Flexible temperature sensor and method of manufacturing the same

Abstract

The present application relates to the technical field of flexible sensing, in particular to a flexible temperature sensor and a preparation method thereof. The flexible temperature sensor provided by the present application comprises a base film, a sensing material electrode embedded in the base film, and a packaging layer. The sensing material electrode is a silver-gallium alloy. The sensing electrode of the flexible temperature sensor provided by the present application is almost completely embedded in the base film, which can be better combined with the base to improve the mechanical properties and measurement stability of the flexible sensor. Meanwhile, the embedded base type flexible temperature sensor has a simple structure and can be prepared in a large area at a low cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of flexible sensing, in particular to a flexible temperature sensor and a preparation method thereof. BACKGROUND

[0002] In recent years, with the continuous improvement of people's living standards, people's requirements for sensors are also increasing. Traditional rigid sensors have been difficult to meet the increasingly diversified application scenarios due to their large size, inability to bend and other shortcomings. Flexible sensors have good bending performance, can be closely attached to irregular surfaces, are light and thin in structure, and enhance the comfort and universality of sensor wearing. These characteristics make flexible sensors have broad application prospects in wearable electronics, health care, agricultural monitoring and other fields.

[0003] The key of flexible sensor technology lies in sensing materials and preparation process. At present, commonly used flexible sensing materials include liquid metal, graphene oxide, silver nanowire, copper nanowire, etc., but there are still shortcomings such as high cost and poor stability; in the key preparation process technology, mainly including patterning preparation technology, transfer printing technology, etc., however, there are still shortcomings such as high cost, high sintering temperature, inability to prepare large area, poor mechanical properties, etc. SUMMARY

[0004] In order to solve the above technical problems, the present application provides a flexible temperature sensor and a preparation method thereof.

[0005] In a first aspect, the present application provides a flexible temperature sensor, comprising:

[0006] a base film;

[0007] a sensing material electrode embedded in the base film;

[0008] and a packaging layer;

[0009] The sensing electrode material is a silver-gallium alloy.

[0010] The flexible temperature sensor based on liquid metal gallium coating provided by the present application is an embedded base type flexible temperature sensor, which includes a base film as a flexible sensor base, a sensing material electrode embedded in the base film for sensing temperature changes, and a packaging layer for packaging. The sensing electrode of the flexible temperature sensor provided by the present application is almost completely embedded in the base film, which can better combine with the base and improve the mechanical properties and measurement stability of the flexible sensor. The embedded base type flexible temperature sensor has a simple structure and can be prepared in a large area conveniently and at low cost.

[0011] Preferably, the sensing electrode material is liquid metal gallium coated silver electrode, the thickness of the sensing electrode material is 5-10 um, preferably 7-10 um; preferably, the base film is polyimide film; the thickness of the base film is not more than 40 um, preferably 23-40 um, more preferably 25-40 um.

[0012] In the present application, the base film is polyimide film used as the base of the flexible sensor, and the flexible sensing material is gallium-silver alloy formed by liquid metal gallium coated silver particles with high surface activity, which is combined with screen printing and other transfer methods to better embed in the ultra-thin polyimide base film, and can better solve the problems of high sintering temperature, poor stability, easy damage, high preparation cost, and inability to prepare large area of flexible sensor. Especially, the combination of liquid metal gallium coated silver electrode with a specific thickness and polyimide film with a specific thickness makes the flexible sensor more closely combined, and can better improve the mechanical properties and measurement stability of the flexible sensor and reduce the cost.

[0013] Further preferably, the sensing electrode material is embedded in the base film, and the (upper) surface of the sensing electrode material is preferably flush with the (upper) surface of the base film, and preferably the (upper) surface of the sensing electrode material is exposed outside the base film. Further preferably, the (upper) surface of the sensing electrode material (exposed outside the base film) is encapsulated by a transparent encapsulation layer; preferably the sensing electrode material is embedded in the base film and diffuses and penetrates each other. The preferred sensor structure of the present application can further improve the performance.

[0014] Further preferably, the upper surface of the sensing electrode material and / or the upper surface of the base film is encapsulated by the encapsulation layer, and the encapsulation layer is preferably a transparent encapsulation layer, and the material of the transparent encapsulation layer is selected from one or more of PDMS, Ecoflex00-30, and Casterp-2577.

