Rare earth doped PTC thermistor slurry and preparation method thereof

Abstract

The invention discloses rare earth doped PTC thermistor paste and a preparation method thereof, and belongs to the technical field of electronic paste in electronic information materials. The rare earth doped PTC thermistor paste comprises the following components in percentage by mass: 70wt%-90wt% of a solid phase and 10wt%-30wt% of an organic carrier, the solid phase is prepared from the following components in percentage by mass: 40wt%-70wt% of a composite functional phase, 30wt%-58wt% of a glass phase and 0wt%-2wt% of a doping phase; the composite functional phase comprises RuO2 and CuO, and the doping phase is La2O3. According to the invention, CuO and RuO2 are subjected to a high-temperature reaction to synthesize a composite functional phase, and La2O3 is doped as a conductive phase, so that the obtained PTC thermistor paste is stable in resistance value, high and adjustable in resistance temperature coefficient and high and adjustable in sheet resistance, and the problems of low resistance temperature coefficient, unstable resistance value, low sheet resistance and the like of the traditional PTC thermistor paste are solved.

Description

Technical Field

[0001] The invention relates to a rare earth doped PTC thermistor slurry and a preparation method thereof, belonging to the technical field of electronic slurry in electronic information materials. Background Art

[0002] As an important foundation for the development of the electronic information industry, the new generation of electronic components is developing towards high integration, lightweight, intelligent and green. Therefore, the demand for PTC thermistor paste is increasing, and the performance requirements are getting higher and higher.

[0003] At present, the widely used PTC thermistor materials mainly include barium titanate-based semiconductor ceramics, precious metal platinum, and sputtered metal copper. Barium titanate is made semiconductor by valence control. The resistivity of the material suddenly increases by 3-4 orders of magnitude as the temperature rises, showing a thermal effect. However, due to the defects of the material itself, the performance of the thermistor is also insufficient. The resistance temperature coefficient of the precious metal platinum thermistor is linear, but the cost is high and it is not suitable for general application. The resistance temperature coefficient of the copper thermistor is relatively high, and because copper is easily oxidized, it is generally used in low temperature environments.

[0004] To meet the development needs of information technology and core component manufacturing, thermistors are developing in the direction of chip-type, high reliability, light, small and thin. Thick film process technology is the main means to achieve miniaturization and micro-miniaturization of electronic products. The thick film screen printing method for preparing PTC thermistor paste has the advantages of fast response, adjustable resistance value and adjustable film thickness. Looking at the entire PTC thermistor paste, there are generally problems such as low resistance temperature coefficient, poor stability, uneven power density and environmental pollution. Summary of the invention

[0005] In order to overcome the problems in the background technology, the purpose of the present invention is to provide a rare earth doped PTC thermistor slurry and a preparation method thereof. The prepared rare earth doped PTC thermistor slurry has high and adjustable resistance temperature coefficient, high and adjustable square resistance, stable and reliable resistance value, good printing and sintering characteristics, and good sintering matching effect with alumina insulator.

[0006] In order to achieve the above object, the present invention is implemented by the following technical solutions:

[0007] A rare earth doped PTC thermistor slurry comprises the following components in percentage by weight: 70wt%-90wt% solid phase and 10wt%-30wt% organic carrier; the solid phase comprises the following components in percentage by weight: 40wt%-70wt% composite functional phase, 30wt%-58wt% glass phase and 0wt%-2wt% doped phase; the composite functional phase comprises RuO 2 and CuO, doped with La 2O 3 .

[0008] More preferably, the RuO 2 The molar ratio of CuO is 1:1.

[0009] More preferably, the particle size of the CuO is less than 11 μm; 2 The specific surface area is 20m 2 / g-30m 2 / g, and the particle size is less than 14μm.

[0010] More preferably, the glass phase is calcium borosilicate glass-ceramic powder with a softening temperature of 600-800° C. and a particle size of less than 12 μm.

