Preparation method and application of graphene high-barrier flexible temperature sensor

Abstract

The present invention discloses a method for preparing a graphene high-barrier flexible temperature sensor. The quality of the graphene film grown by chemical vapor deposition is much higher than that of ordinary graphene. Due to the strong π-π interaction between PEDOT:PSS and the graphene film, the graphene film can be tightly connected to the PEDOT:PSS layer. Since there are graphene films on both sides, a sandwich structure of thermoplastic polyimide-graphene-PEDOT:PSS-graphene-thermoplastic polyimide is formed. By utilizing the high barrier property of the graphene film, the barrier capacity of the entire sensor can be greatly improved, and the service life of the sensor can be greatly increased. The graphene film can be tightly connected to the PEDOT:PSS layer, which can improve its stability.

Description

Technical Field

[0001] The present invention relates to the technical field of temperature sensor preparation, and in particular to a preparation method and application of a graphene high-barrier flexible temperature sensor. Background Art

[0002] Currently, the thermoelectric materials for wearable flexible temperature sensors mainly fall into the following categories: 1. Carbon-containing materials. Common carbon materials include carbon black, graphite, carbon nanotubes, and graphene. 2. Materials containing metals and their oxides. Common conductive metal materials include gold, silver, copper, platinum, nickel, and aluminum. 3. Materials containing conductive polymers. Commonly used thermosensitive polymer materials include PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid)), P3HT (poly-3-hexylthiophene), pNIPAM (poly(N-isopropylacrylamide)), PPy (polypyrrole), PVDF (polyvinylidene fluoride), etc. Generally, effective temperature-sensitive conductive materials are prepared by two methods: preparing a single thermoelectric material and preparing a composite material by mixing two different thermoelectric materials. Fabricating temperature-sensitive conductive materials from a single thermoelectric material: Srinivas Gandla et al. fabricated a stable and highly linear temperature sensor using laser-induced carbonization of a polyimide (PI) substrate. This sensor exhibited a response time of 1 s, a resolution of 0.2°C, and a temperature coefficient of resistance (TCR) of 0.00142°C⁻¹. Zheng Cui et al. reported a kirigami-inspired, breathable and stretchable temperature sensor based on silver nanowires (AgNWS). The percolation network of AgNWs was encapsulated in a thin polyimide film. The TCR of the AgNW network was tailored by varying the nanowire density and thermal annealing temperature. A temperature sensor fabricated with an AgNW network annealed at 200°C and a density of 2.053 μm⁻¹ was demonstrated, achieving a TCR of 3.32 × 10⁻³°C⁻¹ and a sensitivity of 0.47 Ω / °C. PEDOT:PSS is a new organic conductive polymer commonly used in printable, flexible temperature sensors. Yu et al. fabricated a flexible temperature sensor with microcracks using pre-stretched and acid-treated PEDOT:PSS and PDMS (polydimethylsiloxane). Higher crack density and larger crack length resulted in greater temperature sensitivity. The sensor with the optimal crack morphology (crack length: 185.2 μm, crack density: 22.84 mm⁻¹) exhibited a high-temperature sensitivity of 0.042°C⁻¹ and good linearity of 0.998. A thermosensitive conductive material can be prepared by blending two or more thermosensitive materials: Ju et al. fabricated a highly sensitive resistive temperature sensor composed of a thermosensitive poly(n-isopropylacrylamide) (pNIPAM) hydrogel, PEDOT:PSS, and CNTs. The device exhibited a sensitivity of 2.6%°C⁻¹ within the temperature range of 25–40°C and could accurately detect skin temperature changes of 0.5°C. However, these temperature sensors still have the following drawbacks: 1. They have weak barrier properties, failing to block small molecules such as oxygen, carbon dioxide, and water vapor, which means the sensor's service life needs to be improved. 2. Temperature sensors fabricated from temperature-sensitive conductive materials made from a single thermoelectric material have some good properties, but others suffer from other performance deficiencies.3. Temperature sensors made using pre-stretching methods are susceptible to interference from non-temperature factors such as stress and tension, which can affect the accuracy of measurement results. When mixing two or more thermosensitive materials to make a temperature-sensitive conductive material, it is necessary to consider the interaction between the different materials and the effect of the material ratio on temperature sensing.