[0015] Further preferably, it further comprises a lead and conductive silver glue, and the lead is connected to the sensing electrode material through the conductive silver glue, and the conductive silver glue and / or the lead is encapsulated by a transparent encapsulation layer.

[0016] According to the present application, by optimizing and screening the sensor material and structure of the flexible temperature sensor, the flexible temperature sensor can be better used in different application scenarios.

[0017] In the second aspect, the present application provides a preparation method of the (embedded base type) flexible temperature sensor, which comprises:

[0018] 1) mixing nano-silver powder, liquid metal gallium and alkaline solution, passing current and centrifuging to obtain nano-silver gallium particles with silver gallium alloy shell structure;

[0019] 2) mixing the nano-silver gallium particles with a dispersant, and performing ultrasonic dispersion treatment to obtain liquid metal gallium coated silver particle ink;

[0020] 3) printing the liquid metal gallium coated silver particle ink on a printing plate by silk screen printing, after the dispersant volatilizes, spin coating a polyimide solution, and after curing, placing in water to obtain a substrate film precursor embedded with silver gallium alloy;

[0021] 4) performing microwave heating sintering treatment on the substrate film precursor embedded with silver gallium alloy to obtain a substrate film embedded with silver gallium alloy;

[0022] 5) welding a lead wire on the circular electrode of the sensing electrode material after microwave heating sintering, and then packaging. The preparation process of the flexible temperature sensor provided by the present application can prepare a flexible temperature sensor with excellent mechanical properties and stability, is convenient to prepare, and can realize large-area preparation at low cost.

[0023] Further preferably, in step 1), a current of 1-2 A is passed through the graphite electrode for 5-10 min; the centrifugation adopts differential centrifugation, and the rotation speed is 10,000-20,000 rpm; preferably, the particle size of the nano-silver powder is 20-50 nm; the alkaline solution is selected from one or more of a sodium hydroxide solution, a potassium hydroxide solution, and a calcium hydroxide solution, preferably the alkaline solution is a strong alkaline solution, and the concentration of the alkaline solution is preferably 1-5 mol / L; and the mass ratio of the nano-silver powder to the liquid metal gallium is preferably 2:1-1:9.

[0024] Further preferably, in step 2), the power of the ultrasonic dispersion treatment is 150-200 W, and the ultrasonic dispersion treatment preferably adopts cyclic ultrasonic for 10-20 times; preferably, the ultrasonic switch is set to be turned on for 2 s and turned off for 2 s for a total of 4 min, and the total ultrasonic time is 20-40 min, and water bath cooling is preferably performed between each cycle; preferably, the dispersant is selected from one or more of a PVP aqueous solution with a mass fraction of 10%-15%, a PVP n-decanol solution with a mass fraction of 3%-5%, and a PVP n-hexanol solution with a mass fraction of 3%-5%, and the mass ratio of the nano-silver gallium particles to the dispersant is 2:1-3:1. The present application mixes the nano-particles with a silver gallium shell structure and the dispersant in a specific ratio and performs the above ultrasonic dispersion treatment, so that the liquid metal gallium coated silver particle ink with uniform dispersion and better stability can be obtained.

[0025] Further preferably, in step 3), the screen printing screen plate size is preferably 200-500 mesh; the spin coating rotation speed is set to a pre-rotation speed of 300-500 rpm for 15-20 s, then the rotation speed is increased to 1500-2200 rpm for 15-20 s; the curing is performed under vacuum heating, preferably at a vacuum degree of-0.85 to-0.95 MPa and a temperature of 150-220 DEG C for 2-3 h. By optimizing the screen printing, spin coating and vacuum heating curing mode and conditions, the sensing electrode is better embedded in the base film, further improving its close combination with the base and the stability of the base film embedded with the silver-gallium alloy, so that the comprehensive performance of the flexible sensor is better.

[0026] Further preferably, in step 4), the microwave heating sintering treatment time is 1-3 s, and the sintering temperature is 70-90 DEG C. The specific microwave heating sintering method and conditions used in the present application can make the base film embedded with the liquid metal gallium coated silver nanoparticle electrode be cured more quickly, while the mechanical performance of the prepared sensor is further improved.

[0027] Further preferably, in step 5), the packaging material is selected from one or more of PDMS, Ecoflex 00-30, Casterp-2577; and the conductive silver glue is used to weld the lead wire. The use of the above transparent packaging layer and conductive silver glue helps to improve the influence of the environment on the measurement accuracy of the flexible temperature and humidity sensor.