[0011] More preferably, the calcium borosilicate glass powder comprises the following components in percentage by weight: CaO 10wt%-30wt%, B 2 O 3 10wt%-30wt%, SiO 2 10wt%-35wt%, Al 2 O 3 0wt%-10wt%, BaO 0wt%-5wt%, ZnO0wt%-10wt%, Na 2 O 0wt%-10wt%, K 2 O 0wt%-5wt%, TiO 2 0wt%-1wt%, MgO 0wt%-5wt% and Li 2 O 0wt%-1wt%.

[0012] More preferably, the organic carrier includes a solvent, a thickener, a surfactant and a thixotropic agent; the solvent is at least one of terpineol, tributyl citrate and diethylene glycol butyl ether; the thickener is at least one of ethyl cellulose, polyvinyl alcohol and hydroxyethyl cellulose; the surfactant is at least one of Span 85 and lecithin; and the thixotropic agent is hydrogenated castor oil or polyamide wax.

[0013] More preferably, the method for preparing the rare earth doped PTC thermistor slurry comprises the following steps:

[0014] (1) According to RuO 2 and CuO were ball-milled with anhydrous ethanol as the medium, dried and calcined, cooled to room temperature, and then ball-milled again, and then taken out and dried to obtain a composite functional phase;

[0015] (2) mixing an organic solvent, a thickener, a thixotropic agent and a surfactant, and heating and dissolving them to obtain an organic carrier;

[0016] (3) The composite functional phase, glass powder, organic carrier and doping phase are mixed uniformly and rolled to obtain rare earth doped PTC thermistor slurry.

[0017] Beneficial effects of the present invention: The present invention adopts CuO, RuO 2 High temperature reaction to synthesize the composite functional phase, followed by La doping 2 O 3 As a conductive phase, it obtains stable resistance, high and adjustable resistance temperature coefficient, and high and adjustable square resistance, solving the problems of low resistance temperature coefficient, unstable resistance, and low square resistance of traditional PTC thermistor slurry. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the printed pattern of the thick film resistor of the present invention.

[0019] Figure 2 The resistance temperature coefficient and ambient temperature variation curve of the rare earth doped PTC thermistor slurry prepared in Examples 1-5 of the present invention.

[0020] Figure 3 The TCR and square resistance diagram of the rare earth doped PTC thermistor slurry prepared in Examples 1-5 of the present invention. DETAILED DESCRIPTION

[0021] The present invention is further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0022] Example 1

[0023] A method for preparing a rare earth doped PTC thermistor slurry comprises the following steps:

[0024] (1) Preparation of composite functional phase of PTC thermistor slurry: Selected RuO 2 The specific surface area of ​​the powder is 20m 2 / g-30m 2 / g, the particle size is less than 10μm, the particle size of CuO is less than 10μm and La 2 O 3 , prepared according to the following method: weigh RuO in a 1:1 molar ratio 2 and CuO, ball-milled with anhydrous ethanol as the medium for 8 hours, dried, placed in a high-temperature muffle furnace at 1100°C for reaction for 8 hours, cooled with the furnace, continued ball-milling for 10 hours, taken out and dried to obtain the composite functional phase.

[0025] (2) Preparation of glass phase: CaO 25wt%, B 2 O 3 25wt%, SiO 2 20wt%,Al 2O 3 5wt%, BaO 2wt%, ZnO 8wt%, Na 2 O 5wt%, K 2 O 5wt%, TiO 2 1wt%, MgO 3wt% and Li 2 After mixing evenly, put it into a melting furnace and keep it at 1400℃ for 2h, then quickly quench it with water to get glass residue, use anhydrous ethanol as the medium, ball mill the glass residue for 15h in a ball mill, filter and dry it to get calcium borosilicate glass powder.

