Flexible temperature sensor and method of manufacturing the same

Abstract

The application provides a flexible temperature sensor and a preparation method thereof. The sensor comprises a lower flexible substrate, two electrodes, a temperature-sensitive conductive composite film layer, a middle insulating layer and an upper flexible packaging layer. The middle insulating layer is fixed on the lower flexible substrate, and the upper flexible packaging layer is arranged on the middle insulating layer. One end of the middle insulating layer is provided with an opening, and the opening and the lower flexible substrate form a groove structure. The two electrodes are fixed on the lower flexible substrate and located at two ends of the opening of the middle insulating layer. The temperature-sensitive conductive composite film layer is coated in the groove structure of the lower flexible substrate between the two electrodes, and the temperature-sensitive conductive composite film layer is connected with the two electrodes respectively. The flexible temperature sensor has the advantages of wide temperature detection range, simple preparation, low cost, arbitrary size and shape, high sensitivity, stability and good repeatability.

Description

Technical Field

[0001] This invention relates to the field of flexible temperature sensor technology, and in particular to a flexible temperature sensor and its fabrication method. Background Technology

[0002] Temperature is the most fundamental physical parameter reflecting the state of a measured object and its surrounding environment. It characterizes the degree of hotness or coldness of an object and is inextricably linked to the properties and state of matter. Temperature measurement and monitoring are of paramount importance in metallurgy, petroleum, chemical, agricultural production, medical, and aerospace fields, playing an irreplaceable role in ensuring product quality, improving production efficiency, saving energy, and ensuring safe production. Although there are already sensing devices that detect temperature through certain physical changes, such as thermocouples, resistance temperature detectors (RTDs), and thermistors, and these have a wide range of applications, their temperature-sensitive elements use rigid materials such as ceramics and metals as substrates, resulting in poor flexibility, heavy weight, and inability to measure temperature on curved surfaces, making them unsuitable for today's complex application scenarios. Therefore, flexible temperature sensors have become one of the research hotspots both domestically and internationally.

[0003] Currently, commonly used flexible temperature sensing materials mainly include liquid metal, metal nanowires, carbon nanotubes, and graphene. In the key fabrication technology of flexible temperature sensors, patterning, transfer printing and other techniques are often used. Therefore, there are disadvantages such as high fabrication cost and poor repeatability.

[0004] In addition, existing flexible sensor devices are large in size, which is not conducive to temperature monitoring in small and complex environments.

[0005] In terms of performance, temperature-sensitive devices made of a single material often suffer from low sensitivity and narrow temperature detection range. While temperature-sensitive materials composed of multiple materials can improve the sensitivity of the sensor to some extent, such sensors often suffer from decreased sensitivity and stability due to the instability of the conductive cross-linked network of the temperature-sensitive composite material, which causes the blockage of the conductive path. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a flexible temperature sensor and its fabrication method.

[0007] The technical solution of this invention is as follows: a flexible temperature sensor, comprising a lower flexible substrate, two electrodes, a temperature-sensitive conductive composite thin film layer, a middle insulating layer, and an upper flexible encapsulation layer; the middle insulating layer is fixed on the lower flexible substrate, and the upper flexible encapsulation layer is disposed on the middle insulating layer; one end of the middle insulating layer has an opening, and the opening and the lower flexible substrate form a groove structure; the two electrodes are fixed on the lower flexible substrate and located at both ends of the opening in the middle insulating layer; the temperature-sensitive conductive composite thin film layer is coated within the groove structure of the lower flexible substrate between the two electrodes, and the temperature-sensitive conductive composite thin film layer is also connected to the two electrodes respectively.

[0008] Preferably, the two electrodes are made of metal or carbon powder and are fixed to the lower flexible substrate by nanoimprinting or screen printing.

[0009] Preferably, the lower flexible substrate and the middle insulating layer are made of polyimide or polyester film as the substrate.

[0010] Preferably, the upper flexible encapsulation layer is made of polyimide.

[0011] Preferably, the thickness of the lower flexible substrate is 0.07 to 0.235 mm.