[0028] The embedded base type flexible temperature sensor provided by the present application uses silver-gallium alloy as the sensing electrode, which has the advantages of good stability, high surface activity, can effectively reduce the energy required to excite the ink, and is better combined with the base material; the sensing electrode is almost completely embedded in the base film, the upper surface of the sensing electrode is almost flush with the surface of the base film, and the mechanical performance and measurement stability of the flexible temperature sensor are greatly enhanced; the microwave heating sintering method is used to make the base film embedded with the liquid metal gallium coated silver nanoparticle electrode be cured quickly and the performance be improved. The preparation method proposed by the present application is simple, convenient to prepare, and can realize low-cost large-area preparation. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0030] Figure 1is a structural schematic diagram of the embedded substrate type ultra-thin flexible temperature sensor provided by the present application.

[0031] Figure 2 is a cross-sectional view of the embedded substrate type ultra-thin flexible temperature sensor provided by the present application at A-A.

[0032] Figure 3 is a schematic diagram of a substrate film model embedded with a silver-gallium electrode provided by the present application.

[0033] Figure 4 is a structural size diagram of the embedded ultra-thin flexible temperature sensor provided by the present application.

[0034] Figure 5 is a microstructure diagram of the conductive silver-gallium ink printed on a glass substrate (a), after spin coating polyimide and curing separation (b), and after microwave heating sintering (c) in Example 1 of the present application.

[0035] Figure 6 is the result of 15 temperature tests of the flexible temperature and humidity sensor prepared by Example 1 in a constant temperature oven, Fig. a is the corresponding resistance diagram of 15 consecutive cycle tests, and Fig. b is the resistance response diagram at different temperatures.

[0036] Figure 7 is the curve fitting of the 15 temperature tests of the flexible temperature and humidity sensor prepared by Example 1 in a constant temperature oven.

[0037] Figure 8 is the resistance change of the flexible temperature sensor prepared by Example 1 in 15000 bending experiments.

[0038] Reference signs:

[0039] 1, silver-gallium electrode; 2, substrate film; 3, transparent packaging layer; 4, conductive silver paste; 5, lead wire; 6, embedded electrode film structure. DETAILED DESCRIPTION

[0040] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. The following embodiments are used to illustrate the present application, but not to limit the scope of the present application. If the specific technology or condition is not specified in the embodiments, it is carried out according to the technology or condition described in the literature in the art, or according to the product manual. If the reagent or instrument is not specified by the manufacturer, it is a conventional product that can be purchased through a regular channel.

[0041] The following embodiments are used to illustrate the present application, but not to limit the scope of the present application.

[0042] In the description of the present application, unless otherwise specified, the terms "upper", "lower", "inner", "outer" and the like indicate the orientation or positional relationship shown in the drawings, which are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the system or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0043] As shown in Figure 1 and Figure 2 The present application provides an embedded substrate type flexible temperature sensor. The flexible embedded substrate type flexible temperature sensor includes a silver gallium electrode 1, a substrate film 2 (PI), a transparent packaging layer 3, a conductive silver glue 4, and a lead wire 5. The embedded substrate type flexible temperature sensor is an embedded electrode thin film structure 6, the silver gallium electrode 1 is completely embedded in the substrate film 2 to form an embedded electrode thin film structure, and the four lead wires 5 are connected to the silver gallium electrode 1 through the conductive silver glue 4, and a layer of transparent packaging layer 3 is packaged thereon. As shown in Figure 3 The silver gallium electrode 1 is not only embedded in the substrate film 2 in the overall structure, but also diffuses and penetrates with the nano silver gallium particles during the curing process of the polyimide solution, so that the formed silver gallium electrode is more closely combined with the substrate film 2, greatly improving the mechanical properties and measurement stability of the flexible sensor.

