High performance flexible piezoresistive pressure sensor and preparation method thereof

Abstract

The application discloses a high-performance flexible piezoresistive pressure sensor and a preparation method, relates to the technical field of flexible pressure sensing, and comprises an upper flexible packaging layer, an upper sensing electrode, a composite microstructure sensing layer, a lower sensing electrode and a lower flexible packaging layer. The composite microstructure sensing layer is provided with an array of concave micro-hemispheres arranged symmetrically upwards and downwards. By utilizing the stress concentration effect of the concave structure and the synergistic deformation mechanism of the elastomer material, efficient transformation of the microstructure from linear contact to stable surface contact during the pressure process is realized. Compared with traditional plane, convex or pointed microstructure, the application significantly improves the pressure response sensitivity, and the symmetrical structure ensures the uniformity of deformation and the stability of signal output, effectively solves the problems of low pressure area response insensitivity and signal drift in the prior art, and is especially suitable for dynamic pressure detection scenes.

Description

Technical Field

[0001] This invention relates to the field of flexible pressure sensing technology, specifically to a high-performance flexible piezoresistive pressure sensor and its fabrication method. Background Technology

[0002] With the rapid development of flexible electronics, wearable devices, and other fields, the demand for comprehensive performance characteristics such as high sensitivity, wide detection range, fast response speed, and long-term stability in flexible piezoresistive pressure sensors is becoming increasingly urgent. However, traditional design schemes relying on single materials are difficult to meet the accurate sensing requirements of diverse application scenarios. Although some progress has been made, existing technologies still face bottlenecks such as insufficient sensitivity, dynamic response lag, and insufficient cycle stability.

[0003] Structural innovation is a key path to achieving breakthroughs in the performance of flexible pressure sensors. By controlling the microstructure of the sensing layer or electrode layer, the stress distribution and conductivity response mechanism under pressure can be effectively optimized. On the one hand, the deformation amplification effect can improve sensitivity and lower the detection limit; on the other hand, this strategy can also meet the application requirements of a wide detection range. Currently, microstructure designs based on elastic materials widely adopt convex structures such as pyramids, columns (including cylinders and square prisms), or pyramids. Under pressure, although the material undergoes elastic deformation as the compressive load increases, the contact area expansion is limited due to geometric topological constraints, making it difficult to efficiently transform into stable surface contact. Furthermore, these microstructures are difficult to self-adjust their contact state under slight tilting or dynamic disturbances, easily leading to contact failure or local microstructure detachment, which severely restricts sensor performance.

[0004] Therefore, a high-performance flexible piezoresistive pressure sensor and its fabrication method are proposed to solve the above problems. Summary of the Invention

[0005] To achieve the above objectives, the present invention provides the following technical solution: a method for fabricating a high-performance flexible piezoresistive pressure sensor, comprising the following steps: Step 1: After cleaning and drying the transparent polyethylene terephthalate film, cut it to the required size to obtain the upper flexible encapsulation layer and the lower flexible encapsulation layer. Step 2: The upper sensing electrode is formed on one side of the upper flexible encapsulation layer and the lower sensing electrode is formed on one side of the lower flexible encapsulation layer by means of screen printing, magnetron sputtering or spraying. Step 3: Add carbon nanotubes to polydimethylsiloxane prepolymer solution and stir for 1 hour until uniformly dispersed. Then add curing agent and stir manually to obtain a uniform mixture. Pour the mixture into a resin mold, smooth it with a scraper, place the mold in a vacuum dryer to remove air bubbles, and then place it in an oven at 70-80℃ for 2-3 hours to cure. After cooling, peel it off to obtain a single-layer microstructure sensing film. The microstructure sensing film includes a flat, thin film-like base surface and multiple concave micro-hemisphericals uniformly formed on one side of the base surface. The concave micro-hemisphericals are hemispherical in shape, and the top of the concave micro-hemisphericals is concave inward. Prepare another layer of microstructure sensing film using the same process. Place the base surfaces of the two microstructure sensing films together and coat a layer of mixture between the two microstructure sensing films as a bonding layer. Place it in an oven at 80℃ for 1 hour to cure again to obtain a symmetrical composite microstructure sensing layer. Step 4: Make the upper sensing electrode and the lower sensing electrode contact and attach to the upper and lower sides of the composite microstructure sensing layer, respectively, and seal the sides of the upper flexible encapsulation layer, the composite microstructure sensing layer, and the lower flexible encapsulation layer with adhesive to obtain a high-performance flexible piezoresistive pressure sensor.