[0012] Preferably, the thickness of the middle insulating layer is 0.07–0.235 mm.

[0013] Preferably, the thickness of the upper flexible encapsulation layer is 0.025–0.3 mm.

[0014] Preferably, the present invention also provides a method for fabricating a flexible temperature sensor, comprising the following steps:

[0015] S1) The lower flexible substrate, middle insulating layer and flexible encapsulation layer materials are cleaned and dried using ethanol and water in ultrasonic mode, and the middle insulating layer is opened.

[0016] S2) The two electrodes are fixed between the lower flexible substrate and the pre-drilled middle insulating layer by nanoimprinting or screen printing.

[0017] S3) Prepare a temperature-sensitive conductive composite film and coat it into the groove structure formed by the opening of the middle insulating layer and the lower flexible substrate;

[0018] S4) A flexible encapsulation layer is pressed on top of the temperature-sensitive conductive composite film layer and the middle insulating layer.

[0019] Preferably, the two electrodes are made of metal or carbon powder, with a volatile slurry as the adhesive, and are fixed to the lower flexible substrate by nanoimprinting or screen printing.

[0020] Preferably, the temperature-sensitive conductive composite film is made of porous carbon and polymer as the temperature-sensitive material.

[0021] Preferably, the temperature-sensitive conductive composite film is prepared as follows:

[0022] S31) Porous carbon, polymer, solvent and dispersant are mixed in a beaker at a mass ratio of 1:2:0.1 to 1:8:0.1, and the mixture is stirred on a magnetic stirrer for 2 to 4 hours at a temperature of 20 to 30°C. Then the mixture is placed in a vacuum degassing machine for 5 to 10 minutes to obtain a viscous porous carbon-based thermosensitive slurry.

[0023] S32) A porous carbon-based thermosensitive paste is uniformly coated into the groove formed by the pre-drilled middle insulating layer and the lower flexible substrate, covering the two electrodes. Then it is placed in a vacuum drying oven and dried at 200°C for 0.5 h to obtain a porous carbon-based thermosensitive conductive composite film.

[0024] Preferably, in step S31), the porous carbon is one or more of the following: bio-based, lignin-based, alkynyl-based, graphene-based, and metal-organic frameworks and their derived microporous carbon, mesoporous carbon, macroporous carbon, and multilayer porous carbon.

[0025] The polymer is one or more of the following: epoxy resin, polyurethane resin, silicone resin, unsaturated polyester resin, acrylic resin, polyvinyl acetal resin, and polyimide resin.

[0026] The solvent is at least one of the organic solvents including aromatic hydrocarbons, aliphatic hydrocarbons, esters, and ketones, and the dispersant is one or a combination of fatty acids, aliphatic amides, and low molecular weight polymer waxes.

[0027] Preferably, in step S31), the porous carbon is a carbon material doped with impurity ions. The doping with impurity ions means that the impurity ions are inevitably introduced into the material, or that the material has undergone additional doping treatment to incorporate more impurity ions.

[0028] Preferably, in step S32), the coating method of the porous carbon-based temperature-sensitive paste includes any one of drop coating, scraping coating, inkjet printing, electrohydraulic inkjet printing, mask coating, and screen printing.

[0029] Preferably, in step S32), the resistance of the temperature-sensitive conductive composite film exhibits a negative temperature coefficient characteristic, meaning the resistance between its two ends decreases as the temperature increases. The uniformly distributed impurity ions in the temperature-sensitive conductive composite film ionize at room temperature, forming positive or negative charge centers. A local electric field is generated near these impurity ions, causing charge carriers to experience Coulomb attraction or repulsion near the impurity centers, altering their direction and velocity. This process is called impurity scattering. This impurity scattering is affected by temperature; as the temperature increases, the scattering effect weakens, and the carrier mobility increases. Macroscopically, this manifests as a decrease in the resistance of the temperature-sensitive conductive composite film, and the trend is negatively correlated with temperature.