[0044] The present application also provides a preparation method of the embedded substrate type flexible temperature sensor, comprising:

[0045] Step S11: Put nano silver powder and liquid gallium into a strong alkaline solution, pass 1A-2A current through the graphite electrode for 5-10 minutes, and then obtain silver gallium nano particles by differential centrifugation;

[0046] Step S12: Add the silver gallium nano particles to the dispersant, and disperse by ultrasonic until there is no obvious particle feeling, to obtain conductive silver gallium ink;

[0047] Step S13: Print the conductive silver gallium ink on the printing substrate by screen printing, and after the dispersant volatilizes, spin coat a layer of polyimide solution on the surface of the printing plate, and after curing for 2-3 hours under vacuum heating conditions, put it into deionized water to obtain a substrate film precursor with embedded silver gallium alloy;

[0048] Step S14: Put the substrate film precursor with embedded silver gallium alloy into a microwave cavity for microwave heating and sintering treatment, and obtain shell-shell sintering by microwave induction particle silver gallium shell heat effect, to obtain a substrate film with embedded silver gallium alloy electrode;

[0049] Step S15: welding the lead wire for measurement on the round electrode of the sensing electrode in the substrate film embedded with the silver-gallium alloy electrode after sintering is completed, and packaging the upper surface after welding is completed.

[0050] As shown in Figure 4 the embodiment of the present application, the diameter of the silver-gallium electrode 1 is 0.3 mm, the silver-gallium electrode 1 is in a serpentine shape and the two ends thereof are connected with the lead wire through the conductive silver glue 3, the diameter of the conductive silver glue 3 is 3 mm, and the overall structural size of the silver-gallium electrode 1 and the conductive silver glue 3 is: length 17.4 mm, width 10.84 mm.

[0051] In the embodiment of the present application, the main materials are as follows: the material used for the substrate film is polyimide solution, the transparent packaging layer is PDMS solution, and the sensing electrode is silver-gallium alloy. The processes such as ultrasonic, screen printing, microwave sintering and the like are adopted, and the preparation and test conditions in the embodiment are all under normal temperature and pressure unless otherwise specified.

[0052] The production process of the embedded substrate type flexible temperature sensor will be described in further detail below.

[0053] Embodiment 1

[0054] (1) Put the nano-silver powder (particle size 20 nm) and liquid gallium (mass ratio of nano-silver powder to liquid gallium 1:2) in a sodium hydroxide solution with a concentration of 2 mol / L, pass a current of 1 A through a graphite electrode for 10 min, and then perform differential centrifugation at 10,000 rpm to obtain silver-gallium nanoparticles.

[0055] (2) Take 200 ml of a conical flask, weigh 127.5 g of deionized water, heat and stir at 50°C, and add PVP particles with a total weight of 22.5 g in small amounts and multiple times, and stir until the solution is colorless and transparent to form a PVP aqueous solution with a mass fraction of 15%.

[0056] (3) Take 10 ml of a disposable centrifuge tube, weigh 5 g of the above-prepared silver-gallium nanoparticles and 2.5 g of the above-prepared dispersant solution into the centrifuge tube, respectively, stir with a glass rod for preliminary dispersion, and allow the dispersant to gradually penetrate to the bottom of the centrifuge tube.

[0057] (4) Perform mechanical dispersion using an ultrasonic crusher, select a 3 mm ultrasonic drill bit, set the parameters to 150 W power, set the ultrasonic switch to 2 s on and 2 s off, 4 min per cycle, a total of 15 cycles, and the total ultrasonic time is 30 min; after each cycle is completed, use cold water outside the centrifuge tube for water bath cooling.

[0058] (5) Print a size of 10 mm x 10 mm on a glass plate using a 300 mesh screen plate Figure 4The serpentine pattern is shown, and then a layer of polyimide solution is spin-coated on the glass using a spin coater, with the spin coater parameters set to a pre-rotation speed of 500 rpm for 20 s, then increased to 2200 rpm for 20 s.

[0059] (6) After spin coating, it is placed in a vacuum drying box with a vacuum degree of -0.88 MPa and a temperature of 200°C for 3h, and then placed in deionized water to form a substrate film with embedded silver-gallium alloy electrodes. The substrate film with embedded silver-gallium alloy electrodes is then placed in a microwave cavity for heating and sintering for 2s at a sintering temperature of 80°C.

[0060] (7) After the above processing is completed, two 0.1mm diameter enameled wires are welded on each of the two circular electrodes of the serpentine electrode using conductive silver paste, which is used to measure the resistance change of the sensor caused by temperature change.

[0061] (8) Finally, a layer of PDMS solution is coated on the surface using the tilt flow leveling method to prepare a transparent packaging layer, which further protects the embedded substrate type flexible temperature sensor and reduces the influence of the environment on the measurement results. Figure 5 A microstructure diagram of this embodiment, the thickness of the sensing electrode material after microwave sintering is about 7um; the overall average thickness of the substrate film is about 25um.