[0003] To this end, a preparation method and application of a graphene high-barrier flexible temperature sensor are provided. Summary of the Invention

[0004] The object of the present invention is to provide a method for preparing a graphene high-barrier flexible temperature sensor to solve the above-mentioned problems.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for preparing a graphene high-barrier flexible temperature sensor, characterized in that it comprises the following steps:

[0006] a. Growing graphene on a metal substrate using chemical vapor deposition to obtain a first sample;

[0007] b. Spin-coating a flexible substrate solution onto the graphene of the first sample, and heating and curing the flexible substrate solution to obtain a second sample, wherein the second sample is now arranged with a flexible substrate, graphene, and a metal substrate in order from top to bottom; the flexible substrate solution in step b is a thermoplastic polyimide solution or a thermosetting polyimide solution;

[0008] c. placing the second sample into a plasma bombardment device with the metal substrate facing upward, evacuating the sample and bombarding the plasma, and obtaining a third sample after the bombardment is completed;

[0009] d. Attach one side of the flexible substrate of the third sample to a hard board, place the entire piece with the hard board facing upward into the etching solution, secure it so it is suspended in the solution, etch away the metal substrate, and then clean it to obtain the fourth sample;

[0010] e. The fourth sample was placed with the hard board side facing down, and a PEDOT:PSS solution was spin-coated on top of the graphene. The solution was vacuum dried and solidified to obtain a fifth sample. The fifth sample obtained was a PEDOT:PSS film, graphene, and a flexible substrate arranged in that order. The PEDOT:PSS spin-coating speed was 1000-5000 rpm, and the time was 5-60 s.

[0011] f. Using the fifth sample, a copper wire is fixed to a PEDOT:PSS film using a conductive silver paste as an electrode to obtain a sixth sample; wherein the PEDOT:PSS film is connected to the copper wire via the conductive silver paste;

[0012] g. Repeat steps a, b, and c to obtain the seventh sample;

[0013] h. Place the seventh sample with the flexible substrate facing upward into an etching solution, etch away the metal substrate, and then clean the sample to obtain an eighth sample. The eighth sample has the graphene and the flexible substrate arranged from top to bottom.

[0014] i. Use the side of the sixth sample with the PEDOT:PSS film facing up to fish out the eighth sample, vacuum dry it, and separate the hard plate to obtain the final sensor product. The sensor is the eighth sample placed on top of the sixth sample, that is, the flexible substrate, graphene, PEDOT:PSS film, graphene, and flexible substrate are arranged in order.

[0015] Furthermore, the etching solution in step d and step h is ammonium persulfate or ferric chloride with a concentration of 0.1-3 mol / L; etching in step d and step h is performed twice, the first etching time is 1-3 hours, and the second etching time is 1-20 hours.

[0016] Furthermore, the spin coating speed in step b is 100-2000 rpm, and the time is 5-60 s.

[0017] Furthermore, the vacuuming time in step c is 5-30 minutes.

[0018] Furthermore, the power of the bombardment plasma in step c is low, the power of the low gear is 7.16W, and the bombardment time is 10-60min.

[0019] Furthermore, the metal substrate in step a is one of copper, nickel, platinum, cobalt, iron, molybdenum, ruthenium or iridium.

[0020] Furthermore, the hard plate in step d is a quartz plate.

[0021] Furthermore, the specific operation of the cleaning step in step d is: first wash once with ultrapure water, then wash once with a solution of hydrochloric acid, hydrogen peroxide and water in a ratio of 1:1:20 for 5-60 minutes, and then wash three times with ultrapure water for 1-30 minutes each time.

