JP3245953B2 - Semiconductor porcelain having negative resistance temperature characteristics and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor porcelain having a negative resistance temperature characteristic suitable for an overcurrent prevention element for preventing an overcurrent in a switching power supply or the like at the initial stage of power-on.

[0002]

2. Description of the Related Art In a switching power supply or the like, a semiconductor porcelain having a negative temperature characteristic (a negative temperature coefficient thermistor) whose resistance decreases as the temperature rises in order to prevent an overcurrent at power-on. ) Is used. This negative temperature coefficient thermistor has a high resistance at room temperature, so it suppresses overcurrent at the initial stage of power-on such as a switching power supply, and also self-heats to raise the temperature to a low resistance. It has the characteristic of decreasing, and is widely used for various applications as an overcurrent prevention element.

However, a conventional negative characteristic thermistor used for a switching power supply or the like has a B constant representing the relationship between temperature and resistance of 2000 to 4000 K, and thus is susceptible to the influence of the ambient temperature. There is a problem that the initial resistance fluctuates greatly and the rise characteristics vary. In particular, there is a problem that the rise is too slow at a low temperature of 0 ° C. or less.

[0004] In order to solve the above problems,
A negative temperature coefficient thermistor having such a characteristic that the B constant is small near normal temperature (−50 to 50 ° C.) and becomes larger at a higher temperature.

[0005] As described above, barium titanate (Ba) is an element that rapidly increases when the B constant exceeds the phase transition point.
A device in which 20 wt% of Li ₂ CO ₃ is added to TiO ₃ ) has been proposed (Japanese Patent Publication No. 48-6352).

However, since this device has a large specific resistance at 140 ° C. of 10 ⁵ Ω · cm or more, there is a problem that power consumption in a steady state is large.

The present invention solves the above-mentioned problems. The resistance is low, the power loss during energization can be suppressed, and the B constant is small at room temperature and large at high temperatures. An object of the present invention is to provide a semiconductor porcelain having resistance temperature characteristics.

[0008]

In order to achieve the above object, a semiconductor ceramic having a negative resistance temperature characteristic according to the present invention is represented by the following formula: (Ba ₁ -x Ca _x ) _m TiO ₃ , wherein x, m each, Ri near range of 0.05 ≦ x ≦ 0.40 0.99 ≦ m ≦ 1.05, the B constant at 0.99 ° C., Contact to 25 ° C.
The ratio to the B constant is 2 or more and at 25 ° C
Of the specific resistance at 150 ° C.
It is characterized by two or more .

That is, according to the barium titanate-based semiconductor porcelain having a negative resistance temperature characteristic of the present invention , the Ba site is replaced with Ca by 5 to 40 mol% and the Ba site /
By setting the Ti site (molar ratio) in the range of 0.99 to 1.05, the resistance is suppressed, and the B constant at a temperature equal to or higher than the phase transition point (for example, 120 ° C.) from cubic to tetragonal is obtained. , are largely Do so that than the constant B in the phase transition point or lower.

Also, the present invention has a negative resistance-temperature characteristic.
The method for manufacturing a semiconductor porcelain is represented by the formula: (Ba ₁ -x Ca _x ) _m TiO ₃ , where x and m are respectively 0.05 ≦ x ≦ 0.40 0.99 ≦ m ≦ 1.05 . The B constant at 150 ° C is
The ratio to the B constant is 2 or more and at 25 ° C
Of the specific resistance at 150 ° C.
Manufacture of semiconductor porcelain having a negative resistance temperature characteristic of 2 or more
The method of making, mixing ceramic raw materials, calcined,
For calcined powder containing at least Ba, Ca, and Ti
Binder is added and mixed, molded into a predetermined shape, and obtained.
Characterized by sintering the molded body in a reducing atmosphere
ing.

For example, Ba and Ca carbonates and Ti
Mixing ceramic materials such as oxides and calcining
At least the calcined powder containing Ba, Ca, and Ti
Is added, mixed and molded into a predetermined shape.
By sintering the molded body in a reducing atmosphere , x is represented by the formula: (Ba ₁ -x Ca _x ) _m TiO ₃ , where x and m are respectively 0.05 ≦ x ≦ 0.40 0.99 ≦ A semiconductor porcelain having a negative resistance temperature characteristic in the range of m ≦ 1.05 is manufactured.
Of the B constant at 150 ° C.
The ratio to the B constant at 25 ° C. is 2 or more, and
The specific resistance at 25 ° C is lower than the specific resistance at 150 ° C.
Has a negative resistance temperature characteristic such that the ratio of
Semiconductor porcelain can be manufactured.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The features of the present invention will be described below in more detail by showing embodiments of the present invention .

The raw materials BaCO ₃ , CaCO ₃ , La ₂
O ₃ , TiO ₂ , and SiO ₂ powders are weighed so as to have a composition represented by the following formula: (Ba _0.998-X Ca _X La _0.002 ) _m TiO ₃ +0.01 SiO ₂ . Then, each raw material powder is wet-mixed with water in a ball mill for 5 hours, dried and calcined at 1150 ° C. for 2 hours. Next, a binder was added to the obtained powder (calcined powder), wet-mixed with a ball mill for 5 hours, pulverized, filtered and dried, and then pressed into a disk having a diameter of 10 mm. % In a mixed atmosphere of hydrogen (H ₂ / N ₂ = 3 vol%)
C. for 2 hours.