[0030] The beneficial effects of this invention are as follows:

[0031] 1. The temperature-sensitive conductive composite film of the present invention uses porous carbon and polymer as temperature-sensitive conductive materials. Its preparation process is simple. Porous carbon is prepared by ion doping and high-temperature carbonization. No other materials need to be modified on its surface to achieve temperature sensing characteristics, thus avoiding the limitation of temperature measurement accuracy caused by the uniformity of the modified materials.

[0032] 2. The porous carbon of the present invention has low preparation cost, large specific surface area, and a three-dimensional cross-linked structure that can adsorb with polymers to form a good conductive network, thereby increasing the resistance temperature change rate of the flexible sensor and improving the sensitivity of the flexible sensor to temperature changes.

[0033] 3. The shape and size of the temperature-sensitive element of the flexible temperature sensor of the present invention are determined according to the opening, which can realize patterning and fabrication of miniature sensors; the flexible temperature sensor of the present invention has a wide temperature detection range and can be used to detect -270℃ to 100℃. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the flexible temperature sensor of the present invention;

[0035] Figure 2 This is a side view of the flexible temperature sensor of the present invention;

[0036] Figure 3 This is a flowchart of the method of the present invention;

[0037] Figure 4 This is a SEM image of the temperature-sensitive conductive film of the present invention;

[0038] Figure 5 This is a temperature response range curve of the flexible temperature sensor of the present invention;

[0039] Figure 6The graph shows the response time of the flexible temperature sensor of the present invention from room temperature to ultra-low temperature (26℃ to -196℃).

[0040] In the figure, 1 – temperature-sensitive conductive thin film layer; 2 – lower flexible substrate; 3 – connection point; 4 – electrode; 5 – middle insulating layer; 6 – opening; 7 – metal sheet; 8 – upper flexible encapsulation layer. Detailed Implementation

[0041] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0042] Example 1

[0043] like Figure 1 and 2 As shown, this embodiment provides a flexible temperature sensor, including a lower flexible substrate 2, two electrodes 4, a temperature-sensitive conductive composite film layer 1, a middle insulating layer 5, and an upper flexible encapsulation layer 8. The middle insulating layer 5 is fixed to the lower flexible substrate 2, and the upper flexible encapsulation layer 8 is disposed on the middle insulating layer 5. One end of the middle insulating layer 5 has an opening 6, which, together with the lower flexible substrate 2, forms a groove structure. The two electrodes 4 are fixed to the lower flexible substrate 2 and located at both ends of the opening 6 in the middle insulating layer 5. The temperature-sensitive conductive composite film layer 1 is coated within the groove structure of the lower flexible substrate 2 between the two electrodes 4, and the temperature-sensitive conductive composite film layer 1 forms good contact connection points 3 with the two electrodes 4, thereby connecting the temperature-sensitive conductive composite film layer 1 to the two electrodes 4 respectively. One end of each electrode 4 has a metal sheet 7.

[0044] In a preferred embodiment, the two electrodes 4 are made of metal or carbon powder and embedded in copper sheets or copper wires; and are fixed to the lower flexible substrate 2 by nanoimprinting or screen printing.

[0045] In a preferred embodiment, the lower flexible substrate 2 and the middle insulating layer 5 are made of polyimide or polyester film as the substrate.

[0046] In a preferred embodiment, the upper flexible encapsulation layer 8 is made of polyimide.

[0047] In this preferred embodiment, the thickness of the lower flexible substrate 2 is 0.07 to 0.235 mm.

[0048] In this preferred embodiment, the thickness of the middle insulating layer 5 is 0.07–0.235 mm.

[0049] In this preferred embodiment, the thickness of the upper flexible encapsulation layer 8 is 0.025–0.3 mm.

[0050] Example 2

[0051] like Figure 3 As shown, this embodiment provides a method for fabricating a flexible temperature sensor, including the following steps:

[0052] S1) Clean the materials of the lower flexible substrate 2, the middle insulating layer 5 and the upper flexible encapsulation layer 8 with ethanol and water in ultrasonic mode for 5 minutes, and dry them. Then, make an opening 6 in the middle insulating layer 5.

[0053] S2) The two electrodes 4 are fixed between the lower flexible substrate 2 and the middle insulating layer 5 with pre-drilled holes 6 by nanoimprinting or screen printing.