[0062] Example 2

[0063] (1) The nano-silver powder (particle size 20nm) and liquid gallium (mass ratio of nano-silver powder to liquid gallium 1:1) are placed in a 1mol / L sodium hydroxide solution, a 2A current is passed through the graphite electrode for 5min, and then silver-gallium nanoparticles are obtained by differential centrifugation at 10000rpm.

[0064] (2) Take 200ml conical flask, weigh 142.5g hexanol solution, heat and stir at 90°C, add a small amount of PVP particles with a total weight of 7.5g in several times, and stir the solution until it is colorless and transparent.

[0065] (3) Take 10ml disposable centrifuge tube, weigh 5g of the above prepared silver-gallium nanoparticles and 2.5g of the above prepared dispersant solution, add them into the centrifuge tube respectively, and stir with a glass rod for preliminary dispersion, so that the dispersant gradually penetrates to the bottom of the centrifuge tube.

[0066] (4) Mechanical dispersion is performed using an ultrasonic crusher, a 3mm ultrasonic drill bit is selected, the parameters are set to 200W power, the ultrasonic switch is set to 2s on and 2s off, 4min per cycle, a total of 10 cycles, the total ultrasonic time is 20min; after each cycle, water bath cooling is performed outside the centrifuge tube.

[0067] (5) Print a serpentine pattern on a glass plate with a 300 mesh silk screen with a size as shown in the figure, and then spin a layer of polyimide solution on the glass with a spin coater, with the spin coater parameters set to a pre-rotation speed of 500 rpm for 20 s, and then to 2200 rpm for 20 s. Figure 4

[0068] (6) After spin coating, place it in a vacuum drying box with a vacuum degree of -0.88 MPa and a temperature of 200°C for 3 h, and then place it in deionized water to form a substrate film with embedded silver-gallium alloy electrodes. Then, place the substrate film with embedded silver-gallium alloy electrodes in a microwave cavity and heat and sinter for 2 s at a sintering temperature of 80°C.

[0069] (7) After the above treatment is completed, use conductive silver paste to weld two enameled wires with a diameter of 0.1 mm on each of the two circular electrodes of the serpentine electrode for measuring the resistance change of the sensor caused by temperature change.

[0070] (8) Finally, use a tilt flow method to cover the surface with a layer of Ecoflex 00-30 solution to prepare a transparent encapsulation layer to further protect the embedded substrate-type flexible temperature sensor and reduce the influence of the environment on its measurement results.

[0071] Comparative Example

[0072] (1) Put nano-silver powder (particle size 20 nm) and liquid gallium (mass ratio of nano-silver powder to liquid gallium 1:2) in a 2 mol / L sodium hydroxide solution, pass a 1A current through a graphite electrode for 10 min, and then perform differential centrifugation at 10,000 rpm to obtain silver-gallium nanoparticles.

[0073] (2) Take 200 ml of a conical flask, weigh 127.5 g of deionized water, heat and stir at 50°C, and add a total of 22.5 g of PVP particles in small amounts and multiple times, and stir until the solution is colorless and transparent to form a 15% PVP aqueous solution.

[0074] (3) Take 10 ml of a disposable centrifuge tube, weigh 5 g of the above-prepared silver-gallium nanoparticles and 2.5 g of the above-prepared dispersant solution into the centrifuge tube, and stir with a glass rod to perform preliminary dispersion, allowing the dispersant to gradually penetrate to the bottom of the centrifuge tube.

[0075] (4) Perform mechanical dispersion using an ultrasonic crusher, select a 3 mm ultrasonic drill bit, set the parameters to 150 W power, and set the ultrasonic switch to 2 s on and 2 s off, 4 min per cycle, a total of 15 cycles, and a total ultrasonic time of 30 min; after each cycle, use cold water outside the centrifuge tube for water bath cooling.

[0076] ​(5) Spin a layer of polyimide solution on the glass using a spin coater, the spin coater parameters are set as pre-rotation speed 500 rpm, spin for 20 s, then increase to 2500 rpm, spin for 20 s. After spin coating, it is placed in a vacuum drying oven with a vacuum degree of -0.88 MPa and a temperature of 200°C for 3 h, and then placed in deionized water to form a base film.