[0026] (3) Preparation of organic carrier: 56wt%, 20wt%, 20wt% and 3wt% of terpineol, diethylene glycol butyl ether acetate, tributyl citrate and ethyl cellulose were weighed respectively in a beaker and heated in a water bath at 80°C with stirring until the ethyl cellulose solvent was dissolved. Then, 0.5wt% of hydrogenated castor oil and 0.5wt% of Span 85 were added and continued to heat and stir for 1h, and then cooled naturally to room temperature.

[0027] (4) Preparation of PTC thermistor slurry: The solid material prepared above with the contents of the composite functional phase, glass phase and lanthanum oxide of 55wt%, 45wt% and 0wt% respectively was ball-milled and then uniformly mixed with the solid material and the organic carrier, wherein the solid material content was 78wt% and the organic carrier content was 22wt%, and then rolled 4 times with a three-roll mill to prepare rare earth doped PTC thermistor slurry.

[0028] Example 2

[0029] A method for preparing a rare earth doped PTC thermistor slurry comprises the following steps:

[0030] (1) Preparation of composite functional phase of PTC thermistor slurry: Selected RuO 2 The specific surface area of ​​the powder is 20m 2 / g-30m 2 / g, the particle size is less than 14μm, the particle size of CuO is less than 10μm and La 2 O 3 , prepared according to the following method: weigh RuO in a 1:1 molar ratio 2 and CuO, ball-milled for 6 hours with anhydrous ethanol as the medium, dried, placed in a high-temperature muffle furnace at 900°C for reaction for 10 hours, cooled with the furnace, continued ball-milling for 12 hours, taken out and dried to obtain the composite functional phase.

[0031] (2) Preparation of glass phase: CaO 13wt%, B 2 O 3 30wt%, SiO 2 10wt%,Al2 O 3 10wt%, BaO 5wt%, ZnO 10wt%, Na 2 O 10wt%, K 2 O 5wt%, TiO 2 1wt%, MgO 5wt% and Li 2 O 1wt%, mixed evenly and put into a melting furnace, kept at 1300℃ for 1h, then quickly quenched with water to obtain glass residue, ball milled the glass residue with anhydrous ethanol for 15h, filtered and dried to obtain calcium borosilicate glass powder.

[0032] (3) Preparation of organic carrier: 56wt%, 20wt%, 20wt% and 3wt% of terpineol, diethylene glycol butyl ether acetate, tributyl citrate and ethyl cellulose were weighed respectively in a beaker and heated in a water bath at 80°C with stirring until the ethyl cellulose solvent was dissolved. Then, 0.5wt% of hydrogenated castor oil and 0.5wt% of Span 85 were added and continued to heat and stir for 1h, and then cooled naturally to room temperature.

[0033] (4) Preparation of PTC thermistor slurry: The solid material prepared above with the contents of the composite functional phase, glass phase and lanthanum oxide being 55wt%, 44.5wt% and 0.5wt% respectively was ball-milled and then the solid material and the organic carrier were mixed evenly, wherein the solid material content was 78wt% and the organic carrier content was 22wt%, and then rolled 5 times with a three-roll mill to prepare rare earth doped PTC thermistor slurry.

[0034] Example 3

[0035] A method for preparing a rare earth doped PTC thermistor slurry comprises the following steps:

[0036] (1) Preparation of composite functional phase of PTC thermistor slurry: Selected RuO 2 The specific surface area of ​​the powder is 20m 2 / g-30m 2 / g, the particle size is less than 14μm, the particle size of CuO is less than 10μm and La 2 O 3 , prepared according to the following method: weigh RuO in a 1:1 molar ratio 2 and CuO, ball-milled with anhydrous ethanol as the medium for 10 hours, dried, placed in a high-temperature muffle furnace at 1200℃ for reaction for 6 hours, cooled with the furnace, continued ball-milling for 8 hours, taken out and dried to obtain the composite functional phase.