[0006] Preferably, step 1 involves ultrasonically cleaning the transparent polyethylene terephthalate film with anhydrous ethanol and deionized water for 10-15 minutes each, drying it, and then cutting it to the required size to obtain the upper flexible encapsulation layer and the lower flexible encapsulation layer.

[0007] Preferably, in step 1, the thickness of the transparent polyethylene terephthalate film is 50–500 μm.

[0008] As a preferred option, step 2 specifically involves: One side of the upper and lower flexible encapsulation layers is used as the treatment surface and oxygen plasma activation treatment is performed. The treatment power is set to 50-100W and the time is 30-60s. Subsequently, sensing electrodes are prepared on the treatment surfaces of the upper and lower flexible encapsulation layers by screen printing, magnetron sputtering or spraying. The upper sensing electrode is prepared on the treatment surface of the upper flexible encapsulation layer and the lower sensing electrode is prepared on the treatment surface of the lower flexible encapsulation layer. The upper and lower flexible encapsulation layers are then dried in an oven at 60-80℃ for 30-45min. Finally, conductive wires are led out from the electrode lead-out ports of the upper and lower sensing electrodes, respectively.

[0009] Preferably, in step 3, the mass ratio of carbon nanotubes to polydimethylsiloxane prepolymer is 1:100, and the mass ratio of polydimethylsiloxane prepolymer to curing agent is 10:1.

[0010] Preferably, the conductive wire in step 2 is one of copper foil, solid metal wire coated with silver paste, silver wire, or conductive cloth tape, and one end of the conductive wire is fixed to the surface of the corresponding sensing electrode by conductive silver paste.

[0011] The present invention also provides a high-performance flexible piezoresistive pressure sensor, which is prepared by the method described above.

[0012] The present invention has the following beneficial effects: The composite microstructure sensing layer of this invention features a symmetrically arranged array of concave micro-hemispherical structures. Utilizing the stress concentration effect of the concave structure and the synergistic deformation mechanism of the elastomer material, it achieves an efficient transition from line contact to stable surface contact during pressure application. Compared to traditional planar, convex, or pointed microstructures, this invention significantly improves pressure response sensitivity. Simultaneously, the symmetrical structure ensures uniform deformation and stable signal output, effectively solving problems such as insensitivity in low-pressure areas and signal drift in existing technologies. It is particularly suitable for dynamic pressure detection scenarios.

[0013] The preparation method of the present invention has good controllability and large-scale production capability, which facilitates mass production. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the overall structure of the high-performance flexible piezoresistive pressure sensor of the present invention; Figure 2 This is a partial structural diagram of the composite microstructure sensing layer in this invention; Figure 3 This is a schematic diagram illustrating the working mechanism of the present invention; Figure 4 This is a schematic diagram showing the contact changes between the sensing electrode and the composite microstructure sensing layer in this invention.

[0015] In the figure: 1, upper flexible encapsulation layer; 2, upper sensing electrode; 3, composite microstructure sensing layer; 4, lower sensing electrode; 5, lower flexible encapsulation layer. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0018] Example 1: refer to Figure 1This embodiment provides a high-performance flexible piezoresistive pressure sensor, which consists of, from top to bottom, an upper flexible encapsulation layer 1, an upper sensing electrode 2, a composite microstructure sensing layer 3, a lower sensing electrode 4, and a lower flexible encapsulation layer 5. The upper and lower sides of the composite microstructure sensing layer 3 are in contact with and bonded to the upper sensing electrode 2 and the lower sensing electrode 4, respectively. The sides of the upper flexible encapsulation layer 1, the composite microstructure sensing layer 3, and the lower flexible encapsulation layer 5 are sealed with adhesive. The composite microstructure sensing layer 3 adopts a two-layer symmetrical arrangement design, that is, the first microstructure sensing film and the second microstructure sensing film are arranged opposite to each other, and the outer surface of both layers is formed with an array of concave micro-hemispherical structures. In the uncompressed state, the concave micro-hemispherical structures on the upper and lower sides are in contact with the upper sensing electrode 2 and the lower sensing electrode 4, respectively.