[0054] S3) Prepare a temperature-sensitive conductive composite film and coat it into the groove structure formed by the opening 6 of the middle insulating layer 5 and the lower flexible substrate 2.

[0055] S4) An upper flexible encapsulation layer 8 is pressed on top of the temperature-sensitive conductive composite film layer 1 and the middle insulating layer 5.

[0056] After the sensor device is completed, it needs to be packaged and tested. The fabricated device can be applied to specific scenarios involving temperature detection on irregular surfaces. The flexible temperature sensor is placed on a variable temperature stage to test its temperature response range curve. Please refer to [link to relevant documentation]. Figure 5 The graph shows the temperature response range of the flexible temperature sensor of this invention. As can be seen from the graph, the flexible sensor of this invention is a negative temperature coefficient type, meaning its resistance decreases as temperature increases. Furthermore, the flexible temperature sensor of this invention can be used to detect temperatures in the range of -170℃ to 30℃, demonstrating its wide temperature detection range. The response time curve of this invention from room temperature to ultra-low temperature (26℃ to -196℃) can be found in [reference needed]. Figure 6 As shown, the flexible temperature sensor of the present invention has a response time of only ~1.5s from room temperature to ultra-low temperature (26℃ to -196℃) (response time refers to the time when the resistance of the sensor reaches 90% of the resistance change value when it comes into contact with the object being measured). This demonstrates that the flexible temperature sensor of the present invention has a fast temperature response speed and high sensitivity.

[0057] In a preferred embodiment, the two electrodes 4 are made of metal or carbon powder, with a volatile slurry as the adhesive, and are fixed to the lower flexible substrate 2 by nanoimprinting or screen printing.

[0058] In this preferred embodiment, the temperature-sensitive conductive composite film is prepared as follows:

[0059] S31) Porous carbon ZIF-8, polymer, and dispersant were mixed in a beaker at a ratio of 1:6:0.1 to prepare a mixture; the mixture was then stirred on a magnetic stirrer for 4 hours at a temperature of 26°C, and then placed in a vacuum degassing machine for 5 minutes to obtain a viscous porous carbon-based thermosensitive slurry;

[0060] (S32) A porous carbon-based thermosensitive paste is uniformly coated into the groove formed by the middle insulating layer 5 and the lower flexible substrate 2 of the pre-drilled holes 6, covering the two electrodes 4. It is then placed in a vacuum drying oven and dried at 200°C for 0.5 hours to volatilize some of the paste's adhesive material, thus obtaining a porous carbon-based thermosensitive conductive composite film. The SEM image of the porous carbon-based thermosensitive conductive composite film prepared in this embodiment can be found in [reference needed]. Figure 4 As shown in the figure, porous carbon ZIF-8 nanoparticles, due to their large specific surface area, three-dimensional cross-linked structure, and tight adsorption with polymers, form a good conductive network, thereby increasing the resistance temperature change rate of the flexible sensor.

[0061] The embodiments and descriptions above are merely illustrative of the principles and preferred embodiments of the present invention. Various changes and modifications may be made to the present invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed.

Claims

1. A flexible temperature sensor, characterized in that: The system includes a lower flexible substrate (2), two electrodes (4), a temperature-sensitive conductive composite film layer (1), a middle insulating layer (5), and an upper flexible encapsulation layer (8). The middle insulating layer (5) is fixed on the lower flexible substrate (2), and the upper flexible encapsulation layer (8) is disposed on the middle insulating layer (5). The middle insulating layer (5) has an opening (6) at one end, and the opening (6) and the lower flexible substrate (2) form a groove structure. The two electrodes (4) are fixed on the lower flexible substrate (2) and located at both ends of the opening (6) of the middle insulating layer (5). The temperature-sensitive conductive composite film layer (1) is coated in the groove structure of the lower flexible substrate (2) between the two electrodes (4), and the temperature-sensitive conductive composite film layer (1) is also connected to the two electrodes (4) respectively. The temperature-sensitive conductive composite film layer (1) is made of porous carbon and polymer as temperature-sensitive materials, and the porous carbon is a carbon material doped with impurity ions.