[0037] (2) Preparation of glass phase: CaO 30wt%, B 2 O 3 10wt%, SiO2 35wt%,Al 2 O 3 10wt%, BaO 5wt% and ZnO 10wt%, mix them evenly and put them into a melting furnace, keep them at 1300℃-1500℃ for 2h, then quickly quench them with water to get glass residue, use anhydrous ethanol as the medium, ball mill the glass residue for 15h in a ball mill, filter and dry them to get calcium borosilicate glass powder.

[0038] (3) Preparation of organic carrier: 56wt%, 20wt%, 20wt% and 3wt% of terpineol, diethylene glycol butyl ether acetate, tributyl citrate and ethyl cellulose were weighed respectively in a beaker and heated in a water bath at 80°C with stirring until the ethyl cellulose solvent was dissolved. Then, 0.5wt% of hydrogenated castor oil and 0.5wt% of Span 85 were added and continued to heat and stir for 1h, and then cooled naturally to room temperature.

[0039] (4) Preparation of PTC thermistor slurry: The solid material prepared above with the contents of the composite functional phase, glass phase and lanthanum oxide of 54.5%, 44.5% and 1wt% respectively was ball-milled and then uniformly mixed with the solid material and the organic carrier, wherein the solid material content was 78wt% and the organic carrier content was 22wt%, and then rolled 3-5 times with a three-roll mill to prepare rare earth doped PTC thermistor slurry.

[0040] Example 4

[0041] A method for preparing a rare earth doped PTC thermistor slurry comprises the following steps:

[0042] (1) Preparation of composite functional phase of PTC thermistor slurry: Selected RuO 2 The specific surface area of ​​the powder is 20m 2 / g-30m 2 / g, the particle size is less than 14μm, the particle size of CuO is less than 10μm and La 2 O 3 , prepared according to the following method: weigh RuO in a 1:1 molar ratio 2 and CuO, ball-milled with anhydrous ethanol as the medium for 10 hours, dried, placed in a high-temperature muffle furnace at 1200℃ for reaction for 6 hours, cooled with the furnace, continued ball-milling for 8 hours, taken out and dried to obtain the composite functional phase.

[0043] (2) Preparation of glass phase: CaO 25wt%, B 2 O 3 25wt%, SiO 2 20wt%,Al 2 O 3 5wt%, BaO 2wt%, ZnO 8wt%, Na2 O 5wt%, K 2 O 5wt%, TiO 2 1wt%, MgO 3wt% and Li 2 The mixture is mixed evenly and put into a melting furnace and kept at 1300-1500°C for 2 hours. The mixture is then quickly quenched with water to obtain glass residue. The glass residue is ball milled in anhydrous ethanol for 15 hours. The mixture is filtered and dried to obtain calcium borosilicate glass powder.

[0044] (3) Preparation of organic carrier: 56wt%, 20wt%, 20wt% and 3wt% of terpineol, diethylene glycol butyl ether acetate, tributyl citrate and ethyl cellulose were weighed respectively in a beaker and heated in a water bath at 80°C with stirring until the ethyl cellulose solvent was dissolved. Then, 0.5wt% of hydrogenated castor oil and 0.5wt% of Span 85 were added and continued to heat and stir for 1h, and then cooled naturally to room temperature.

[0045] (4) Preparation of PTC thermistor slurry: The solid material prepared above with the contents of the composite functional phase, glass phase and lanthanum oxide being 54.5%, 44% and 1.5wt% respectively was ball-milled and then uniformly mixed with the solid material and the organic carrier, wherein the solid material content was 78wt% and the organic carrier content was 22wt%, and then rolled 3-5 times with a three-roll mill to prepare rare earth doped PTC thermistor slurry.

