A heat treatment step of heating in a temperature range of 50°C and then rapidly cooling at a cooling rate of 500°C/hour or more, and a molding process in which the treated barium titanate calcined powder is pulverized to form a molded body of a predetermined shape. 1. A method for manufacturing positive characteristic semiconductor porcelain, characterized in that a step and a firing step of firing the molded body in the atmosphere are sequentially carried out. (2) A method for manufacturing positive characteristic semiconductor porcelain containing barium titanate as a main component, which includes a mixing step of mixing raw material powders, and calcining the mixed powder mixed in the mixing step to produce mainly barium titanate. a calcination step for synthesizing a calcined powder; a molding step for pulverizing the calcined barium titanate powder to form a molded body of a predetermined shape; and a firing step for firing the molded body in the atmosphere. In the method of manufacturing a positive characteristic semiconductor, after the calcination step and before the calcination step, in one of a neutral atmosphere, a reducing atmosphere, and an oxygen-deficient atmosphere containing 5% by volume or less of oxygen, the 1. A method for producing positive characteristic semiconductor porcelain, which comprises performing a treatment step of heat-treating the calcined barium titanate powder or the molded body in a temperature range of 800 to 1250°C.