JPS61212001A - Low resistance ptcr thermistor and manufacture thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a new FTOR thermistor made of barium titanate semiconductor ceramic and a method for manufacturing the same. Resistivity below one point (switching temperature) is 0.10 (7
) The present invention relates to an ultra-low resistance PTO thermistor and its manufacturing method as follows.

(Prior art) Barium titanate semiconductor porcelain flPTOR having a positive temperature coefficient of resistance (hereinafter referred to as PTOfL) is used as a self-temperature control heating element, and conventionally such barium titanate semiconductor porcelain mainly contains RaCO3 and TiO7. Trace amounts of semiconducting elements I La and Sb are used as raw materials and particles.
It is manufactured by press-molding semiconductor powder obtained by solid-phase reaction of a mixed powder to which fluorine, Y, Nb, etc. are added, and then firing it. n7cPTO obtained by this method
R thermistors usually have a structure consisting of particles with abnormal grain growth, and the magnitude of the P T OR effect obtained (referred to as the ratio of increase in resistivity) is generally as small as about 2 to 4 orders of magnitude. In order to improve this FTOR effect, a trace amount of Mn'
It has been done to add an acceptor element such as p-Or, or to make norium titanate porous to have a particle size of about 2 to 5 μm (for example, in JP-A-56-1).
(Refer to No. 58401) The magnitude of the PTOR effect was improved by 6 to 7 orders of magnitude for the helmsman, and about 7 to 9 orders of magnitude for the latter.

On the other hand, the magnitude of the resistivity of barium titanate semiconductors below the Curie point is a very important issue in its application, as it relates to the switching function of the FTOR thermistor, the magnitude of the applied voltage, the magnitude of heat generation, etc. Therefore, attempts have been made to develop a low resistance PTOR thermistor having a resistivity of 0.10 or less at room temperature. However, the resistivity ρ of a material is expressed as ρ = (n e II ), where the conduction electron density is n%, the electron charge e, and the electron mobility. As long as a semiconductor is used, its resistivity at room temperature is equal to the resistivity inside the particle, and even the best one has n =
2 X 1018cm-3, e=1.6X10''''19
0, Fl, 0m-V-'1, ρ = 3Ω, and the resistivity at room temperature, that is, below the Curie point, is 0.1Ωd.
The following is impossible in principle, and in fact, there has been no successful example of manufacturing such a PTOR thermistor.

(Problems to be Solved) The present inventors completed the present invention as a result of conducting various studies to provide a low resistance PTOR thermistor that has a low resistivity of 0.1Ω or less at room temperature and has a large PTOR effect. That's what I came to do.

(Means for solving the problem) Low resistance PTC of the present invention! R, thermistor has a barium titanate surface layer or a fine particle layer interposed on the surface and grain boundaries of ceramic particles having metal conductivity,
Examples of intervening conditions include cases in which a barium titanate surface layer with a uniform thickness exists at the grain boundaries of metal-conductive ceramic particles, and gaps between metal-conductive ceramic particles (grain boundary thickness of approximately 1 μm).
(below), there are cases where fine particles of ha-13ium titanate are present.

To explain the drawings, as shown in Figure 3, in the conventional Norium titanate-based semiconductor ceramic, semiconducting Norium titanate particles are bonded together, and the surface of each particle becomes insulating Titanate at a temperature higher than its switching temperature. However, in the present invention, as shown in FIG. 1, the semiconductive particles of Norium titanate are replaced with a metal conductive substance, and the surface of each particle of the substance is is covered with an insulating barium titanate surface layer above the switching temperature;
As shown in FIG. 2, semiconducting barium titanate is interposed in the gaps between the metal conductive particles.

The metal conductive substance used in the present invention has high conductivity, such as lanthanum-doped strontium titanate (Lmxarl-
xTHO3), lead acid, hexalium (BaPb03), etc. Thus, in the thermistor having a composite structure as in the present invention, the nitride titanate in the grain boundary portion provides PTOR characteristics, and the metal conductive particles in the skeleton serve to lower the overall resistivity.

In addition, the method for manufacturing the low resistance PTOR thermistor of the present invention involves adding a semiconductor element to the surface of metal conductive particles.
After coating the TiOs ultrafine particles, the resulting particles are pressure-molded and sintered. This particle layer must be prevented from being absorbed by the metallic conductive particles by diffusion.
Usually, the hot press method or normal pressure sintering method is used under sintering conditions at 1300° C. or lower. Another method is to sinter the mixture at a temperature of usually 1,300 to 1,400°C, and during the cooling process, the B a T + 03 component is precipitated at the grain boundaries, resulting in an extremely thin surface of RaTi O5 on the grain surface. It forms a layer.

In the present invention, the currently known P
By using means for increasing the TOR effect in combination, it is possible to obtain a thermistor having a low resistance of 0.1Ω or less at room temperature and a large PTOR effect. That is, RaTiO
Adding an acceptor element to 3 or B a T i O
By adopting sintering conditions that make B porous, the intervening R
By making a TiOs porous, a thermistor with low resistance and a large P T OR effect is obtained. Next, the present invention will be explained with reference to examples.