[0046] Example 5

[0047] A method for preparing a rare earth doped PTC thermistor slurry comprises the following steps:

[0048] (1) Preparation of composite functional phase of PTC thermistor slurry: Selected RuO 2 The specific surface area of ​​the powder is 20m 2 / g-30m 2 / g, the particle size is less than 10μm, the particle size of CuO is less than 10μm and La 2 O 3 , prepared according to the following method: weigh RuO in a 1:1 molar ratio 2 and CuO, after ball milling for 8h-12h, put it into a high-temperature muffle furnace at 1100℃ for reaction for 8h, cool it with the furnace, and crush it by ball milling to obtain the composite functional phase.

[0049] (2) Preparation of glass phase: CaO 25wt%, B 2 O 3 25wt%, SiO 2 20wt%,Al 2 O 3 5wt%, BaO 2wt%, ZnO 8wt%, Na2 O 5wt%, K 2 O 5wt%, TiO 2 1wt%, MgO 3wt% and Li 2 The mixture is mixed evenly and put into a melting furnace and kept at 1300-1500°C for 2 hours. The mixture is then quickly quenched with water to obtain glass residue. The glass residue is ball milled in anhydrous ethanol for 15 hours. The mixture is filtered and dried to obtain calcium borosilicate glass powder.

[0050] (3) Preparation of organic carrier: 56wt%, 20wt%, 20wt% and 3wt% of terpineol, diethylene glycol butyl ether acetate, tributyl citrate and ethyl cellulose were weighed respectively in a beaker and heated in a water bath at 80°C with stirring until the ethyl cellulose solvent was dissolved. Then, 0.5wt% of hydrogenated castor oil and 0.5wt% of Span 85 were added and continued to heat and stir for 1h, and then cooled naturally to room temperature.

[0051] (4) Preparation of PTC thermistor slurry: The solid material prepared above with the contents of the composite functional phase, glass phase and lanthanum oxide being 54wt%, 44wt% and 2wt% respectively was ball-milled and then uniformly mixed with the solid material and the organic carrier, wherein the solid material content was 78wt% and the organic carrier content was 22wt%, and then rolled 3-5 times with a three-roll mill to prepare rare earth doped PTC thermistor slurry.

[0052] Comparative Example 1

[0053] A method for preparing a rare earth doped PTC thermistor slurry comprises the following steps:

[0054] (1) Preparation of composite functional phase of PTC thermistor slurry: Selected RuO 2 The specific surface area of ​​the powder is 20m 2 / g-30m 2 / g, the particle size is less than 10μm, the particle size of CuO is less than 10μm and La 2 O 3 , prepared according to the following method: a certain weight portion of RuO 2 , CuO and La 2 O 3 After ball milling for 8 hours with anhydrous ethanol as the medium and drying, it is placed in a high-temperature muffle furnace at 1100°C for reaction for 8 hours, cooled with the furnace, and continued to ball mill for 10 hours. The composite functional phase is obtained by taking out and drying.

[0055] (2) Preparation of glass phase: CaO 25wt%, B 2 O 3 25wt%, SiO 2 20wt%,Al 2 O3 5wt%, BaO 2wt%, ZnO 8wt%, Na 2 O 5wt%, K 2 O 5wt%, TiO 2 1wt%, MgO 3wt% and Li 2 After mixing evenly, put it into a melting furnace and keep it at 1400℃ for 2h, then quickly quench it with water to get glass residue, use anhydrous ethanol as the medium, ball mill the glass residue for 15h in a ball mill, filter and dry it to get calcium borosilicate glass powder.

[0056] (3) Preparation of organic carrier: Weigh terpineol and ethyl cellulose according to their mass percentages in a beaker and heat and stir in a water bath at 80°C until the ethyl cellulose solvent is dissolved. Then add hydrogenated castor oil and Span 85 and continue heating and stirring for 1 hour, and then cool naturally to room temperature.

[0057] (4) Preparation of PTC thermistor slurry: The solid material prepared above with the content of the composite functional phase and the glass phase being 55wt% and 45wt% respectively was ball-milled and then uniformly mixed with the solid material and the organic carrier, wherein the solid material content was 78wt% and the organic carrier content was 22wt%, and then rolled 4 times with a three-roll mill to prepare rare earth doped PTC thermistor slurry.