[0019] This embodiment also provides a method for fabricating a high-performance flexible piezoresistive pressure sensor, comprising the following steps: Step 1: Select a transparent polyethylene terephthalate film with a thickness of 200 μm, and clean it with anhydrous ethanol and deionized water for 10-15 min each. After drying, cut it into the required size to obtain the upper flexible encapsulation layer 1 and the lower flexible encapsulation layer 5. Step 2: One side of the upper flexible encapsulation layer 1 and the lower flexible encapsulation layer 5 is used as the treatment surface and oxygen plasma activation treatment is performed. The treatment power is set to 60W and the time is 60s to improve the surface hydrophilicity and the adhesion of the electrode material. Subsequently, under the protection of argon atmosphere, gold layers are deposited on the treatment surfaces of the upper flexible encapsulation layer 1 and the lower flexible encapsulation layer 5 by magnetron sputtering to prepare sensing electrodes. The sputtering power is 100W and the time is 120s. The upper flexible encapsulation layer 1 is used to prepare the upper sensing electrode 2 and the lower flexible encapsulation layer 5 is used to prepare the lower sensing electrode 4. After the gold plating is completed, the upper flexible encapsulation layer 1 and the lower flexible encapsulation layer 5 are placed in an 80℃ oven to dry for 30min. Finally, conductive silver paste is coated on the electrode lead-out ports of the upper sensing electrode 2 and the lower sensing electrode 4, and conductive silver wires are led out as external connection wires. Step 3: Clean the 3D-printed resin mold by soaking it in isopropanol and drying it with nitrogen gas; weigh 0.1g of carbon nanotubes and add 10g of polydimethylsiloxane. Prepolymer liquidStir for 1 hour until uniformly dispersed, then add 1g of curing agent and stir manually for 10 minutes to obtain a uniform mixture. Pour the mixture containing conductive filler and elastomer substrate into a resin mold and smooth it with a scraper to ensure that the mixture fully fills the groove of the mold. Place the mold in a vacuum dryer to remove air bubbles for 20 minutes, then place it in an 80℃ oven to cure for 3 hours. After removing it and cooling it to room temperature, peel it off to obtain a single-layer microstructure sensing film. The microstructure sensing film includes a flat thin film base surface and multiple concave micro-hemisphericals uniformly formed on one side of the base surface. The concave micro-hemisphericals are hemispherical in shape, and the top of the concave micro-hemisphericals is concave inward. Prepare another layer of microstructure sensing film using the same process. Place the base surfaces of the two microstructure sensing films together (with the concave micro-hemisphericals facing outward), and coat a layer of mixture between the two microstructure sensing films as a bonding layer. Place it in an 80℃ oven to cure for 1 hour again to obtain a symmetrical composite microstructure sensing layer 3. Step 4: Stack the upper flexible encapsulation layer 1, the composite microstructure sensing layer 3, and the lower flexible encapsulation layer 5 together, so that the upper sensing electrode 2 and the lower sensing electrode 4 are respectively in contact with and attached to the upper and lower sides of the composite microstructure sensing layer 3, and seal the sides of the upper flexible encapsulation layer 1, the composite microstructure sensing layer 3, and the lower flexible encapsulation layer 5 with adhesive to obtain a high-performance flexible piezoresistive pressure sensor.

[0020] refer to Figure 2 The diagram shows a partial structure of the composite microstructure sensing layer 3 of the high-performance flexible piezoresistive pressure sensor in this embodiment. The composite microstructure sensing layer 3 adopts a symmetrical concave micro-hemispherical array design. The concave micro-hemispherical structures (concave surface facing the center of the interlayer) are uniformly distributed on the surface of the upper and lower sensing layers. The conductive filler (carbon nanotubes) is uniformly dispersed in polydimethylsiloxane matrix, which can form a continuous conductive path.