[0022] Furthermore, in step b, the heating and curing temperature is 60-90° C. and the time is 10-60 minutes.

[0023] Furthermore, the flexible temperature sensor obtained according to the preparation method is used in wearable device sensors.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The quality of graphene films grown by chemical vapor deposition is much higher than that of ordinary graphene. Due to the strong π-π interaction between PEDOT:PSS and the graphene film, the graphene film can be tightly connected to the PEDOT:PSS layer. With graphene films on both sides, a sandwich structure of thermoplastic polyimide-graphene-PEDOT:PSS-graphene-thermoplastic polyimide is formed. The high barrier properties of the graphene film can greatly improve the barrier ability of the entire sensor to small molecules such as oxygen, carbon dioxide, and water vapor. The barrier performance is extremely excellent and can significantly increase its service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A schematic structural diagram of an embodiment of the present invention;

[0027] In the figure: 1-eighth sample, 2-sixth sample, 3-graphene, 4-flexible substrate, 21-PEDOT:PSS film, 22-copper wire, 23-conductive silver paste. DETAILED DESCRIPTION

[0028] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0029] See also Figure 1 The present invention provides a technical solution: a method for preparing a graphene high-barrier flexible temperature sensor, characterized in that it comprises the following steps:

[0030] a. Growing graphene on a metal substrate using chemical vapor deposition to obtain a first sample; the graphene in step a is single-layer graphene, double-layer graphene, or multi-layer graphene; the first sample comprises a metal substrate and graphene grown on the metal substrate; graphene can also be grown on the metal substrate by coating a slurry and then drying the slurry;

[0031] Preferably, the graphene in step a is single-layer graphene.

[0032] b. Spin-coating the flexible substrate solution onto the graphene of the first sample, and heating and curing the flexible substrate solution to obtain a second sample, wherein the second sample is now a flexible substrate, graphene, and a metal substrate arranged in sequence from top to bottom; the flexible substrate solution in step b is a thermoplastic polyimide solution or a thermosetting polyimide solution, and the spin-coating speed is 100-2000 rpm for 5-60 s; the temperature for heating and curing the thermoplastic polyimide solution or the thermosetting polyimide solution is 60-90° C. for 10-60 min; it should be noted that during growth, the side of the metal substrate on which the carbon source is mainly in contact with and on which graphene is grown is the front side, and the other side is the back side; the second sample is now a first flexible substrate solution, a first graphene, and a first metal substrate arranged in sequence from top to bottom; the spin-coating machine can be a uniform glue spin coater, such as the WS-650Mz-23NPP of the brand LAURELL, and the heating device can be a heating table or a blast drying oven or a vacuum drying oven;

[0033] c. placing the second sample into a plasma bombardment device, wherein the metal substrate in the second sample faces upward, and bombarding the plasma after vacuuming, and completing the bombardment to obtain a third sample; the vacuuming time in step c is 5-30 min; the power of the plasma bombardment is low gear, the power of the low gear is 7.16 W, and the bombardment time is 10-60 min; it should be noted that the name of the instrument used for bombarding the plasma is Harrick PDC-002 plasma cleaning machine, which is a general instrument, and the low gear parameters are 716 VDC, 10 mA DC, and 7.16 W. The bombardment plasma is successful when partial copper oxide appears on the back; the vacuuming device is also a plasma bombardment device; that is, the metal substrate, graphene, and flexible substrate in the second sample are placed in the plasma bombardment device from top to bottom and bombarded;

[0034] d. Adhere one side of the flexible substrate in the third sample to a hard plate, place the entire sample with the hard plate facing upward in an etching solution, fix it so that it is suspended in the solution, etch away the metal substrate, and then wash it to obtain a fourth sample; the etching solution in step d is ammonium persulfate or ferric chloride, with a concentration of 0.1-3 mol / L; it should be noted that the hard plate can be a quartz plate or a hard plate that does not react with the flexible substrate (thermoplastic polyimide or thermosetting polyimide, etc.), and the entire sample is arranged from top to bottom in sequence. Then, the entire sample is placed in the etching solution with the hard plate facing upward, and the bottom metal substrate is allowed to contact the etching solution; the fourth sample obtained now contains graphene and a flexible substrate, but no metal substrate. At this time, the entire sample is arranged from top to bottom in sequence.