[0058] Comparative Example 2

[0059] A method for preparing a rare earth doped PTC thermistor slurry comprises the following steps:

[0060] (1) Preparation of composite functional phase of PTC thermistor slurry: Selected RuO 2 The specific surface area of ​​the powder is 20m 2 / g-30m 2 / g, the particle size is less than 14μm, the particle size of CuO is less than 10μm and Y 2 O 3 , prepared according to the following method: weigh RuO 2 and CuO, ball-milled for 6 hours with anhydrous ethanol as the medium, dried, placed in a high-temperature muffle furnace at 900°C for reaction for 10 hours, cooled with the furnace, continued ball-milling for 12 hours, taken out and dried to obtain the composite functional phase.

[0061] (2) Preparation of glass phase: CaO 13wt%, B 2 O 3 30wt%, SiO 2 10wt%,Al 2 O 3 10wt%, BaO 5wt%, ZnO 10wt%, Na 2O 10wt%, K 2 O 5wt%, TiO 2 1wt%, MgO 5wt% and Li 2 O 1wt%, mixed evenly and put into a melting furnace, kept at 1300℃ for 1h, then quickly quenched with water to obtain glass residue, ball milled the glass residue with anhydrous ethanol for 15h, filtered and dried to obtain calcium borosilicate glass powder.

[0062] (3) Preparation of organic carrier: Weigh terpineol and ethyl cellulose according to their mass percentages in a beaker and heat and stir in a water bath at 80°C until the ethyl cellulose solvent is dissolved. Then add hydrogenated castor oil and Span 85 and continue heating and stirring for 1 hour, and then cool naturally to room temperature.

[0063] (4) Preparation of PTC thermistor slurry: Prepare the composite functional phase, glass phase, Y 2 O 3 The solid material was uniformly milled with the contents of 55wt%, 44.5wt% and 0.5wt% respectively. The solid material and the organic carrier were then uniformly mixed, wherein the solid material content was 70wt% and the organic carrier content was 30wt%, and then rolled 5 times with a three-roll mill to prepare rare earth doped PTC thermistor slurry.

[0064] Effect example

[0065] The resistor pastes prepared in the above examples 1-5 and comparative examples 1-2 were prepared according to Figure 1 The resistor paste is printed on the alumina ceramic substrate with printed electrodes using a thick film screen printing process, and then dried in a drying oven, placed in a sintering furnace, heated to 850℃±5℃ at a rate of 10℃ / min, and kept warm for 10min. The sample is cooled to room temperature with the furnace to be prepared. The thickness of the resistor paste on the alumina ceramic substrate is 18μm.

[0066] Square resistance test: square resistance is tested according to the international GB / T 17472.3-1998 regulations. Figure 1 For the test diagram shown, place the electrode of the resistance meter on the electrode area of ​​the sample to be tested, and make good contact. Measure each measurement point three times and take the average value. The calculation of the square resistance test result is shown in (1-1):

[0067]

[0068] Where: R S is the square resistance value; R is the resistance value of the square number 100; w is the width of the film thickness 1mm; l is the length of the thick film 100mm.

[0069] Temperature coefficient of resistance (TCR) test: Figure 1Weld a certain length of wire to the electrode area of ​​the test sample, place the sample to be tested on the heating table, and then connect the other end of the wire to the resistance tester. The test temperature is 25℃-125℃. The calculation formula for the resistance temperature coefficient is shown in 1-2:

[0070]

[0071] Where: R 1 T 1 Resistance at temperature, R 2 T 2 Resistance at temperature, T 1 T 1 Test temperature, T 2 T 2 Test temperature.