Then, In-G is applied to both sides of the sintered disc.
The resistance-temperature characteristics of the sample on which a was applied to form an electrode were measured. Ca amount x = 0.20, molar ratio of Ba site and Ti site (Ba site / Ti site) m = 1.01
Fig. 1 shows the relationship between the specific resistance and the temperature of the sample (resistance-temperature characteristics).
Shown in

The resistance-temperature characteristic shown in FIG. 1 is approximately 500 when the B constant is equal to or less than the phase transition point from cubic to tetragonal (120 ° C.).
K, a barium titanate-based semiconductor having a resistance temperature characteristic such that the temperature becomes about 2000 K or more at a phase transition point (120 ° C.) or more, and a B constant is small at room temperature and large at a high temperature It can be seen that porcelain has been obtained.

Tables 1 and 2 show characteristics such as the B constant and the specific resistance at 25 ° C. and 150 ° C. when the value of the amount x of Ca and the value of the molar ratio m are changed.

[0017]

[Table 1]

[0018]

[Table 2]

In Tables 1 and 2, * is added to the sample number.
Those with a mark are comparative examples outside the scope of the present invention , and the others indicate examples of the present invention .

As shown in Tables 1 and 2, when the amount x of Ca is 0.
For the examples of the present invention in which the molar ratio m is in the range of 0.99 to 1.05, the temperature (150 ° C.) or more is higher than the phase transition point (120 ° C.).
(° C.) shows that the B constant increases. Also,
Even if the value of the molar ratio m is in the range of 0.99 to 1.05,
As shown in FIG. 2, in a sample in which the value of Ca amount x is less than 0.05 (for example, the sample of sample No. 17 having Ca amount x = 0.00 and molar ratio m = 1.01), as shown in FIG. After showing the temperature characteristics, a negative resistance-temperature characteristic is shown. For this reason, 25
Specific resistance ρ at ° C., ratio resistivity ρ at 0.99 ° C., i.e., the rate of change in resistance (ρ25 ℃ / ρ150
° C) is 2 or less, which poses a practical problem.

Therefore, the value of the amount x of Ca is 0.05 to
0.40, by the value of the molar ratio m is to adjust the composition to be in the range of 0.99 to 1.05, the B constant at 0.99 ° C., ratio B constant at 25 ℃ (B150 ℃ / B25 C.) of 2 or more, and a resistance change rate (ρ25 ° C./ρ150° C.) of 2 or more can provide a semiconductor ceramic having negative resistance temperature characteristics.

In the above embodiment, the barium titanate-based semiconductor porcelain containing a small amount of La at the Ba site has been described. However, the semiconductor porcelain having a negative resistance temperature characteristic according to the present invention does not particularly contain La. In this case, the same effect as in the above embodiment can be obtained, and in addition to La, a rare earth element such as Y as a semiconducting agent and other trace components can coexist.

[0023]

As described above, the semiconductor porcelain having the negative resistance-temperature characteristic of the present invention has the following formula: (Ba _{1 -X} Ca _X ) _m T
represented by iO ₃ , wherein x and m are respectively 0.05 ≦ x ≦
In the range of 0.40,0.99 ≦ m ≦ 1.05, or
B constant at 150 ° C, B constant at 25 ° C
Is greater than or equal to 2 and the specific resistance at 25 ° C.
Of the specific resistance at 150 ° C. is 2 or more, so that the B constant at a temperature equal to or higher than the phase transition point from cubic to tetragonal (for example, 120 ° C.) Considerably larger than the B constant at temperatures below the transition point,
A semiconductor porcelain having excellent temperature stability at low temperatures and having a negative resistance-temperature characteristic having a large resistance reduction rate at high temperatures can be obtained. The semiconductor porcelain having the negative resistance temperature characteristic of the present invention is, for example, a Ba and Ca charcoal.
Mixing ceramic raw materials such as acid salts and oxides of Ti
Contains at least Ba, Ca, and Ti
Add the binder to the calcined powder and mix to form
Molding and sintering the resulting compact in a reducing atmosphere
Can be obtained by

[Brief description of the drawings]

FIG. 1 is a diagram showing a resistance temperature characteristic of a semiconductor ceramic having a negative resistance temperature characteristic according to an embodiment of the present invention .

FIG. 2 is a diagram showing a resistance temperature characteristic of a semiconductor ceramic having a negative resistance temperature characteristic of a comparative example.

────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yasunobu Yoneda 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto Murata Manufacturing Co., Ltd. (56) References JP-A-47-33294 (JP, A) JP-A Sho 57-64902 (JP, A) JP-A-54-44797 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01C ^7/ 02-7/22

Claims (2)

(57) [Claims] 1. The formula: (Ba ₁ -x Ca _x ) _m TiO ₃ , wherein x and m are each in the range of 0.05 ≦ x ≦ 0.40 0.99 ≦ m ≦ 1.05. Of the B constant at 150 ° C. to the B constant at 25 ° C.
The specific resistance at 25 ° C is higher than the specific resistance at 150 ° C.
Semiconductor ceramics having negative resistance-temperature characteristics, wherein the ratio is 2 or more . 2. The formula: (Ba _1-X Ca _X ) _m TiO _Three Where x and m are 0.05 ≦ x ≦ 0.40 0.99 ≦ m ≦ 1.05 And the B constant at 150 ° C is 25 ° C.
The ratio to the B constant is 2 or more and at 25 ° C
Of the specific resistance at 150 ° C.
Manufacture of semiconductor porcelain having a negative resistance temperature characteristic of 2 or more
Manufacturing method, Ceramic materials were mixed and calcined, at least Ba,
Add binder to calcined powder containing Ca and Ti
Add, mix and mold into a predetermined shape, It is characterized by sintering the obtained molded body in a reducing atmosphere.
Of manufacturing semiconductor porcelain having a negative resistance temperature characteristic.