[0035] e. The fourth sample is placed with the hard board side facing down, and a PEDOT:PSS solution is spin-coated on the graphene. The solution is vacuum dried and solidified to obtain a fifth sample, wherein the fifth sample is a PEDOT:PSS film, graphene, and a flexible substrate arranged in this order. The PEDOT:PSS spin coating speed is 1000-5000 rpm, and the time is 5-60 s. It should be noted that the spin coating machine can be a spin coater, and the PEDOT:PSS solution is spin-coated on the graphene. After vacuum drying and solidification, the PEDOT:PSS solution becomes a PEDOT:PSS film.

[0036] f. Using the fifth sample, a copper wire is fixed to the PEDOT:PSS film using conductive silver paste as an electrode to obtain a sixth sample. In this case, the sixth sample comprises a PEDOT:PSS film, graphene, and a flexible substrate arranged in order from top to bottom, wherein the PEDOT:PSS film is connected to the copper wire via the conductive silver paste.

[0037] g. Repeat steps a, b, and c to obtain the seventh sample. The seventh sample is used to cover and seal the entire sixth sample. The seventh sample is the same as the second sample.

[0038] h. placing the seventh sample with the flexible substrate facing upward into an etching solution, etching away the metal substrate, and then washing to obtain an eighth sample, wherein the graphene and the flexible substrate are arranged from top to bottom in the eighth sample; that is, the flexible substrate, the graphene, and the metal substrate are arranged from top to bottom and placed into the etching solution, with the metal substrate contacting the etching solution; the resulting eighth sample is the graphene and the flexible substrate arranged from top to bottom;

[0039] i. Remove the eighth sample from the sixth sample with the PEDOT:PSS film facing upward. After vacuum drying, separate the quartz plate to obtain the final sensor product. The sensor is the eighth sample placed on top of the sixth sample. Specifically, the flexible substrate 4, graphene 3, PEDOT:PSS film 21, graphene 3, and flexible substrate 4 are arranged in this order. The structure is a sandwich of thermoplastic polyimide-graphene-PEDOT:PSS-graphene-thermoplastic polyimide. Copper wire 22 is connected to the PEDOT:PSS film via conductive silver paste 23. Copper wire 22 is located above the conductive silver paste 23. Multiple copper wires are permitted. Figure 1 Only one wire is drawn in the figure. The copper wire can also be made of other conductive metal wires. The conductive silver paste can be fixed with other materials such as conductive paint. Figure 1 This is a structural schematic diagram of the final temperature sensor of the present application. The temperature sensor of the present application includes a flexible substrate 4, graphene 3, a PEDOT:PSS film 21, graphene 3, and a flexible substrate 4 arranged in sequence, and a copper wire 22 is connected between the graphene 3 and the PEDOT:PSS film 21 through a conductive silver paste 23.

[0040] The spin coating speed in step b is 100-2000 rpm and the time is 5-60 s. The spin coating is performed by a LAURELL spin coater, model WS-650Mz-23NPP.

[0041] Wherein, in the above-mentioned graphene transfer method based on thermoplastic polyimide sacrificial layer, the metal substrate in step a is one of copper, nickel, platinum, cobalt, iron, molybdenum, ruthenium or iridium.

[0042] Furthermore, the metal substrate in step a is one of copper, nickel, platinum, cobalt, iron, molybdenum, ruthenium or iridium. Preferably, the metal substrate in step a is copper.

[0043] Furthermore, the graphene in step a is single-layer graphene, double-layer graphene or multi-layer graphene. Preferably, the graphene in step a is single-layer graphene.

