TWI441203B - Positive thermal resistance element - Google Patents

Description

Positive thermal resistor component

The present invention relates to a positive thermal resistor component, particularly a positive thermal resistor component for motor applications.

The barium titanate (BaTiO ₃ )-based semiconductor ceramic has the following PTC (Positive Temperature Coefficient) characteristic: heat generation by application of a voltage, if the Curie temperature exceeds the Curie temperature from the tetragonal phase to the cubic phase (Curie temperature) ) The resistance value increases sharply. With this PTC characteristic, the semiconductor ceramic can be widely used for heating applications, motor starting applications, and the like.

However, for example, when a positive thermistor element is used for a motor application, in addition to the voltage used, an electromotive force generated by electromagnetic induction is applied when the motor is started, in particular, it is required to be resistant to an instantaneous high voltage ( Pressure resistance). Further, as a positive thermal resistor element which can obtain a high pressure resistance, for example, Patent Document 1 discloses that an inner region and an outer region are provided, and the porosity of the outer region is set to be larger than the positive thermal resistance of the inner region. Component.

[Advanced technical literature] [Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 9-17606

However, it is used in the positive thermal resistor element described in Patent Document 1. The semiconductor ceramic contains lead. Since lead is an environmentally-charged substance, it is required to develop a non-lead-based semiconductor ceramic that does not substantially contain lead in consideration of the environment.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a positive thermal resistor element which does not contain an environmentally-charged substance as a main component of a semiconductor ceramic and which is excellent in pressure resistance.

The positive thermistor element of the present invention is characterized in that it comprises a semiconductor ceramic containing BaTiO ₃ (wherein a part of Ba may be replaced by at least one of Ca, Sr, and a rare earth element) as a main component, And a pair of electrodes formed on the two main surfaces of the semiconductor ceramic; and the semiconductor ceramic has a pair of outer regions respectively connected to the pair of electrodes, and an inner region sandwiched by the pair of outer regions, The pore content ratio of the outer region is larger than the pore content of the inner region.

Further, in the positive thermistor element of the present invention, the above-mentioned main component is a general formula (Ba _1-xyz Ca _x Sr _y Ln _z )TiO ₃ (wherein Ln is a rare earth element, and the above x, y, z Compounds satisfying the conditions of 0≦x≦0.20, 0≦y≦0.20, 0.0035≦z≦0.0085).

Further, in the positive thermal resistance device of the present invention, it is preferable that the outer region has a void content of 12.5% or more and 25.0% or less, and a difference in void content between the outer region and the inner region is 5% or more.

Further, in the positive thermistor device of the present invention, it is preferable that the specific resistance of the outer region is higher than the specific resistance of the inner region, and the specific resistance of the outer region is represented as high ρ, and the specific resistance of the inner region is expressed as When ρ is low, the specific resistance ratio (high ρ-low ρ)/low ρ of high ρ and low ρ is expressed as Rρ, which satisfies 0.05≦Rρ≦0.50, and the total thickness of a pair of outer regions is represented as t ₁ . The thickness of the inner region is expressed as t ₂ , and the ratio t ₁ /(t ₁ +t ₂ ) of the thickness of the outer region to the thickness of the whole is expressed as Rt ₁ , which satisfies -0.8889 × Rρ + 49.444 ≦ Rt ₁ ≦ - 0.8889 ×Rρ+89.444.

According to the invention, it is possible to provide a positive thermistor element excellent in pressure resistance.

Hereinafter, embodiments for carrying out the invention will be described.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view showing a positive thermistor element of the present invention. The positive thermistor element 1 includes a semiconductor ceramic 11, and electrodes 12, 13. The semiconductor ceramic 11 contains BaTiO ₃ (wherein a part of Ba may be replaced by at least one of Ca, Sr, and a rare earth element) as a main component. Further, the semiconductor ceramic 11 does not substantially contain lead. Here, "substantially does not contain lead" means that lead is not contained in the main component. Therefore, it is not excluded that lead is inevitably mixed in a range of 10 ppm by weight or less in a range which does not affect the characteristics. Further, in the present specification, a material containing a lead component in the main component is referred to as a lead-based material.

The semiconductor ceramic 11 is formed in a plate shape having a main surface. In the present embodiment, the semiconductor ceramic 11 is formed in a disk shape, but may be formed in a rectangular parallelepiped shape.