[0077] (6) Print a serpentine pattern with a size as shown in the figure on the glass plate using a 300-mesh screen, and then sinter it using a traditional low-temperature heating method. That is, use a 250°C heating table to sinter in an air atmosphere for 24 hours Figure 4

[0078] (7) After the above treatment, use conductive silver paste to weld two enameled wires with a diameter of 0.1 mm on each of the two circular electrodes of the serpentine electrode, which are used to measure the resistance change of the sensor caused by temperature change.

[0079] (8) Finally, use a tilt flow leveling method to cover the surface with a layer of PDMS solution to prepare a transparent packaging layer to further protect the embedded base-type flexible temperature sensor and reduce the influence of the environment on the measurement results. The flexible sensor prepared in this way is prone to breakage and peeling of the sensing electrode and the base film under bending conditions, greatly reducing the service life. And the printing process on the glass substrate is easier to implement than on the base film. In this comparative example, a slightly higher spin speed is used than in Example 1 to prepare a thinner base, but the thinner base prepared at a spin speed outside the preferred range exhibits greater brittleness than flexibility during the sintering process, resulting in some degree of breakage of the base.

[0080] Experimental Example 1

[0081] The flexible temperature sensor obtained in Example 1 was subjected to a cycle test. The entire temperature sensor was placed flat in a programmable constant temperature and humidity test chamber, and the four sides were fixed with adhesive tape. The four leads were connected to a Keysight 34420A benchtop digital multimeter, and the digital multimeter was connected to a computer, so that the data changes could be recorded in real time on the computer.

[0082] The temperature range produced by the test chamber setting program was -10-50°C, the test data frequency was 1 per minute, and the temperature change duration in the program was set to 30 min. After reaching the set temperature, the temperature was maintained for 60 min. We selected the data of the last 30 min of the stable period at each temperature as the sample (n=30), and took the average value as the resistance value at this temperature in this cycle. The experimental results are shown in Figure 6 Figure 7 The results show that the flexible temperature sensor prepared using the present application has good measurement accuracy, repeatability and linearity.​​

[0083] In order to test the fatigue durability of the embedded electrode, the temperature and humidity sensor obtained in Example 1 was subjected to a bending test. The test angle was 180°, and a total of 15000 cycles of bending were performed, and the resistance change was measured by a four-wire method. The experimental results are shown in Figure 8 It was found that the resistance of the sample showed a process of slightly increasing first, then approaching stable, and then gradually decreasing. This phenomenon occurred because during the rapid bending, the internal particles of the sensing electrode rubbed against each other, causing the temperature to rise, resulting in a slight increase in resistance. After 15000 bending cycles, the temperature gradually decreased, and the resistance returned to the initial state. During the bending test, the actual resistance change was only in the range of 306-308 mΩ, showing good mechanical properties and test stability.

[0084] Although the present application has been described in detail with general description and specific embodiments above, some modifications or improvements can be made on the basis of the present application, which is obvious to those skilled in the art. Therefore, these modifications or improvements made on the basis of not deviating from the spirit of the present application, are within the scope of the present application claimed.

Claims

1. A method of preparing a flexible temperature sensor, characterized by, The method comprises the following steps: 1) mixing nano-silver powder, liquid metal gallium and an alkaline solution, passing an electric current, centrifuging to obtain nano-silver gallium particles; 2) mixing the nano-silver gallium particles with a dispersing agent, and performing ultrasonic dispersion treatment to obtain silver particle ink coated with liquid metal gallium; 3) printing the silver particle ink coated with liquid metal gallium on a printing plate by silk screen printing, volatilizing the dispersing agent, spin-coating a polyimide solution, and placing the solution in water after solidification to obtain a substrate film precursor embedded with silver gallium alloy; 4) performing microwave heating and sintering treatment on the substrate film precursor embedded with silver gallium alloy to obtain a substrate film embedded with silver gallium alloy; 5) welding a lead wire on the circular electrode of the sensing electrode material after microwave heating and sintering, and then performing packaging. The flexible temperature sensor comprises a substrate film, a sensing electrode material embedded in the substrate film, and a packaging layer; and the sensing electrode material is silver gallium alloy.

2. The method of claim 1, wherein the flexible temperature sensor is prepared by the steps of: The sensing electrode material is a silver electrode coated with liquid metal gallium, and the thickness of the sensing electrode material is 5-10 um.