[0044] Furthermore, the flexible substrate solution in step b is a thermoplastic polyimide solution or a thermosetting polyimide solution. Preferably, the flexible substrate solution in step b is a thermoplastic polyimide.

[0045] Among them, in the above-mentioned preparation method and application of a graphene high-barrier flexible temperature sensor, the spin coating speed in step b is 100-2000 rpm and the time is 5-60 s.

[0046] Preferably, in the above-mentioned preparation method and application of a graphene high-barrier flexible temperature sensor, the spin coating speed of the heating and curing flexible substrate in step b is 500 rpm and the time is 10 s.

[0047] Among them, in the above-mentioned preparation method of a graphene high-barrier flexible temperature sensor and its application, the temperature of heating and curing the thermoplastic polyimide solution in step b is 60-90°C and the time is 10-60 minutes.

[0048] Preferably, in the above-mentioned preparation method of a graphene high-barrier flexible temperature sensor and its application, the temperature of heating and curing the flexible substrate in step b is 90° C. and the time is 15 minutes.

[0049] In the above-mentioned method for preparing a graphene high-barrier flexible temperature sensor and its application, the vacuuming time in step c is 5-30 minutes, preferably 20 minutes.

[0050] In the above-mentioned method for preparing a graphene high-barrier flexible temperature sensor and its application, the power of the bombarding plasma in step c is low, the power of the low gear is 7.16W, and the bombardment time is 10-60 minutes, preferably 25 minutes.

[0051] In the above-mentioned method for preparing a graphene high-barrier flexible temperature sensor and its application, the etching solution in step d is ammonium persulfate or ferric chloride, with a concentration of 0.1-3 mol / L. Preferably, it is 1 mol / L. In step h, the etching solution is also ammonium persulfate or ferric chloride, with a concentration of 0.1-3 mol / L.

[0052] The etching is divided into two times. The first etching time is 1-3 hours, preferably 3 hours. The second etching is to transfer the fourth sample into a new etching solution. The etching time is 1-20 hours, preferably 18 hours.

[0053] In the above-mentioned method for preparing a graphene-based high-barrier flexible temperature sensor and its application, the specific operation of the cleaning step (d) is as follows: first, rinse once with ultrapure water, then rinse once with a 1:1:20 solution of hydrochloric acid, hydrogen peroxide, and water for 5-60 minutes, and finally rinse three times with ultrapure water, each for 1-30 minutes. Preferably, the 1:1:20 solution of hydrochloric acid, hydrogen peroxide, and water is rinsed for 15 minutes, and the ultrapure water rinse is rinsed for 3 minutes.

[0054] Among them, in the above-mentioned preparation method and application of a graphene high-barrier flexible temperature sensor, the PEDOT:PSS spin coating speed in step e is 1000-5000 rpm, and the time is 5-60 s.

[0055] Preferably, in the above-mentioned preparation method of a graphene high-barrier flexible temperature sensor and its application, the PEDOT:PSS spin coating speed in step e is 3000 rpm and the time is 10 s.

[0056] Furthermore, the flexible temperature sensor obtained according to the preparation method is used in wearable device sensors.

[0057] Implementation Case 1

[0058] A method for preparing a graphene high-barrier flexible temperature sensor comprises the following steps:

[0059] (1) Graphene was grown on copper foil using chemical vapor deposition to obtain the first sample;

[0060] (2) Spin-coat thermoplastic polyimide onto the front side of the first sample (i.e., the graphene side) at a spin-coating speed of 500 rpm for 10 seconds. Heat-curing the thermoplastic polyimide at 90°C for 15 minutes to obtain the second sample.

[0061] (3) Place the back side of the second sample (i.e., the side with the metal substrate facing upward) into the plasma bombardment device, evacuate for 20 minutes, and then bombard the plasma at low speed for 25 minutes. After the bombardment is completed, the third sample is obtained.