The electrodes 12, 13 are formed on the two main surfaces of the semiconductor ceramic 11. Examples of the material of the electrodes 12 and 13 include Cu, Ni, Al, Cr, and Ni-Cr alloy. Further, in the present embodiment, the electrodes 12 and 13 have a one-layer structure. However, it can also be a multi-layer construction.

The semiconductor ceramic 11 has outer regions 15, 16 and an inner region 14. The outer regions 15, 16 are present on the main surface side of the semiconductor ceramic 11, and are connected to the electrodes 12, 13, respectively. Further, the inner region 14 is present inside the semiconductor ceramic 11, and is sandwiched by the outer regions 15, 16.

The present invention is characterized in that the porosity of the outer regions 15, 16 is greater than the porosity of the inner region 14. In this case, the resistance value (specific resistance value) of the outer regions 15 and 16 becomes larger than the resistance value (specific resistance value) of the inner region 14.

When a transient high voltage is applied to the semiconductor ceramic, the process for achieving the damage is as follows. When a voltage is applied to a normal semiconductor ceramic, the inside of the semiconductor ceramic is less likely to dissipate heat than the surface side, so the inside becomes a high temperature. Further, the inner side thermally expands to generate stress, and if the stress becomes excessively large, the semiconductor ceramic is broken. As described in the present invention, if the resistance of the outer regions 15, 16 is greater than the resistance of the inner region 14, the outer regions 15, 16 tend to be at a high temperature, and the stress generated by the thermal expansion of the inner region 14 is alleviated, so that the semiconductor ceramic 11 is Increased pressure resistance.

In the so-called flash withstand voltage test in which a high voltage is applied to the semiconductor ceramic and the pressure resistance is measured, there are two types of "breaking mode" and "longitudinal splitting mode" in the failure mode of the semiconductor ceramic. 2 and 3 are photographs showing the appearance of the semiconductor ceramic destroyed in the flash withstand voltage test. Fig. 2 is an example of a spallation mode, and Fig. 3 is an example of a longitudinal split mode. In the spallation mode of Figure 2, the fracture surface is smooth and the direction of failure is along the major surface of the semiconducting ceramic. On the other hand, in the longitudinal split mode of Figure 3, there is a concave surface on the fracture surface. The direction of the convexity is in the direction of the thickness direction of the ceramic.

The positive thermistor element of the present invention can have a fail safe function by studying the construction of the device for assembling the component. Here, the fail-safe function is a function in which the semiconductor ceramic is separated on the fracture surface and the circuit is cut off to protect the entire circuit when the semiconductor ceramic is broken by applying a high voltage.

However, when the semiconductor ceramic is broken in the spallation mode, the area of the fracture surface is larger than that of the longitudinal fracture mode, so that the fracture elements are easily brought into contact with each other, and the semiconductor ceramic is easily short-circuited after the destruction. Therefore, the spallation mode is not good.

Compared with the lead-based material, the BaTiO ₃ ceramics have low pressure resistance, and the failure mode in the flash withstand voltage test in the one-layer structure is the spallation mode. However, as described in the present invention, when the semiconductor ceramic is a three-layer structure having two outer regions and an inner region, the failure mode in the flash withstand voltage test is a longitudinal split mode. This mode is a failure mode unique to BaTiO ₃ ceramics, and even when a three-layer structure is formed in the lead-based material, the fracture mode is broken. Therefore, by forming the constitution of the present invention, it is possible to suppress the destruction of the spallation mode at the flash withstand voltage test.

Further, the main component of the semiconductor ceramic is preferably a general formula (Ba _1-xyz Ca _x Sr _y Ln _z )TiO ₃ (wherein Ln is a rare earth element, and the above x, y, and z satisfy 0 ≦ x ≦ 0.20, 0 ≦ The compound represented by y ≦ 0.20, 0.0035 ≦ z ≦ 0.0085). In this case, the effect of improving the pressure resistance is remarkable. Further, the molar ratio of (Ba, Ca, Sr, Ln)/Ti is not particularly limited, but is preferably in the range of 0.980 to 1.005. Further, in the semiconductor ceramic, in addition to the main component, Mn, Mg, Si or the like may be contained as an accessory component.

The semiconductor ceramic can be produced, for example, by press molding or sheet molding. At this time, the resin particles are contained in each slurry, and the amount of the resin particles contained in the portion corresponding to the outer region and the amount of the resin particles contained in the portion corresponding to the inner region are controlled, whereby the outer region and The porosity content of the inner region changes. Further, the content of the resin particles is changed here, for example, by adjusting the amount of the binder to be contained.