[0072] The test results of resistance and resistance temperature coefficient are shown in Table 1. They are compared with commercial thick film PTC thermistor pastes at home and abroad (thick film resistor paste 2612-I type from ESI of the United States and R-12P type from Xi'an Xinbei Electronic Technology Co., Ltd. of China, square resistance 100±20%Ω / □, TCR 2200±10%ppm / ℃).

[0073] Table 1 shows the properties of the slurry at 125°C

[0074]

[0075] The PTC thermistor slurry prepared by the present invention increases the square resistance and the temperature coefficient of resistance with the increase of the rare earth lanthanum oxide doping amount. The linear relationship between the square resistance and the temperature coefficient of resistance is R 2 As high as 0.99. The better the linear relationship between square resistance and temperature coefficient of resistance, the better the material can avoid large fluctuations in resistance value and performance drift due to temperature fluctuations, which is convenient for accurate calibration of circuit design. A good linear relationship can ensure that the resistance value changes of the resistor at different temperatures are in line with expectations, thereby reducing the impact of temperature changes on instrument performance and enabling the instrument to operate more stably. Therefore, the linear relationship of Examples 1-5 is better than that of Comparative Examples 1-2, indicating that the resistor slurry prepared in Examples 1-5 has good stability and reliability, and can meet the application of advanced electronic equipment that is sensitive to temperature changes and has strict requirements.

[0076] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. A rare earth doped PTC thermistor slurry, characterized in that: It includes the following components in mass percentage: 70wt%-90wt% solid phase and 10wt%-30wt% organic carrier; the solid phase includes the following components in mass percentage: 40wt%-70wt% composite functional phase, 30wt%-58wt% glass phase and 0wt%-2wt% doped phase; the composite functional phase includes RuO2 and CuO, and the doped phase is La2O3.

2. The rare earth doped PTC thermistor slurry according to claim 1, characterized in that: More preferably, the molar ratio of RuO2 to CuO is 1:

1.

3. The rare earth doped PTC thermistor slurry according to claim 1, characterized in that: The particle size of the CuO is less than 11 μm; the specific surface area of ​​the RuO2 is 20 m 2 / g-30m 2 / g, and the particle size is less than 14μm.

4. The rare earth doped PTC thermistor slurry according to claim 1, characterized in that: The glass phase is calcium borosilicate glass powder, with a softening temperature of 600-800° C. and a particle size of less than 12 μm.

5. The rare earth doped PTC thermistor slurry according to claim 1, characterized in that: The calcium borosilicate glass powder includes the following components in percentage by mass: CaO 10wt%-30wt%, B2O3 10wt%-30wt%, SiO2 10wt%-35wt%, Al2O3 0wt%-10wt%, BaO 0wt%-5wt%, ZnO 0wt%-10wt%, Na2O 0wt%-10wt%, K2O 0wt%-5wt%, TiO2 0wt%-1wt%, MgO 0wt%-5wt% and Li2O 0wt%-1wt%.

6. The rare earth doped PTC thermistor slurry according to claim 1, characterized in that: The organic carrier comprises a solvent, a thickener, a surfactant and a thixotropic agent; the solvent is at least one of terpineol, tributyl citrate and diethylene glycol butyl ether; the thickener is at least one of ethyl cellulose, polyvinyl alcohol and hydroxyethyl cellulose; the surfactant is at least one of Span 85 and lecithin; and the thixotropic agent is hydrogenated castor oil or polyamide wax.

7. The method for preparing the rare earth doped PTC thermistor slurry according to any one of claims 1 to 6, characterized in that: The steps include: (1) ball milling RuO2 and CuO using anhydrous ethanol as a medium, drying and calcining, cooling to room temperature, continuing ball milling, taking out and drying to obtain a composite functional phase; (2) mixing an organic solvent, a thickener, a thixotropic agent and a surfactant, and heating and dissolving them to obtain an organic carrier; (3) The composite functional phase, glass powder, organic carrier and doping phase are mixed uniformly and rolled to obtain rare earth doped PTC thermistor slurry.

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