3. The method of claim 2, wherein the flexible temperature sensor is prepared by the steps of: The sensing electrode material is a silver electrode coated with liquid metal gallium, and the thickness of the sensing electrode material is 7-10 um.

4. The method of claim 1, wherein the flexible temperature sensor is prepared by a process comprising: The substrate film is a polyimide film, and the thickness of the substrate film is not greater than 40 um.

5. The method of claim 4, wherein the flexible temperature sensor is prepared by the steps of: The thickness of the substrate film is 23-40 um.

6. The method of claim 5, wherein the flexible temperature sensor is prepared by the steps of: The thickness of the substrate film is 25-40 um.

7. The method of claim 2, wherein the flexible temperature sensor is prepared by the steps of: The sensing electrode material is embedded in the substrate film, and the surface of the sensing electrode material is flush with the surface of the substrate film.

8. The method of claim 7, wherein the flexible temperature sensor is prepared by the steps of: The surface of the sensing electrode material is exposed outside the substrate film.

9. The method of claim 1, wherein the flexible temperature sensor is prepared by a process comprising: The flexible temperature sensor further comprises a lead wire and conductive silver glue, and the lead wire is connected to the sensing electrode material through the conductive silver glue.

10. The method of claim 9, wherein the flexible temperature sensor is prepared by the steps of: The conductive silver glue and the lead wire are packaged by using a transparent packaging layer.

11. The method of claim 10, wherein the flexible temperature sensor is prepared by the steps of: The surface part of the sensing electrode material exposed outside the substrate film is packaged by using a transparent packaging layer.

12. The method of claim 1, wherein the flexible temperature sensor is prepared by a process comprising: In step 1), an electric current of 1-2 A is passed through a graphite electrode for 5-10 min; and the centrifugation is performed by differential centrifugation at a speed of 10,000-20,000 rpm.

13. The method of claim 12, wherein the flexible temperature sensor is prepared by a process comprising: The particle size of the nano-silver powder is 20-30 nm; and the alkaline solution is selected from one or more of a sodium hydroxide solution, a potassium hydroxide solution and a calcium hydroxide solution.

14. The method of claim 13, wherein the flexible temperature sensor is prepared by a process comprising: The alkaline solution is a strong alkaline solution, and the concentration of the alkaline solution is 1-5 mol / L.

15. The method of claim 1, wherein the flexible temperature sensor is prepared by a process comprising: In step 2), the power of the ultrasonic dispersion treatment is 150-200 W, and the ultrasonic dispersion treatment is performed by cyclic ultrasonic for 10-20 times.

16. The method of claim 15, wherein the flexible temperature sensor is prepared by the steps of: In step 2), the ultrasonic switch is set to be turned on for 2 s and turned off for 2 s for a total of 4 min, and the total ultrasonic time is 20-40 min, and water bath cooling is performed between each cycle.

17. The method of claim 16, wherein the flexible temperature sensor is prepared by, In step 2), the dispersing agent is selected from one or more of a PVP aqueous solution with a mass fraction of 10%-15%, a PVP n-pentanol solution with a mass fraction of 3%-5% and a PVP n-hexanol solution with a mass fraction of 3%-5%, and the mass ratio of the nano-silver gallium particles to the dispersing agent is 2:1-3:

1.

18. The method of claim 1, wherein the flexible temperature sensor is prepared by a process comprising: In step 3), the screen printing screen plate size is 200-500 mesh; the spin coating rotation speed is set to pre-rotation speed of 300-500 rpm, rotating for 15-20 s, then the rotation speed is increased to 1500-2200 rpm, rotating for 15-20 s.

19. The method of claim 18, wherein the flexible temperature sensor is prepared by, In step 3), the curing is carried out under vacuum heating conditions, the vacuum degree is -0.85 to -0.95 MPa, the temperature is 150-220 ℃, and the curing time is 2-3 h.

20. The method of claim 1, wherein the flexible temperature sensor is prepared by a process comprising: In step 4), the microwave heating treatment time is 1-3 s, and the sintering temperature is 70-90 ℃.

21. The method of claim 1-20, wherein the flexible temperature sensor is prepared by, In step 5), the encapsulating material is selected from one or more of PDMS, Ecoflex 00-30, and Casterp-2577.

22. The method of claim 21, wherein the flexible temperature sensor is prepared by, In step 5), the encapsulating material is welded with a conductive silver glue wire.

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