The pore content ratio was observed and measured by a microscope using a microscope.

Further, it is preferable that the void content of the outer region is 12.5% or more and 25.0% or less, and the difference in the void content ratio between the outer region and the inner region is 5% or more. In this case, there is an effect of a shorter recovery time. The recovery time is the time after a certain voltage is applied to the positive thermistor element for a certain period of time, and after the discharge is resumed until the resistance value is 2 times (2 times the resistance value at 25 ° C), the recovery time is shorter. The more suitable it is for motor use.

The upper limit of the difference in the void content ratio between the outer region and the inner region is not particularly limited, and is preferably 20.0% or less in consideration of the strength of the semiconductor ceramic.

Further preferably, the specific resistance of the outer region is higher than the specific resistance of the inner region, and the specific resistance of the outer region is represented as high ρ, and the specific resistance of the inner region is represented as low ρ, and the ratio of high ρ to low ρ When the resistance ratio (high ρ-low ρ)/low ρ is expressed as Rρ, 0.05≦Rρ≦0.50 is satisfied, and the total thickness of the pair of outer regions is represented as t ₁ , and the thickness of the inner region is represented as t ₂ . When the ratio of the thickness of the outer region to the thickness of the whole body t ₁ /(t ₁ +t ₂ ) is expressed as Rt ₁ , -0.8889 × Rρ + 49.444 ≦ Rt ₁ ≦ - 0.8889 × Rρ + 89.444 is satisfied. In this case, an excellent pressure increase rate can be obtained.

Next, a method of manufacturing the positive thermistor element will be described.

First, a raw material powder of a semiconductor ceramic is produced. First, a compound powder containing an oxide or a carbonate of a constituent element of a main component is mixed and calcined in a specific ratio to obtain a raw material powder of a main component. This method is generally called a solid phase synthesis method, and as another method, a wet synthesis method such as a hydrothermal synthesis method or an oxalic acid method can also be used.

In the raw material powder of the main component, Mn or Si, a vinyl acetate-based organic binder, and pure water, which are subcomponents, are added as needed, and are mixed with the medium in a wet manner to obtain the obtained powder. The slurry is dried to obtain a raw material powder of a semiconductor ceramic.

Then, after the raw material powder of the semiconductor ceramic is mixed with the resin particles, the formed body is obtained by press molding or full-sheet forming.

Then, the molded body is burned at 500 to 600 ° C in an atmosphere, a nitrogen atmosphere, or a mixed gas stream. Thereafter, it is calcined in the atmosphere at a temperature at which the semiconductor ceramic is semiconductorized, for example, 1250 to 1450 ° C, to obtain a semiconductor ceramic.

Then, electrodes are formed on the two main surfaces of the semiconductor ceramic. The electrode is formed by plating, sputtering, or baking. A positive thermistor element is fabricated in the manner described above.

Furthermore, the present invention is not limited to the above embodiments. For example, an alkali metal, a transition metal, Cl, S, P, Hf or the like may be contained in the semiconductor ceramic in an amount that does not impair the effects of the present invention.

Next, a test example to be carried out will be described based on the present invention.

[Test Example 1]

In Test Example 1, the flash withstand voltage test of the positive thermistor element was carried out and compared with the lead-based material.

(A) Production of raw material powder for semiconductor ceramics

First, each of BaCO ₃ , CaCO ₃ , SrCO ₃ , and Er ₂ O ₃ as a starting material of the main component was prepared. Further, each starting material was weighed and blended. Then, ethanol and a polymeric dispersant were added, and wet pulverization was carried out in a ball mill together with a PSZ (partially stabilized zirconia) ball for a certain period of time. Thereafter, the ethanol was dried, and granulated by a sieve having a mesh of 300 μm. Then, heat treatment was carried out for 2 hours in a temperature range of 800 to 1000 ° C to obtain a raw material powder of a main component.

Then, MnO and SiO ₂ which are starting materials of the subcomponent are prepared and added to the raw material powder of the main component. Then, a vinyl acetate-based organic binder was added, and wet pulverization was carried out in a ball mill together with the PSZ ball for a certain period of time. Then, after the slurry was dried, it was sized by a sieve having a mesh size of 300 μm to obtain a raw material powder of the semiconductor ceramic represented by the formula (1). In addition, the ratio of preparation of each sample number is shown in the following Table 1.

