TWI881805B - Positive temperature coefficient thermistor and its manufacturing method - Google Patents

Abstract

The present invention provides a positive temperature coefficient thermistor, which has the characteristics of high withstand voltage and low room temperature resistance by adjusting the contact ratio between particles contained in its ceramic sintered body. The present invention also provides a ceramic composition, a ceramic sintered body and a method for manufacturing a positive temperature coefficient thermistor, so as to obtain a positive temperature coefficient thermistor with high withstand voltage and low room temperature resistance.

Description

Positive temperature coefficient thermistor and its manufacturing method

The present invention relates to a positive temperature coefficient thermistor. The present invention also relates to a ceramic composition, a ceramic sintered body formed by sintering the ceramic sintered body, and a method for manufacturing a positive temperature coefficient thermistor including the ceramic sintered body.

Positive temperature coefficient thermistor (PTC thermistor) is a variable resistor whose resistance value will increase as the temperature of the resistor body increases. Therefore, it can be used as a heating element, a switching element, and a sensing element.

Household appliances or consumer electronic products used at room temperature rely heavily on PTC thermistors to achieve constant temperature heating, motor starting, overheat protection, and overcurrent protection. With the trend of high performance of electronic equipment, it is necessary to develop products that can cope with high voltages, so the higher the withstand voltage strength of PTC thermistors, the better. Therefore, thermistors with both low room temperature resistance and high withstand voltage strength are urgently needed to meet market demand.

To meet the above needs, the present invention provides a positive temperature coefficient thermistor, comprising: a ceramic body and two external electrodes, wherein the two external electrodes are respectively arranged on opposite sides of the ceramic body; the ceramic body comprises a ceramic sintered body and an internal electrode overlapping each other; the ceramic sintered body has a plurality of particles and a plurality of pores, and the composition of the ceramic sintered body comprises barium titanate; and the contact rate of the plurality of particles is 20% to 37.5%; wherein the contact rate is observed by a scanning electron microscope A cross section of the temperature coefficient thermistor is circled to select an area. In the area, the sum of the perimeters of the plurality of particles (Lt), the sum of the perimeters of the plurality of holes (Lp), and the perimeter of the area (La) are measured. The total contact length (Lc) of the plurality of particles is first obtained according to Formula I, and then the contact rate is obtained according to Formula II: Lc=(Lt-Lp-La)/2 (Formula I); and contact rate (%)=Lc/(Lc+Lp)×100 (Formula II).

According to the present invention, by adjusting the contact rate between the plurality of particles in the ceramic sintered body, the positive temperature coefficient thermistor can have the characteristics of high withstand voltage and low room temperature resistance.

According to the present invention, the sum of the perimeters of the plurality of particles (Lt) will include the "overlapping perimeters" and "non-overlapping perimeters" of the plurality of particles, so when calculating the total contact length (Lc) of the plurality of particles, the "non-overlapping perimeters", that is, the sum of the perimeters of the plurality of holes (Lp) and the perimeter of the region (La) must be deducted. In addition, the "overlapping perimeters" include the perimeters of "two overlapping single sides", and the length of the contact point is repeatedly calculated, so it is necessary to divide by 2 to obtain the total contact length (Lc) of the plurality of particles.

According to the present invention, the contact rate is calculated by calculating the ratio of the length of the overlapping of the plurality of particles in the "inside" of the region, so the denominator of Formula II does not include the perimeter (La) of the region.

In one embodiment, the withstand voltage of the positive temperature coefficient thermistor is greater than 20 volts (V) and less than 100 volts, for example: 21 volts, 22 volts, 23 volts, 24 volts, 25 volts, 30 volts, 40 volts, 50 volts, 60 volts, 70 volts, 80 volts, 90 volts or 99 volts.

According to the present invention, the positive temperature coefficient thermistor can be directly applied to circuit environments with higher working voltage requirements, and has high withstand voltage characteristics, and can be applied to 3C products, car lights or car motors. Furthermore, the 3C products include mobile phones or watches.

In one embodiment, the room temperature resistance of the positive temperature coefficient thermistor is greater than 0 ohm and less than 20 ohms, for example: 1 ohm, 3 ohms, 5 ohms, 7 ohms, 9 ohms, 11 ohms, 13 ohms, 15 ohms, 17 ohms or 19 ohms. Preferably, the room temperature resistance of the positive temperature coefficient thermistor is 6 ohms to 15 ohms.