[0062] (4) Glue the front of the third sample to the quartz plate, and place the entire quartz plate facing up in a 1 mol / L ammonium persulfate solution, fix it and let it suspend in the solution. Etch twice. The first etching time is 3 hours. The second etching is to transfer the third sample to a new etching solution for 18 hours. After etching away the copper foil, wash it once with ultrapure water, then wash it once with a 1:1:20 hydrochloric acid, hydrogen peroxide, and water solution for 15 minutes, and then wash it three times with ultrapure water, each time for 3 minutes. After washing, the fourth sample is obtained;

[0063] (5) With the quartz plate side facing downward, spin-coat the PEDOT:PSS solution on top of the graphene. The PEDOT:PSS spin-coating speed is 3000 rpm for 10 seconds. Then, vacuum dry and solidify to obtain the fifth sample.

[0064] (6) Using conductive silver paste, the copper wire of the fifth sample was fixed on the PEDOT:PSS film as an electrode to obtain the sixth sample;

[0065] (7) Repeat (1), (2), and (3) to obtain the seventh sample;

[0066] (8) Place the front side of the seventh sample (the side with the flexible substrate facing up) in a 1 mol / L ammonium persulfate solution. Etch the sample twice. The first etching time is 3 hours. The second etching time is 18 hours. After etching away the copper foil, wash it once with ultrapure water, then wash it once with a solution of hydrochloric acid, hydrogen peroxide, and water in a ratio of 1:1:20 for 15 minutes. Finally, wash it three times with ultrapure water for 3 minutes each time to obtain the eighth sample.

[0067] (9) Use the upward side of the sixth sample PEDOT:PSS to fish out the eighth sample, vacuum dry it, and separate the sensor from the quartz plate to obtain the final product sensor, the flexible temperature sensor.

[0068] Implementation Case 2 and Implementation Case 3 are existing methods. Table 1 shows the data obtained by measuring the products of Implementation Case 1, Implementation Case 2 and Implementation Case 3 using conventional test methods.

[0069] Implementation Case 2

[0070] A method for preparing a conventional graphene flexible temperature sensor comprises the following steps:

[0071] Add the PEDOT:PSS aqueous solution to graphene powder to prepare a 40% PEDOT:PSS / graphene solution, then stir and disperse the mixture, then sonicate at 800W for 30 minutes to obtain a PEDOT:PSS / graphene composite solution.

[0072] Thermosetting polyimide was evenly spin-coated onto a silicon wafer that had been evenly sprayed with release agent. The spin-coating process was performed at a speed of 500 rpm for 10 seconds. After spin-coating, the thermosetting polyimide was heat-cured at 90°C for 15 minutes to obtain the first sample.

[0073] The first sample was spin-coated with a PEDOT:PSS / graphene mixed solution on the thermosetting polyimide side at a speed of 3000 rpm for 10 seconds. The solution was then vacuum-dried and cured to obtain the second sample.

[0074] The second sample was made by fixing copper wire on the PEDOT:PSS film using conductive silver paste as an electrode to obtain the third sample;

[0075] The third sample, containing the flexible sensor, was spin-coated with thermosetting polyimide for encapsulation at a speed of 500 rpm for 10 seconds. After spin coating, the sample was heated and cured at 90°C for 15 minutes. The final product was encapsulated.

[0076] Implementation Case 3

[0077] A conventional method for preparing a flexible temperature sensor includes the following steps:

[0078] (1) Thermosetting polyimide is evenly spin-coated on the silicon wafer evenly sprayed with release agent. The spin-coating process is performed at a speed of 500 rpm and for 10 seconds. After the spin-coating is completed, the heat curing temperature is set at 90°C for 15 minutes. After the heat curing of the thermosetting polyimide is completed, the first sample is obtained;

[0079] (2) Spin-coat a 40% PEDOT:PS solution onto the thermosetting polyimide side of the first sample at a speed of 3000 rpm for 10 seconds. Then vacuum dry and solidify to obtain the second sample.