[0021] refer to Figure 3This is a schematic diagram illustrating the working mechanism of the high-performance flexible piezoresistive pressure sensor in this embodiment. Initially, the upper and lower sensing electrodes only form local edge contact with the surface of the composite microstructure sensing layer 3. The current between the upper sensing electrode 2 and the lower sensing electrode 4 is conducted through a small number of interconnected conductive pathways in the composite microstructure sensing layer 3. When external pressure is applied to the device surface, the pressure is transmitted to the composite microstructure sensing layer 3 via the upper sensing electrode 2. The upper concave micro-hemispherical layer first undergoes edge compression, and as the pressure gradually increases, the upper concave micro-hemispherical layer continues to indent downwards. The overall structure is stretched out, and the lower concave micro-hemispherical layer deforms upward in sync. Finally, the concave surfaces of the upper and lower micro-hemispherical layers are completely attached and in close contact with the corresponding electrode layers. During this process, the number of conductive paths formed by the conductive filler increases significantly and the contact area expands. The overall resistance (R) of the composite microstructure sensing layer 3 decreases significantly with increasing pressure. When the external pressure is removed, the elastic rebound force of the elastomer substrate and the "negative pressure rebound effect" of the concave micro-hemispherical layer work together to quickly restore the micro-hemispherical to its initial concave shape, and the resistance rises back to the initial level, achieving highly sensitive sensing.

[0022] refer to Figure 4 This diagram illustrates the contact changes between the sensing electrode and the composite microstructure sensing layer of the high-performance flexible piezoresistive pressure sensor in this embodiment. In the initial state (S0), the concave micro-hemispherical structure causes the composite microstructure sensing layer 3 to only form local edge contact with the sensing electrodes (upper sensing electrode 2 and lower sensing electrode 4), resulting in the smallest effective contact area and the highest initial resistance of the sensor. When pressure is applied, the micro-hemispherical undergoes elastic deformation, and the contact area between the composite microstructure sensing layer 3 and the sensing electrode gradually expands (S1). As the pressure continues to be applied, the composite microstructure sensing layer 3 and the sensing electrode achieve complete surface contact (S2), and the effective contact area reaches its maximum value. This gradient contact change, in conjunction with the stress concentration characteristics of the concave micro-hemispherical, enables efficient pressure detection and sensing.

[0023] The core advantages of the concave micro-hemispherical structure include: The concave design makes the deformation concentrated and controllable under pressure loading. Compared with planar or pointed structures, the change in the conductive path is more significant, which can greatly improve the sensitivity of the sensor. The upper and lower micro-hemispherical layers are symmetrically aligned, resulting in uniform deformation during pressure loading / unloading. This effectively avoids signal drift caused by abrupt changes in the conductive path on one side, thus improving the stability of the device.

[0024] Example 2: This embodiment is based on Embodiment 1, and uses the fabrication method of the high-performance flexible piezoresistive pressure sensor provided in Embodiment 1. The difference from Embodiment 1 is that the magnetron sputtering method in step 2 is changed to a spraying method, and the conductive material is replaced with MXene, with an MXene concentration of 5-15 mg / mL. Step 2 in this embodiment is specifically as follows: One side of the upper flexible encapsulation layer 1 and the lower flexible encapsulation layer 5 is used as the treatment surface and subjected to oxygen plasma activation treatment. The treatment power is set to 60W and the time is 60s to improve the surface hydrophilicity and the adhesion of the electrode material. Then, an MXene aqueous solution with a concentration of 5mg / mL is loaded into the spray gun reservoir. The distance between the spray gun nozzle and the substrate (upper flexible encapsulation layer 1 or lower flexible encapsulation layer 5) is adjusted to 15cm, and the atomization pressure is set to 0.2MPa. MXene coatings are deposited on the treatment surfaces of the upper flexible encapsulation layer 1 and the lower flexible encapsulation layer 5 by uniform spraying. The number of spraying passes is 3. The upper sensing electrode 2 is formed on the treatment surface of the upper flexible encapsulation layer 1, and the lower sensing electrode 4 is formed on the treatment surface of the lower flexible encapsulation layer 5. After the spraying is completed, the upper flexible encapsulation layer 1 and the lower flexible encapsulation layer 5 are placed in an 80℃ oven to dry for 30min. Finally, conductive silver paste is coated on the electrode lead-out ports of the upper sensing electrode 2 and the lower sensing electrode 4, and conductive silver wires are led out as external connection wires.