According to the present invention, the room temperature resistance value is the room temperature resistance value of the positive temperature coefficient thermistor at 25°C.

Preferably, the contact rate of the plurality of particles is 20.5% to 37%, for example: 20.5, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36% or 37%. More preferably, the contact rate of the plurality of particles is 26.5% to 36.5%.

In one embodiment, the porosity of the ceramic sintered body is 21% to 45%, for example: 21%, 22%, 23%, 24%, 28%, 32%, 36%, 37%, 40%, 41%, 42%, 43%, 44% or 45%. Preferably, the porosity of the ceramic sintered body is 22.2% to 43.8%.

According to the present invention, by adjusting the porosity of the ceramic sintered body, the positive temperature coefficient thermistor can have the characteristics of high withstand voltage and low room temperature resistance.

In one embodiment, the composition of the ceramic sintered body further includes a semiconductor agent and silicon dioxide.

In one embodiment, based on the total weight of the ceramic sintered body, the content of the barium titanium oxide is 86 weight percent to 94.8 weight percent, for example, 86 weight percent, 88 weight percent, 90 weight percent, 92 weight percent, 94 weight percent or 94.8 weight percent; the content of the semiconductor chemical is 3.2 weight percent to 5 weight percent, for example, 3.2 weight percent, 3.5 weight percent, 3.8 weight percent, 4.1 weight percent, 4.4 weight percent, 4.7 weight percent or 5 weight percent; and the content of the silicon dioxide is 2 weight percent to 9 weight percent, for example, 2 weight percent, 4 weight percent, 6 weight percent, 8 weight percent or 9 weight percent.

Preferably, based on the total weight of the ceramic sintered body, the content of barium titanium oxide is 90 weight percent to 93.8 weight percent, the content of the semiconductor chemical is 3.6 weight percent to 4.9 weight percent, and the content of silicon dioxide is 2.5 weight percent to 5.5 weight percent. More preferably, based on the total weight of the ceramic sintered body, the content of barium titanium oxide is 90.5 weight percent to 93.5 weight percent, the content of the semiconductor chemical is 3.8 weight percent to 4.7 weight percent, and the content of silicon dioxide is 2.7 weight percent to 5.3 weight percent.

In one embodiment, the semiconductor chemical comprises yttrium, niobium, niobium, neodymium, niobium, alloys thereof, oxides thereof, or a combination thereof. Preferably, the semiconductor chemical comprises niobium oxide (Sm ₂ O ₃ ) and niobium oxide (Nb ₂ O ₅ ).

In one embodiment, based on the total weight of the ceramic sintered body, the content of tantalum oxide is 3 weight percent to 4.5 weight percent, and the content of niobium oxide is 0.2 weight percent to 0.5 weight percent.

In one embodiment, the average diameter of the plurality of particles is 2 microns to 3 microns. The average diameter is calculated by Scanning Probe Image Processor (SPIP) software.

The present invention also provides a ceramic composition comprising barium titanate, a semiconductor chemical and silicon dioxide, and based on the total weight of the ceramic composition, the content of the barium titanate is 86 weight percent to 94.8 weight percent, the content of the semiconductor chemical is 3.2 weight percent to 5 weight percent, and the content of the silicon dioxide is 2 weight percent to 9 weight percent.

According to the present invention, the ceramic composition and the components and their contents of the ceramic sintered body contained in the positive temperature coefficient thermistor are the same.

The present invention also provides a use of the ceramic composition for preparing the positive temperature coefficient thermistor.

The present invention also provides a ceramic sintered body, which is formed by sintering the ceramic composition; wherein the ceramic sintered body has a plurality of particles and a plurality of pores.

According to the present invention, the ceramic sintered body is the same as the ceramic sintered body contained in the positive temperature coefficient thermistor.