2. The flexible temperature sensor according to claim 1, characterized in that: The thickness of the lower flexible substrate (2) is 0.07 to 0.235 mm; the thickness of the middle insulating layer (5) is 0.07 to 0.235 mm; and the thickness of the upper flexible encapsulation layer (8) is 0.025 to 0.3 mm.

3. A method for fabricating a flexible temperature sensor, characterized in that: The method for preparing the flexible temperature sensor according to any one of claims 1-2 includes the following steps: S1) The materials of the lower flexible substrate (2), the middle insulating layer (5) and the upper flexible encapsulation layer (8) are cleaned and dried using ethanol and water in ultrasonic mode, and the middle insulating layer (5) is opened (6). S2) The two electrodes (4) are fixed between the lower flexible substrate (2) and the middle insulating layer (5) of the pre-drilled hole (6) by nanoimprinting or screen printing. S3) Prepare a temperature-sensitive conductive composite film and coat it in the groove structure formed by the opening (6) of the middle insulating layer (5) and the lower flexible substrate (2); S4) An upper flexible encapsulation layer (8) is pressed on top of the temperature-sensitive conductive composite film layer (1) and the middle insulating layer (5).

4. The method for fabricating a flexible temperature sensor according to claim 3, characterized in that: The two electrodes (4) are made of metal or carbon powder, with volatile paste as the adhesive, and are fixed to the lower flexible substrate (2) by nanoimprinting or screen printing.

5. The method for fabricating a flexible temperature sensor according to claim 3, characterized in that: The lower flexible substrate (2) and the middle insulating layer (5) are made of polyimide or polyester film as substrates; the upper flexible encapsulation layer (8) is made of polyimide.

6. The method for fabricating a flexible temperature sensor according to claim 5, characterized in that: The thermosensitive conductive composite film is prepared as follows: S31) Porous carbon, polymer, solvent and dispersant are mixed in a beaker at a mass ratio of 1:2:0.1 to 1:8:0.1, and the mixture is stirred on a magnetic stirrer for 2 to 4 hours at a temperature of 20 to 30 °C. Then the mixture is placed in a vacuum degassing machine for 5 to 10 minutes to obtain a viscous porous carbon-based thermosensitive slurry. S32) A porous carbon-based thermosensitive paste is uniformly coated into the groove formed by the middle insulating layer (5) and the lower flexible substrate (2) of the pre-opened hole (6), and covers the two electrodes (4). Then it is placed in a vacuum drying oven and dried at 200 °C for 0.5 h to obtain a porous carbon-based thermosensitive conductive composite film. The resistance of the thermosensitive conductive composite film has a negative temperature coefficient characteristic, and the resistance between its two ends will decrease as the temperature increases.

7. The method for fabricating a flexible temperature sensor according to claim 6, characterized in that: In step S31), the porous carbon is one or more of the following: bio-based, lignin-based, alkynyl-based, graphene-based, and metal-organic frameworks and their derived microporous carbon, mesoporous carbon, macroporous carbon, and multilayer porous carbon. The polymer is one or more of the following: epoxy resin, polyurethane resin, silicone resin, unsaturated polyester resin, acrylic resin, polyvinyl acetal resin, and polyimide resin. The solvent is at least one of the organic solvents including aromatic hydrocarbons, aliphatic hydrocarbons, esters, and ketones, and the dispersant is one or a combination of fatty acids, aliphatic amides, and low molecular weight polymer waxes.

8. The method for fabricating a flexible temperature sensor according to claim 7, characterized in that: In step S31), the doping of impurity ions refers to the inevitable introduction of impurity ions into the material, or the further doping treatment that has been performed to incorporate more impurity ions into the material.

9. The method for fabricating a flexible temperature sensor according to claim 8, characterized in that: In step S32), the coating method of the porous carbon-based temperature-sensitive paste includes any one of drop coating, scraping coating, inkjet printing, electrohydraulic inkjet printing, mask coating, and screen printing.

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