Composition (1): 100(Ba _1-xyz Ca _x Sr _y Ln _z )TiO ₃ +aMn+bSi

(B) Production of formed body

First, a first powder in which the raw material powder described above is 100% by weight, and a resin of a polymethyl methacrylate having a spherical shape and an average particle diameter of 20 μm are mixed with respect to 100% by weight of the above-mentioned raw material powder. A second powder of 4% by weight of particles.

Then, a molded body having a different void content ratio in the outer region and the inner region is produced. First, 1 g of the second powder was filled in the mold of the dry press, and pressurized at a pressure of 400 kgf/cm ² to form a portion corresponding to the outer region. Then, the first powder 1g was filled in a portion corresponding to the outer region, and pressurized at a pressure of 400 kgf/cm ² to form a portion corresponding to the inner region. Then, the second powder 1g is filled in a portion corresponding to the inner region, and pressurized at a pressure of 2000 kgf/cm ² to form a region corresponding to the outer region, and the entire compression is performed, thereby forming a three-layer structure. Shaped body.

Moreover, for comparison, 3 g of the first powder was filled and pressurized at a pressure of 2000 kgf/cm ² to prepare a molded body having a single-layer structure.

(C) Fabrication of positive thermal resistor components

Then, the obtained molded body was calcined at 1,350 ° C to obtain a semiconductor ceramic having a diameter of 16 mm and a thickness of 2.5 mm. At this time, since the resin particles contained in the second powder disappear and the portion of the resin particles becomes a void, the void content ratio in the outer region is larger than the void content in the inner region. The cross section of the polished element was observed with a microscope and the void content was measured. As a result, in the present test example, the void content of the outer region was 20%. On the other hand, the void content of the inner region was 5%.

Then, a conductive paste containing Ni and Ag as a main component is applied onto both main surfaces of the semiconductor ceramic and baked to form an electrode.

The positive thermistor elements of sample Nos. 1 to 19 were produced as described above. Further, for comparison, a positive thermal resistor element containing sample numbers 20 to 22 of Pb was also produced.

(D) Characteristic evaluation

First, the positive thermal resistance element of the 1-layer structure is determined by the laser flash method. The thermal conductivity of the sample.

Then, a flash withstand voltage test was carried out. First, the resistance value of each sample at room temperature (25 ° C) was measured by a four-terminal method. Then, after applying a voltage of 100 V for 3 seconds to each sample, the temperature was lowered to room temperature and the resistance value was measured again. Further, when the measured resistance value does not change from the initial resistance value, the voltage is increased and the same measurement is repeated. Further, the voltage value before the semiconductor ceramic is broken and the resistance value is changed is set as the withstand voltage value. In addition, when the withstand voltage value in the one-layer structure is 100%, the rate of increase in the withstand voltage value in the three-layer structure at this time is taken as the withstand voltage increase rate. The results are shown in Table 1. Further, a sample having a * in the sample number is outside the range of the present invention.

According to Table 1, as in sample Nos. 1 to 19, in the general formula (Ba _1-xyz Ca _x Sr _y Ln _z )TiO ₃ (wherein Ln is a rare earth element, the above x, y, and z satisfy 0≦x≦) Within the range of the composition represented by 0.20, 0≦y≦0.20, 0.0035≦z≦0.0085, the pressure increase rate is 50% or more. This value is a larger value than 40 to 43% of the sample number 20 to 22 containing lead. Further, the failure mode in the flash withstand voltage test was a longitudinal split mode in sample numbers 1 to 19, and a spallation mode in sample numbers 20 to 22.

[Test Example 2]

In Test Example 2, the relationship between the void content ratio of the outer region and the inner region and the recovery time was evaluated. The manufacturing method of the positive thermistor element was the same as that of the test example 1, and the composition of the semiconductor ceramic was the same as that of the sample No. 4 of the test example 1. Further, the amount of PMMA mixed in the raw material powder of the semiconductor ceramic is changed, whereby the positive thermal resistor elements of the sample numbers 31 to 40 having different void contents in the inner region and the outer region are produced. The recovery time was measured after the voltage of 150 V was applied for 10 minutes, and the time until the resistance value returned to the value of 2 times was measured after the discharge.

The results of the void content, specific resistance, and recovery time of sample numbers 31 to 40 are shown in Table 2.