The present invention also provides a method for manufacturing a positive temperature coefficient thermistor, comprising: step a: mixing the ceramic composition and a solvent to form a ceramic slurry; step b: forming the ceramic slurry into a plurality of thin strips; step c: arranging an inner electrode strip on each of the plurality of thin strips to form a plurality of thin strips with inner electrode strips; step d: sequentially overlapping the plurality of thin strips with inner electrode strips to form a stacked structure; step e: sintering the plurality of thin strips in a reducing atmosphere; The ceramic body comprises a plurality of ceramic sintered bodies formed by sintering the plurality of thin strips and a plurality of internal electrodes formed by sintering the plurality of internal electrode strips, and the plurality of ceramic sintered bodies and the plurality of internal electrodes overlap each other; and step f: two external electrodes are respectively arranged on opposite sides of the ceramic body to obtain the positive temperature coefficient thermistor; wherein the two external electrodes are electrically connected to the plurality of internal electrodes.

In one embodiment, the step e comprises: step e1: sintering the laminated structure for 0.5 hours to 4 hours in the reducing atmosphere at a sintering temperature of 1000°C to 1500°C; and step e2: oxidizing the laminated structure at 660°C to 940°C in an atmospheric environment.

Preferably, the sintering temperature of step e1 is 1250°C to 1380°C, and the sintering time is 1 hour to 1.5 hours; and the oxidation treatment temperature of step e2 is 700°C to 900°C.

In summary, the positive temperature coefficient thermistor of the present invention has the characteristics of high withstand voltage and low room temperature resistance, and is competitive in the market.

10: Positive temperature coefficient thermistor

100: Ceramic body

110: Sintered ceramic body

120: Inner electrode

130,140: Side

150,160: Surface

200,300: External electrode

400: Protective layer

S:Thickness

Figure 1 is a schematic diagram of the cross section of the positive temperature coefficient thermistor of the present invention.

Figure 2 is a scanning electron microscope photograph of the ceramic sintered body in the cross section of the positive temperature coefficient thermistor of Example 3.

FIG3 is a scanning electron microscope photograph of a ceramic sintered body in a cross section of a positive temperature coefficient thermistor of Example 3 for calculating the contact rate.

FIG4 is a scanning electron microscope photograph of a ceramic sintered body in a cross section of a positive temperature coefficient thermistor in Example 3 for calculating porosity.

Several operation methods are provided below to illustrate the implementation of the present invention; those who are familiar with this art can easily understand the advantages and effects that can be achieved by the present invention through the contents of this manual, and make various modifications and changes without departing from the spirit of the present invention to implement or apply the contents of the present invention.

Preparation Example 1: Positive Temperature Coefficient Thermistor

The manufacturing method of each group of positive temperature coefficient thermistors is described as follows: First, perform step a: mix the ceramic composition and a solvent to form a ceramic slurry. Specifically, take barium titanate, semiconductor chemical and silicon dioxide according to the formulas of each group shown in Table 1 as starting materials, and use toluene and alcohol as solvents. The amount of solvent added can be adjusted according to the required degree of dispersion. A polymer dispersant (product model BYK-110, 111 and/or 115) is added in an amount of about 0.5 weight percent to 0.75 weight percent of the total weight of the starting materials, and a polyvinyl butyral resin binder is added in an amount of about 25 weight percent to 30 weight percent of the total weight of the starting materials, and the mixture is placed in a ball mill together with a zirconium ball and fully mixed by wet grinding to obtain a ceramic slurry.

Each set of semiconductor chemical agents includes niobium oxide (Sm ₂ O ₃ ) and niobium oxide (Nb ₂ O ₅ ), wherein: (1) the niobium oxide in Examples 1 to 3 is 0.35 weight percent, so the niobium oxide in Example 1 is 4.15 weight percent, and the niobium oxide in Examples 2 and 3 is 3.65 weight percent; and (2) the niobium oxide in Comparative Examples 1 to 4 is 0.1 weight percent, and the niobium oxide in Comparative Examples 1 to 4 is 0.4 weight percent.

Barium titanate, the semiconductor chemical and silicon dioxide are all commercial products; the average diameter of barium titanate is 0.5 micrometers to 0.7 micrometers; the average diameter of the semiconductor chemical is 1 micrometer to 2 micrometers; and the average diameter of silicon dioxide is 30 nanometers to 3 micrometers. The average diameter is obtained through particle size distribution analysis.

Second, proceed to step b: forming the ceramic slurry into multiple thin strips. Specifically, the ceramic slurry is formed into a sheet using a scraper method and then dried at a drying temperature of about 50 to 60°C to obtain a roll of thin strips. The drying time can be adjusted according to the actual situation.

