Flexible capacitive pressure sensor with micro-nano array structure and preparation method thereof

Abstract

The invention discloses a flexible capacitive pressure sensor with a micro-nano array structure, which comprises a first electrode layer, a flexible dielectric layer, a second electrode layer and a flexible thin film layer which are sequentially stacked from top to bottom, and the flexible thin film layer is provided with the micro-nano array structure. By constructing the micro-nano structure, the sensitivity and the detection range of the pressure sensor are improved, and the pressure sensor has good stability and repeatability. The invention further discloses a preparation method of the flexible capacitive pressure sensor, the flexible thin film layer with the micro-nano array structure is prepared by modulating corona electric field treatment, a micro-nano structure template does not need to be additionally manufactured, the process is simple, the cost is low, and batch preparation can be achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of sensors, and in particular relates to a flexible capacitive pressure sensor with a micro-nano array structure and a preparation method thereof. Background Art

[0002] The rapid development of flexible pressure sensors has brought new application opportunities in the fields of motion monitoring, health monitoring, medical diagnosis, tactile perception, etc. In the current research on flexible pressure sensors, they are divided into the following main types according to their working principles: piezoresistive pressure sensors, capacitive pressure sensors, and piezoelectric pressure sensors. Compared with piezoelectric and piezoresistive flexible pressure sensors, capacitive pressure sensors have high sensitivity, fast response speed, good stability, small drift, and have a wider range of application prospects.

[0003] In order to further improve the sensitivity of the flexible capacitive sensor, a microstructure such as a pyramid structure, a columnar structure, a hemispherical structure, etc. is often constructed on the dielectric layer or the flexible electrode by a template method. For example, the Chinese patent with the publication number CN115096479A discloses a wearable pressure sensing device based on a capacitive flexible sensor, including a sensing module and a detection module; the sensing module includes a capacitive flexible sensing unit, the flexible sensing module includes two layers of flexible electrodes with microstructures and two layers of flexible dielectric layers, and micro-pyramid array electrodes, electrospun membrane dielectric layers, micro-column array dielectric layers and micro-groove array electrodes are stacked from top to bottom in sequence, the top and bottom flexible electrodes are composed of a silicon-based elastomer loaded with one-dimensional and two-dimensional conductive materials, and the flexible dielectric layer is composed of an electrospun membrane loaded with nanoparticles and a silicon-based elastomer with a microstructure; the detection module includes a circuit element for converting the capacitance change caused by pressure of the capacitive flexible sensing unit into a corresponding electrical signal, an electrical signal detection element, and a power supply and energy storage module; the invention improves the sensitivity and stability of the sensor by setting the electrode microstructure and introducing a double dielectric layer. And a Chinese patent with publication number CN115060406A discloses a flexible ion-type three-dimensional force sensor and a preparation method thereof, which relates to the technical field of three-dimensional force sensors, and includes a raised contact, a first layer electrode array, an ion gel film with a graded microstructure, and a second layer electrode array arranged in sequence; the ion gel film with the graded microstructure is located on the surface of the dielectric layer, and a square platform protrusion is added between the raised contact and the first layer electrode array, the graded microstructure includes a micro-hemispherical array, and each micro-hemispherical structure of the micro-hemispherical array is provided with a micro-pillar array.

[0004] The preparation of microstructure templates mostly uses photolithography, laser etching, electrospinning, etc., which are complex processes, expensive equipment and high energy consumption; in addition, most flexible pressure sensors have low sensitivity, narrow measurement range and high detection limit. Therefore, it is necessary to provide a flexible capacitive pressure sensor with simple process, low cost and high sensitivity. Summary of the invention

[0005] The object of the present invention is to provide a flexible capacitive pressure sensor with a micro-nano array structure and a preparation method thereof, thereby improving the sensitivity and detection range of the pressure sensor.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A high-sensitivity flexible capacitive pressure sensor with a micro-nano array structure comprises a first electrode layer, a flexible dielectric layer, a second electrode layer, and a flexible film layer which are stacked in sequence from top to bottom, wherein the flexible film layer has a micro-nano array structure.