[0080] (3) The second sample was made by fixing the copper wire on the PEDOT:PSS film with conductive silver paste as an electrode to obtain the third sample;

[0081] (4) The third sample containing the flexible sensor was spin-coated with thermosetting polyimide for encapsulation. The spin-coating process was performed at a speed of 500 rpm for 10 seconds. After the spin-coating process was completed, the sample was heated and cured at a temperature of 90°C for 15 minutes. After encapsulation, the finished product was obtained.

[0082] The finished products of the three embodiments were tested, and the data results are shown in Table 1 below.

[0083] Example 1 Example 2 Example 3 Conductivity σ (x10-4, S / m) 3.68 2.85 1.42 Temperature coefficient of resistance TCR ( / ℃) -0.0090 -0.0073 -0.0056 Linearity change rate after 16 resistance-temperature tests (%) -0.12 -0.46 -1.09

[0084] Table 1 is a comparison chart of the effects of Examples 1-3;

[0085] Among them, the conductivity σ is measured by using the ST263 dual-electricity digital four-probe tester;

[0086] The temperature coefficient of resistance (TCR) is calculated as TCR = (R2 - R1) / (R1 * (T2 - T1)), where TCR is the temperature coefficient of resistance, and R1 and R2 are the resistance values ​​at temperatures T1 and T2 (in degrees Celsius), respectively. Set a digital multimeter to resistance measurement mode and connect the thermistor to the multimeter. Set the temperature of a thermostat or water bath to an initial temperature (e.g., 25°C) and wait for it to stabilize. After the thermostat stabilizes, record the thermistor's resistance as the initial resistance. Gradually increase the temperature of the thermostat by a certain amount (e.g., 5°C). After the thermostat stabilizes, record the corresponding temperature and thermistor's resistance. Repeat these steps to measure the resistance at 16 different temperatures. Based on the measured temperature and resistance data, calculate the temperature coefficient using the temperature coefficient definition formula. TCR = (R2 - R1) / (R1 * (T2 - T1)), where TCR is the temperature coefficient of resistance, and R1 and R2 are the resistance values ​​at temperatures T1 and T2 (in degrees Celsius), respectively. The temperature range can be 25°C, 26°C, 27°C, 39°C, and 40°C.

[0087] The linearity change rate (%) after 16 resistance-temperature tests is calculated as follows: Change rate = ((Resistance temperature coefficient calculated in the first test - Resistance temperature coefficient calculated in the 16th test) / Resistance temperature coefficient calculated in the first test) * 100%. The present invention is the first to use a sandwich structure of thermoplastic polyimide-graphene film-PEDOT:PSS-graphene film-thermoplastic polyimide to make a temperature sensor. Combined with the effect comparison chart of the embodiment in Table 1, the high barrier properties of the graphene film can greatly improve the barrier ability of the entire sensor to small molecules such as oxygen, carbon dioxide, and water vapor. The barrier performance is extremely excellent and can greatly increase its service life. When the sensor designed by this patent is working, the strong π-π interaction between PEDOT:PSS and the graphene film promotes the transport and The potential accumulates, causing a large change in the resistance of the entire material, achieving rapid conversion of thermoelectric signals, and thus realizing real-time monitoring of temperature, which can greatly improve its sensitivity, response speed and recovery time. The quality of graphene films grown by chemical vapor deposition is much higher than that of graphene produced by the redox method. Its single-layer rate, resistance and other aspects have been greatly improved, which can improve the conductive performance. In addition, due to the strong π-π interaction between PEDOT:PSS and graphene film, the graphene film can be tightly connected to the PEDOT:PSS layer, which can improve its stability.