Third, perform step c: an inner electrode tape is respectively arranged on the plurality of thin tapes to form a plurality of thin tapes with inner electrode tapes. Specifically, nickel metal powder and an organic binder are dispersed together in an organic solvent to prepare an inner electrode paste, and then the inner electrode tape is printed on the thin tape by screen printing to form a thin tape with an inner electrode tape; wherein the organic solvent contains toluene and alcohol.

Fourth, proceed to step d: sequentially overlap the plurality of thin strips with inner electrode strips to form a stacked structure. Specifically, thin strips without printed inner electrode strips are used as upper and lower covers, and thin strips with inner electrode strips are stacked to form a stacked structure. The stacked structure is placed between the upper cover and the lower cover for bonding, and after being evenly pressed with 75°C water, a cutting machine is used to cut out the ceramic green body.

Fifth, step e is performed: the stacked structure is sintered in a reducing atmosphere to form a ceramic body; wherein the ceramic body includes a plurality of ceramic sintered bodies formed by sintering the plurality of thin strips and a plurality of internal electrodes formed by sintering the plurality of internal electrode strips, and the plurality of ceramic sintered bodies and the plurality of internal electrodes are overlapped with each other. Specifically, the ceramic green body having the stacked structure is subjected to a degreasing treatment at about 300° C. for 24 hours in a protective atmosphere. The degreased ceramic green body is sintered at 1250°C to 1380°C for about 1 hour in a nitrogen/hydrogen reducing atmosphere to prepare a sintered ceramic body, which includes a plurality of ceramic sintered bodies sintered from the thin strips and a plurality of internal electrodes sintered from the plurality of internal electrode strips, and the plurality of ceramic sintered bodies and the plurality of internal electrodes overlap each other. The number of ceramic sintered body layers and the number of internal electrodes can be adjusted according to the thickness of the thin strips. Finally, the sintered ceramic body is rolled and polished, and then oxidized at 700°C to 900°C in an atmospheric environment to obtain the ceramic body.

Sixth, perform step f: arrange two external electrodes on opposite sides of the ceramic body to obtain the positive temperature coefficient thermistor; wherein the two external electrodes are electrically connected to the plurality of internal electrodes. Specifically, a protective layer is coated on the upper and lower surfaces of the ceramic body to form a protective layer parallel to the internal electrodes, and silver is attached to the left and right sides of the ceramic body to form external electrodes, and the external electrodes are electrically connected to the internal electrodes.

Finally, as shown in FIG. 1 , the positive temperature coefficient thermistor 10 has a ceramic body 100, which includes a plurality of ceramic sintered bodies 110 and a plurality of internal electrodes 120. The plurality of ceramic sintered bodies 110 and the plurality of internal electrodes 120 are overlapped and formed in the ceramic body 100; two external electrodes 200 and 300 are respectively disposed on the ceramic body 100. 00 on the opposite sides 130, 140, and electrically connected to the plurality of inner electrodes 120, and the angle between the two outer electrodes 200, 300 and the inner electrode 120 is about 90 degrees; and two protective layers 400, the two protective layers are respectively arranged on the upper and lower surfaces 150, 160 of the ceramic body 100, and are parallel to the plurality of inner electrodes 120. In addition, the two adjacent inner electrodes 120 are separated by the ceramic sintered body 110, and there is a thickness S between the two adjacent inner electrodes 120, and the thickness S is less than 40 microns.

Feature analysis:

The microstructure of the cross section of each group of positive temperature coefficient thermistors was observed with a scanning electron microscope to calculate the contact ratio and porosity. In addition, the withstand voltage and room temperature resistance of each group of positive temperature coefficient thermistors were measured, as described below.

1. Contact rate

(I) Sampling: After embedding each group of positive temperature coefficient thermistors, grind and polish to obtain a polished sample, and cut the polished sample with a dual beam focused ion beam (Dual Beam FIB, model: Thermo Fisher Scientific Helios 5) to obtain a cross section. The cross section is observed by back electron diffraction analysis technology in a scanning electron microscope (hardware model: Oxford Symmetry S2), and the scanning probe microscope image processing (Scanning Probe Image Processor, SPIP) software is used for calculation to select the cross-sectional field of view for analysis; wherein the cross-sectional field of view contains approximately 80 to 200 particles.