In sample No. 31, the porosity of the outer region was as low as 10.0%, and the recovery time was as long as 52 seconds. Further, in sample No. 32, the difference in the void content ratio between the outer region and the inner region was as small as 2.5%, and the recovery time was as long as 50 seconds. On the other hand, in sample numbers 33 to 40 in which the outer region is 12.5% or more and the difference in void content between the outer region and the inner region is 5% or more, the recovery time is within 46 seconds, and the recovery time is small. result.

[Test Example 3]

In Test Example 3, the ratio of the specific resistance ratio of the specific resistance of the outer region to the inner region and the ratio of the thickness of the outer region of the element to the thickness of the entire element were changed using the semiconductor ceramic of the same composition. Positive thermal resistance device (sample No. 41~59).

Further, in order to compare with the positive thermistor elements of sample numbers 41 to 59, a positive thermal resistor element for comparison using the low-p material of each of sample numbers 41 to 59 and having a one-layer structure was prepared.

The manufacturing method of the positive thermistor element was the same as that of the test example 1, and the same as the sample No. 4 of the test example 1 was used for the composition of the semiconductor ceramic.

The specific resistance ratio of the specific resistance of the outer region to the specific resistance of the inner region is changed by changing the amount of resin particles contained in the outer region and changing the void content of the outer region and the inner region. Further, as described above, since the specific resistance of the outer region is higher than the specific resistance of the inner region, the specific resistance of the outer region is referred to as "high ρ", and the specific resistance of the inner region is referred to as "low ρ". Further, the ratio of the high ρ to the low ρ (high ρ-low ρ)/low ρ is denoted as Rρ.

The ratio of the thickness of the outer region of the component to the thickness of the entire component is varied by varying the thickness of the outer region and the thickness of the inner region. Further, the total thickness of the pair of outer regions is referred to as "t ₁ ", the thickness of the inner region is referred to as "t ₂ ", and the ratio of the thickness of the outer region to the thickness of the whole is t ₁ /(t ₁ +t ₂ ) is marked as "Rt ₁ ".

Table 3 shows: the ratio of the high ρ to the low ρ of each positive thermistor of sample Nos. 41 to 59, the resistance ratio Rρ [(high ρ - low ρ) / low ρ], and the thickness of the outer region of the component The ratio Rt ₁ [t ₁ /(t ₁ +t ₂ )] of the thickness of the entire element. Further, in Table 3, the withstand voltage (three-layer structure withstand voltage) [V] of each positive thermistor of sample Nos. 41 to 59 is used to compare the resistance of the positive thermistor of the positive thermistor element. The pressure (one-layer structure withstand voltage) [V] and the pressure increase rate [%] of the increase rate of the withstand voltage value of the three-layer structure when the withstand voltage value of the one-layer structure is 100%. In the column of the pressure increase rate, "◎" indicates that the pressure increase rate is 50% or more, and "○" indicates that the pressure increase rate is less than 50%.

Further, Fig. 4 shows the ratio Rt ₁ of the specific resistance ratio Rρ of the high ρ and the low ρ of the positive thermal resistor elements of the sample numbers 41 to 59 and the thickness of the outer region as a whole. In FIG. 4, the number indicates the sample number, and "◎" indicates that the pressure increase rate is 50% or more, and "○" indicates that the pressure increase rate is less than 50%.

As can be seen from Fig. 4, the specific resistance ratio Rρ[(high ρ-low ρ)/low ρ] of the high ρ and the low ρ satisfies 0.05 ≦Rρ ≦ 0.50, and the ratio of the thickness of the outer region t _{1 to} the thickness of the entire element Rt _{When 1} [t ₁ /(t ₁ +t ₂ )] satisfies -0.8889 × Rρ + 49.444 ≦ Rt ₁ ≦ - 0.8889 × Rρ + 89.444, the withstand voltage increase rate is 50% or more, and is preferable.

[Test Example 4]

In Test Example 4, the specific resistance ratio Rρ [(high ρ - low ρ) / low ρ] of the high ρ and the low ρ was maintained at 45% by various changes in the composition of the semiconductor ceramic to be used, and The ratio Rt ₁ [t ₁ /(t ₁ +t ₂ )] of the thickness of the outer region t _{1 to} the thickness of the entire element is maintained at 25%, and seven kinds of positive thermistor elements having different withstand voltages are produced (sample No. 61~66).