[0088] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a graphene high-barrier flexible temperature sensor, characterized in that: The following steps are involved: a. Growing graphene on a metal substrate using chemical vapor deposition to obtain a first sample; b. Spin-coating a flexible substrate solution onto the graphene of the first sample, and heating and curing the flexible substrate solution to obtain a second sample, wherein the second sample is now arranged with a flexible substrate, graphene, and a metal substrate in order from top to bottom; the flexible substrate solution in step b is a thermoplastic polyimide solution or a thermosetting polyimide solution; c. placing the second sample into a plasma bombardment device with the metal substrate facing upward, evacuating the sample and bombarding the plasma, and obtaining a third sample after the bombardment is completed; d. Attach one side of the flexible substrate in the third sample to a hard board, place the entire sample with the hard board facing upward in an etching solution, secure it so it is suspended in the solution, etch away the metal substrate, and then clean it to obtain a fourth sample; the entire sample is arranged from top to bottom in the order of the hard board, flexible substrate, graphene, and metal substrate, and then the entire sample is placed in the etching solution with the hard board facing upward, with the bottom metal substrate in contact with the etching solution; the resulting fourth sample now contains graphene and a flexible substrate; e. The fourth sample was placed with the hard board side facing down, and a PEDOT:PSS solution was spin-coated on top of the graphene. The solution was vacuum dried and solidified to obtain a fifth sample. The fifth sample obtained was a PEDOT:PSS film, graphene, and a flexible substrate arranged in that order. The PEDOT:PSS spin-coating speed was 1000-5000 rpm, and the time was 5-60 s. f. Using the fifth sample, a copper wire is fixed to a PEDOT:PSS film using a conductive silver paste as an electrode to obtain a sixth sample; wherein the PEDOT:PSS film is connected to the copper wire via the conductive silver paste; g. Repeat steps a, b, and c to obtain the seventh sample; h. Place the seventh sample with the flexible substrate facing upward into an etching solution, etch away the metal substrate, and then clean the sample to obtain an eighth sample. The eighth sample has the graphene and the flexible substrate arranged from top to bottom. i. Use the side of the sixth sample with the PEDOT:PSS film facing up to fish out the eighth sample, vacuum dry it, and separate the hard plate to obtain the final sensor product. The sensor is the eighth sample placed on top of the sixth sample, that is, the flexible substrate, graphene, PEDOT:PSS film, graphene, and flexible substrate are arranged in order.

2. The method for preparing a graphene high-barrier flexible temperature sensor according to claim 1, wherein: The etching solution in step d and step h is ammonium persulfate or ferric chloride with a concentration of 0.1-3 mol / L; etching in step d and step h is performed twice, the first etching time is 1-3 hours, and the second etching time is 1-20 hours.

3. The method for preparing a graphene high-barrier flexible temperature sensor according to claim 1, wherein: The spin coating speed in step b is 100-2000 rpm, and the time is 5-60 s.

4. The method for preparing a graphene high-barrier flexible temperature sensor according to claim 3, wherein: The vacuuming time in step c is 5-30 min.

5. The method for preparing a graphene high-barrier flexible temperature sensor according to claim 3, wherein: The power of the bombardment plasma in step c is low gear, the power of the low gear is 7.16W, and the bombardment time is 10-60min.

6. The method for preparing a graphene high-barrier flexible temperature sensor according to claim 3, wherein: The metal substrate in step a is one of copper, nickel, platinum, cobalt, iron, molybdenum, ruthenium or iridium.

7. The method for preparing a graphene high-barrier flexible temperature sensor according to claim 1, wherein: The hard plate in step d is a quartz plate.

8. The method for preparing a graphene high-barrier flexible temperature sensor according to claim 1, wherein: The specific operation of the cleaning step in step d is: first use ultrapure water to clean once, then use a 1:1:20 solution of hydrochloric acid, hydrogen peroxide, and water to clean once, the time is 5-60 minutes, and then use ultrapure water to clean three times, each time for 1-30 minutes.

9. The method for preparing a graphene high-barrier flexible temperature sensor according to claim 1, wherein: In step b, the heating and curing temperature is 60-90° C. and the time is 10-60 minutes.

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