(II) Calculation of contact rate: Taking Example 3 as an example, its cross-sectional view is shown in Figure 2. Circle an area in the cross-sectional view, as shown in Figure 3, the area is colored, and the uncircled area is red. In the area, the sum of the perimeters of the plurality of particles (Lt), the sum of the perimeters of the plurality of holes (Lp), and the perimeter of the area (La) are measured by SPIP software, and the total contact length (Lc) of the plurality of particles is first obtained according to Formula I, and then the contact rate is obtained according to Formula II: Lc=(Lt-Lp-La)/2 (Formula I); and contact rate (%)=Lc/(Lc+Lp)×100 (Formula II). The results of each group are shown in Table 2.

2. Porosity

The same cross-sectional view as that used for calculating the contact rate is used. Taking Example 3 as an example, photoshop drawing software is used to convert the photo in Figure 2 into the photo shown in Figure 4, and the proportion of the black block to the total area of the photo is calculated using ImageJ software. The proportion of each group of black blocks to the total area of the photo is the porosity, and the results are shown in Table 2.

3. Withstand voltage value

The rated current and voltage are set according to the preset specifications of each group of positive temperature coefficient thermistors. After the current is fixed, the voltage is increased from 0V to the set voltage value of 24 volts in 180 seconds. If the positive temperature coefficient thermistor under test cannot withstand the voltage value of 24 volts, the set voltage value is gradually reduced until the positive temperature coefficient thermistor under test does not catch fire and burn due to the set voltage value. The test is considered to pass if the withstand voltage value (i.e. the withstand voltage value) is greater than 20 volts, and is considered to fail if the withstand voltage value is equal to or less than 20 volts.

4. Room temperature resistance value

The length of each group of tested samples is 0.933 mm, and the cross-sectional area is 2.396 ^mm2 . The room temperature resistance value is measured by applying voltage to the tested samples at room temperature (i.e. 25°C), and using a multimeter (brand: HIOKI, model: RM3545) to measure the current value to convert the resistance value. The results of each group are shown in Table 2.

From Table 2, it can be seen that, first, the contact rate of Examples 1 to 3 is 26.98% to 36.1%, and the withstand voltage value is 24V, which has the characteristics of high withstand voltage. In contrast, the contact rate of Comparative Example 1 is as high as 43.25%, and as shown in Comparative Examples 1 to 4, as the contact rate increases, the withstand voltage value gradually decreases. It can be seen that controlling the contact rate to 26.98% to 36.1% can make the positive temperature coefficient thermistor have the characteristics of high withstand voltage.

Second, the porosity of Examples 1 to 3 is 24.7% to 39.8%, and the withstand voltage value is 24V, which has the characteristics of high withstand voltage. In contrast, the porosity of Comparative Example 1 is only 16%, and as shown in Comparative Examples 1 to 4, as the porosity decreases, the withstand voltage value gradually decreases. It can be seen that controlling the porosity to 26.98% to 36.1% can make the positive temperature coefficient thermistor have the characteristics of high withstand voltage.

Third, from the comparison between Example 3 and Comparative Example 1, it can be seen that when the silicon dioxide is fixed at 5 weight percent, the semiconductor chemical is reduced from 4 weight percent in Example 3 to 0.5 weight percent in Comparative Example 1, and the barium titanate content is increased accordingly, the withstand voltage value of the positive temperature coefficient thermistor will be reduced. It can be seen that insufficient semiconductor chemical content will increase the contact rate and reduce the porosity, and reduce the withstand voltage value of the positive temperature coefficient thermistor.

Fourth, from the comparison of Comparative Examples 1 to 4, it can be seen that when silicon dioxide is used to replace barium titanate and the silicon dioxide content is gradually increased, the withstand voltage value of the positive temperature coefficient thermistor will be reduced. It can be seen that when the silicon dioxide content is too high and the semiconductor chemical content is insufficient, the contact rate will be increased and the porosity will be reduced, and the withstand voltage value of the positive temperature coefficient thermistor will be reduced.