Example 1 Lanthanum-doped strontium titanate (Lax8r1-x'["i03
=0.01 to 0.02) Adjust the particles so that the particle size is approximately 50 μm. Next, a semiconductor element is added to the surface of the metal conductive particles by applying microcapsule technology to coat them with B a T r Os fine particles of 0.01 μm or less, and the thus obtained particle powder is processed. It is pressed and sintered using the hot press method or pressureless sintering method.

During sintering, it is necessary to prevent the 8a TiO3 layer on the surface from being completely absorbed into the 5iTi03 layer by diffusion. In addition, by increasing the density of the press-formed body of the sintered ship as much as possible, the F1aTi034 on the surface
It becomes possible to proceed with the sintering reaction between the two.

Since Ra T + Os and S r T + Os are completely solid solution substances, a thermally stable sintered body can be obtained without separation or peeling between the two phases. This sintered body exhibits a microstructure as shown in FIG. In addition, the P T OR sintered body having the structure shown in [F]l is obtained by sintering the above-mentioned collared composition powder at a temperature of 1350°C or higher by an atmospheric pressure sintering method.
It can also be obtained by using a multi-stage cooling method in the subsequent cooling process or by performing heat treatment.

Note that good PTOR characteristics can be obtained by adding an appropriate amount of an acceptor element to the grain boundaries.

Example 2 LaxSrl-xT of about 50 pm as in Example 1
Particles exhibiting metallic conductivity such as iO2 or BaPbO3 are prepared, and semiconductive Ba' having a particle size of approximately 0.1 μm is added to the particles.
The ri03 powder is mixed so that the Ra T' i05 particles surround the metal conductive particles. The thus obtained mixed powder is press-molded and sintered. At this time, the sintering conditions were controlled in the same manner as in Example 1 so that the sintering reaction between B a T + Os particles mainly proceeded, and Ra'I'i0
3. Prevent the particles from being absorbed by the metal conductive particles. The RaTi036 particles between the metal conductive particles are sintered to become porous under sintering conditions such that the particles grow to about 0.3 μm during the sintering process.

The obtained sintered body had a collared structure as shown in Figure 2.

present.

(Function) Next, the PT, OR thermistor having the structure obtained by the present invention has a resistivity of less than one Curie point and less than 0.1 Ωd,
It will be explained that it shows a PTOFL effect of three orders of magnitude or more. In other words, the resistivity ρ of the material is the resistivity ρLm of the metal conductive particles)
and the resistivity ρ(s) of the grain boundary Ra T i 03, and the total resistance is represented by the series connection of the intragrain resistance and the grain boundary resistance, so it is as follows.

ρ; ρ Cm) + ρ is)・r(s)/γ
(m) where γ(m) is the particle size of the metal conductive particles, r C
s) is the thickness of the grain boundary layer. Therefore, ρ(m)=0.
010 prepared.

ρ(s) = 3ΩQ and r(m) = 50μm%r(s
) = 1 μm (thickness of 3 BaTiO3 particles), then ρ = 0.07Ω, and by increasing γ(m) f further, ρ can be lowered to about 0.050Ω.

In addition, when such a low-resistance element is directly inserted into a circuit (2), the voltage across the terminals of the element usually does not exceed 1μ due to the relationship with the load resistance value of the circuit, so the thickness When a voltage of 1 cm is applied to a PTOR thermistor of 1 cPJt, a voltage of approximately 50 V/car is applied to the grain boundaries, so there is no noticeable deterioration in the PTOR effect with this level of electric field. Therefore, the Ra'ri03 particles, which originally exhibit a PTOR effect of six orders of magnitude or more, exhibit a PTOR effect of three orders of magnitude or more, which is sufficiently large for practical use, under this level of electric field.

(Effects) As described above, the present invention can provide a low-resistance PTOFL thermistor with a resistivity of 0.1Ω or less, without reducing the PTOR effect.
Therefore, the PTOR thermistor can be inserted directly into the power supply line and can be fully utilized as a non-contact switch and as an overheating prevention element 7 for each fin'1 path.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the organizational structure of the low resistance P 1' OR thermistor of the present invention, and the second factor is the low resistance FTOR of the present invention.
FIG. 3 is an explanatory diagram of the organizational structure of another embodiment of the thermistor. FIG. 3 is an explanatory diagram of the organizational structure of a conventional BaTiO3-based PTOR thermistor. 1...Metal conductive ceramic particles, 2...Semiconductive barium titanate fine particles, 3...Extremely thin insulating barium titanate surface layer procedural amendment April 17, 1985

Claims (1)

[Claims] 1. A low-resistance PTOR thermistor characterized in that a barium titanate fine particle layer is interposed on the surface and grain boundaries of ceramic particles having metal conductivity.2. The surface of BaTiO_3 ultrafine particles added with semiconducting elements is coated, the resulting particles are pressure-molded and then sintered, or a mixture thereof is sintered, and during the cooling process, a metal conductive material is formed by diffusion precipitation. Extremely thin BaTiO_3 on the particle surface
Method for manufacturing a low resistance PTCR thermistor characterized by forming a surface area