[0025] The remaining preparation process is the same as in Example 1.

[0026] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for fabricating a high-performance flexible piezoresistive pressure sensor, characterized in that, Includes the following steps: Step 1: After cleaning and drying the transparent polyethylene terephthalate film, cut it to the required size to obtain the upper flexible encapsulation layer (1) and the lower flexible encapsulation layer (5). Step 2: By screen printing, magnetron sputtering or spraying, a sensing electrode (2) is formed on one side of the upper flexible encapsulation layer (1) and a lower sensing electrode (4) is formed on one side of the lower flexible encapsulation layer (5). Step 3: Add carbon nanotubes to polydimethylsiloxane prepolymer liquid, stir for 1 hour until uniformly dispersed, then add curing agent and stir manually to obtain a uniform mixture; pour the mixture into resin mold, scrape it flat with a scraper, place the mold in a vacuum dryer to remove air bubbles, and then place it in an oven at 70-80℃ for 2-3 hours to cure. After cooling, peel it off to obtain a single-layer microstructure sensing film. The microstructure sensing film includes a flat thin film base surface and multiple concave micro-hemisphericals uniformly formed on one side of the base surface. The concave micro-hemisphericals are hemispherical in shape, and the top of the concave micro-hemisphericals is concave inward. Prepare another layer of microstructure sensing film according to the same process, attach the base surfaces of the two microstructure sensing films to each other, and coat a layer of mixture between the two microstructure sensing films as a bonding layer. Place it in an oven at 80℃ for 1 hour to obtain a symmetrical composite microstructure sensing layer (3). Step 4: Make the upper sensing electrode (2) and the lower sensing electrode (4) contact and attach to the upper and lower sides of the composite microstructure sensing layer (3) respectively, and seal the sides of the upper flexible encapsulation layer (1), the composite microstructure sensing layer (3), and the lower flexible encapsulation layer (5) with adhesive to obtain a high-performance flexible piezoresistive pressure sensor.

2. The method for fabricating a high-performance flexible piezoresistive pressure sensor according to claim 1, characterized in that, Step 1 is as follows: The transparent polyethylene terephthalate film is ultrasonically cleaned with anhydrous ethanol and deionized water for 10-15 minutes each, dried and cut into the required size to obtain the upper flexible encapsulation layer (1) and the lower flexible encapsulation layer (5).

3. The method for fabricating a high-performance flexible piezoresistive pressure sensor according to claim 2, characterized in that, In step 1, the thickness of the transparent polyethylene terephthalate film is 50–500 μm.

4. The method for fabricating a high-performance flexible piezoresistive pressure sensor according to claim 1, characterized in that, Step 2 is as follows: One side of the upper flexible encapsulation layer (1) and the lower flexible encapsulation layer (5) is used as the processing surface and oxygen plasma activation treatment is performed. The processing power is set to 50-100W and the time is 30-60s. Then, sensing electrodes are prepared on the processing surfaces of the upper flexible encapsulation layer (1) and the lower flexible encapsulation layer (5) by screen printing, magnetron sputtering or spraying. The upper flexible encapsulation layer (1) is used to prepare the upper sensing electrode (2) and the lower flexible encapsulation layer (5) is used to prepare the lower sensing electrode (4). The upper flexible encapsulation layer (1) and the lower flexible encapsulation layer (5) are then placed in an oven at 60-80℃ and dried for 30-45min. Finally, conductive wires are led out from the electrode lead-out ports of the upper sensing electrode (2) and the lower sensing electrode (4), respectively.

5. The method for fabricating a high-performance flexible piezoresistive pressure sensor according to claim 1, characterized in that, In step 3, the mass ratio of carbon nanotubes to polydimethylsiloxane prepolymer is 1:100, and the mass ratio of polydimethylsiloxane prepolymer to curing agent is 10:

1.

6. The method for fabricating a high-performance flexible piezoresistive pressure sensor according to claim 4, characterized in that, The conductive wire in step 2 is one of copper foil, solid metal wire coated with silver paste, silver wire, or conductive cloth tape. One end of the conductive wire is fixed to the surface of the corresponding sensing electrode by conductive silver paste.

7. A high-performance flexible piezoresistive pressure sensor, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 6.

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