Finally, from the comparison between Example 1 and Example 2, it can be seen that when the semiconductor chemical content is increased and the barium titanate content is correspondingly reduced, the room temperature resistance value of the positive temperature coefficient thermistor will be increased. In other words, the semiconductor chemical content should not be too high, otherwise it will increase the room temperature resistance value of the positive temperature coefficient thermistor, increase daily energy consumption or reduce the current flow in the circuit.

In summary, the positive temperature coefficient thermistor of the present invention has the characteristics of high withstand voltage and low room temperature resistance, and is competitive in the market.

10: Positive temperature coefficient thermistor

100: Ceramic body

110: Sintered ceramic body

120: Inner electrode

130,140: Side

150,160: Surface

200,300: External electrode

400: Protective layer

S:Thickness

Claims (8)

A positive temperature coefficient thermistor, comprising: a ceramic body and two external electrodes, wherein the two external electrodes are respectively arranged on opposite sides of the ceramic body; the ceramic body comprises a ceramic sintered body and an internal electrode overlapping each other; the ceramic sintered body has a plurality of particles and a plurality of pores, and the composition of the ceramic sintered body comprises barium titanate; and The contact rate of the plurality of particles is 20% to 37.5%; wherein the contact rate is obtained by observing a cross section of the positive temperature coefficient thermistor with a scanning electron microscope and circling an area. In the area, the sum of the perimeters of the plurality of particles (Lt), the sum of the perimeters of the plurality of holes (Lp), and the perimeter of the area (La) are measured, and then the total contact length (Lc) of the plurality of particles is obtained according to Formula I, and then the contact rate is obtained according to Formula II: Lc=(Lt-Lp-La)/2 (Formula I); and Contact rate (%)=Lc/(Lc+Lp) × 100 (Formula II). A positive temperature coefficient thermistor as described in claim 1, wherein the porosity of the ceramic sintered body is 21% to 45%. A positive temperature coefficient thermistor as described in claim 1, wherein the composition of the ceramic sintered body further includes a semiconductor chemical and silicon dioxide, and based on the total weight of the ceramic sintered body, the content of barium titanium oxide is 86 weight percent to 94.8 weight percent, the content of the semiconductor chemical is 3.2 weight percent to 5 weight percent, and the content of silicon dioxide is 2 weight percent to 9 weight percent. A positive temperature coefficient thermistor as described in claim 3, wherein the semiconductor chemical comprises yttrium, samarium, niobium, neodymium, niobium, their alloys, their oxides, or any one or a combination thereof. A positive temperature coefficient thermistor as described in claim 1, wherein the withstand voltage of the positive temperature coefficient thermistor is greater than 20 volts and less than 100 volts, and the room temperature resistance value of the positive temperature coefficient thermistor is greater than 0 ohm and less than 20 ohms. A method for manufacturing a positive temperature coefficient thermistor as described in claim 1, comprising: Step a: mixing a ceramic composition and a solvent to form a ceramic slurry, wherein the ceramic composition comprises barium titanate, a semiconductor chemical and silicon dioxide, and based on the total weight of the ceramic composition, the content of barium titanate is 86 weight percent to 94.8 weight percent, the content of the semiconductor chemical is 3.2 weight percent to 5 weight percent, and the content of silicon dioxide is 2 weight percent to 9 weight percent; Step b: forming the ceramic slurry into a plurality of thin strips; Step c: respectively providing an inner electrode strip on the plurality of thin strips to form a plurality of thin strips with inner electrode strips; Step d: sequentially stacking the plurality of thin strips with inner electrode strips to form a stacked structure; Step e: sintering the stacked structure in a reducing atmosphere to form the ceramic body; and Step f: respectively placing the two outer electrodes on opposite sides of the ceramic body to obtain the positive temperature coefficient thermistor; wherein the two outer electrodes are electrically connected to the plurality of inner electrodes. The manufacturing method as described in claim 6, wherein the step e comprises: Step e1: sintering the laminated structure in the reducing atmosphere for 0.5 hours to 4 hours at a sintering temperature of 1000°C to 1500°C and Step e2: oxidizing the laminated structure at 660°C to 940°C in an atmospheric environment. A manufacturing method as described in claim 7, wherein the sintering temperature of step e1 is 1250°C to 1380°C, and the sintering time is 1 hour to 1.5 hours; and the oxidation treatment temperature of step e2 is 700°C to 900°C.