Further, in order to compare with the positive thermal resistors of sample Nos. 61 to 66, a positive thermal resistor for comparison using the low-ρ materials of the samples 61 to 66 and having a one-layer structure was prepared.

Table 4 shows: the ratio of the high ρ to the low ρ of the positive thermal resistors of the sample numbers 61 to 66, the resistance ratio Rρ [(high ρ - low ρ) / low ρ], and the thickness of the outer region of the component occupies the component The ratio of the thickness of the whole is Rt ₁ [t ₁ /(t ₁ +t ₂ )]. Further, in Table 4, the withstand voltage (three-layer structure withstand voltage) [V] of each positive thermistor of sample Nos. 61 to 66, and the positive thermal resistor of the positive thermal resistor element for comparison are shown. The withstand voltage (one-layer structure withstand voltage) [V] and the pressure increase rate [%] of the increase rate of the withstand voltage value of the three-layer structure when the withstand voltage value of the one-layer structure is 100%. In the column of the pressure increase rate, "◎" indicates that the pressure increase rate is 50% or more, and "○" indicates that the pressure increase rate is less than 50%.

As shown in Table 4, in the range of 0.05 ≦Rρ≦0.50, and -0.8889×Rρ+49.444≦Rt ₁ ≦-0.8889×Rρ+89.444, even if Rρ and Rt _{1 are} maintained at a certain level, even if used Various changes in the composition of the semiconductor ceramics can also achieve a higher withstand voltage increase rate of 50% or more.

1‧‧‧ Positive thermal resistor components

11‧‧‧Semiconductor Ceramics

12, 13‧‧‧ electrodes

14‧‧‧Inside area

15, 16‧‧‧ outside area

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional view showing a positive thermistor element of the present invention.

Fig. 2 is an example of an appearance photograph of a semiconductor ceramic which is destroyed in a withstand voltage test and is a layer splitting mode.

Fig. 3 is a photograph showing the appearance of a semiconductor ceramic which is destroyed in a withstand voltage test, and an example of a longitudinal split mode.

4 is a graph showing the ratio Rt ₁ of the thickness of the outer region of the sample Nos. 41 to 59 in the test example 3 to the thickness of the whole, and the specific resistance ratio Rρ of the high ρ and the low ρ.

1‧‧‧ Positive thermal resistor components

11‧‧‧Semiconductor Ceramics

12, 13‧‧‧ electrodes

14‧‧‧Inside area

15, 16‧‧‧ outside area

Claims (4)

A positive thermistor element, characterized in that it comprises a semiconductor ceramic containing BaTiO ₃ (wherein a part of Ba may be replaced by at least one of Ca, Sr, and a rare earth element) as a main component, and And forming the pair of electrodes on the two main surfaces of the semiconductor ceramic; and the semiconductor ceramic has a pair of outer regions respectively connected to the pair of electrodes and an inner region sandwiched by the pair of outer regions, The void content of the outer region is larger than the void content of the inner region, wherein the outer region has a void content of 12.5% or more and 25.0% or less, and the difference between the outer region and the inner region has a void content of 5% or more. The positive thermistor element of claim 1, wherein the main component is of the formula (Ba _1-xyz Ca _x Sr _y Ln _z )TiO ₃ (wherein Ln is a rare earth element, and the above x, y, and z satisfy 0 ≦) The compound represented by x ≦ 0.20, 0 ≦ y ≦ 0.20, 0.0035 ≦ z ≦ 0.0085). The positive thermistor element of claim 2, wherein the outer region has a void content of 12.5% or more and 25.0% or less, and a difference in void content between the outer region and the inner region is 5% or more. The positive thermistor element according to any one of claims 1 to 3, wherein a specific resistance of the outer region is higher than a specific resistance of the inner region, and the specific resistance of the outer region is represented as a high ρ, the inner region The specific resistance is expressed as low ρ, and when the specific resistance ratio (high ρ-low ρ)/low ρ of high ρ and low ρ is expressed as Rρ, 0.05≦Rρ≦0.50 is satisfied, and the total of the pair of outer regions is The thickness is expressed as t ₁ , the thickness of the inner region is represented as t ₂ , and the ratio t ₁ /(t ₁ +t ₂ ) of the thickness of the outer region to the thickness of the whole is expressed as Rt ₁ , which satisfies -0.8889×Rρ+ 49.444≦Rt ₁ ≦-0.8889×Rρ+89.444.