[0008] Wherein, the flexible film layer is obtained by modulating corona electric field treatment; and the second electrode layer is deposited on the flexible film layer by ion beam sputtering process.

[0009] The micro-nano array structure is a regularly arranged concave-convex structure, the shape of the concave-convex structure is wavy, the height of the convex structure is 90-100 μm, and the height of the concave structure is 5-10 μm.

[0010] The material of the first electrode layer is PET / ITO conductive film, the material of the flexible dielectric layer is a mixture of terpolymer P (VDF-TrFE-CTFE) and 1-ethyl-3-methylimidazole bis(trifluoromethylsulfonyl)imide, the material of the second electrode layer is gold, and the material of the flexible film layer includes platinum catalyzed silica gel Ecoflex TM 00-30, one of polydimethylsiloxane PDMS.

[0011] Furthermore, the flexible film layer is obtained by modulating corona electric field treatment; and the second electrode layer is deposited on the flexible film layer by ion beam sputtering process.

[0012] Furthermore, the material of the flexible dielectric layer is a mixture of terpolymer P (VDF-TrFE-CTFE) and 1-ethyl-3-methylimidazole bis(trifluoromethylsulfonyl)imide [EMIM] [TFSI].

[0013] Preferably, the material of the first electrode layer is PET / ITO conductive film.

[0014] Preferably, the material of the second electrode layer is gold.

[0015] Preferably, the material of the flexible film layer is Ecoflex TM 00-30.

[0016] Preferably, the thickness of the first electrode layer is 150-200 μm, the thickness of the flexible dielectric layer is 10-20 μm, and the thickness of the second electrode layer is 40-80 nm.

[0017] The present invention also provides a method for preparing the above-mentioned flexible capacitive pressure sensor, comprising the following steps:

[0018] (1) spin coating a material of a flexible thin film layer on a conductive substrate, and continuously applying a modulated corona electric field while heating and curing the material to obtain a flexible thin film layer having a micro-nano array structure;

[0019] (2) peeling the flexible film layer obtained in step (1) from the conductive substrate and subjecting it to oxygen plasma treatment;

[0020] (3) depositing gold on the surface of the flexible thin film layer treated in step (2) by an ion beam sputtering process to prepare a second electrode layer;

[0021] (4) dissolving the terpolymer P (VDF-TrFE-CTFE) powder in an organic solvent, and adding 1-ethyl-3-methylimidazole bis (trifluoromethylsulfonyl) imide to obtain a mixture, and stirring the mixture until the P (VDF-TrFE-CTFE) is completely dissolved to obtain a uniform solution;

[0022] (5) spin coating the uniform solution obtained in step (4) on the first electrode layer, and then drying the first electrode layer after spin coating the solution on a hot plate to completely evaporate the organic solvent, thereby preparing a flexible dielectric layer;

[0023] (6) Encapsulating a first electrode layer formed with a flexible dielectric layer and a flexible film layer formed with a second electrode layer, and extracting electrode leads from the first electrode layer and the second electrode layer to obtain the sensor.

[0024] Preferably, in step (1), Ecoflex TM The volume ratio of agent A and agent B of 00-30 is 1:1, and the mixture is evenly degassed and spin-coated on a conductive substrate. The spin-coating speed is 200-800 rpm, and the spin-coating time is 10-40 s. The temperature condition for the solution to heat and solidify after spin coating is from room temperature to 70-90°C, and the heating rate is 3°C / min. After reaching the set temperature, the constant temperature is maintained for 10-20 minutes, and the electric field strength of the applied modulated corona electric field is 5-15 kV / cm.

[0025] Preferably, in step (2), the flexible film layer is treated with oxygen plasma at a power of 60 to 80 W for 2 to 10 min.

[0026] Preferably, in step (4), the amount of 1-ethyl-3-methylimidazole bis(trifluoromethylsulfonyl)imide added is 20% to 50% of the polyvinylidene fluoride based polymer powder, and the percentage is a mass percentage. Further preferably, the organic solvent is N,N-dimethylformamide, 1.5 g of polyvinylidene fluoride based polymer powder is dissolved in 10 mL of N,N-dimethylformamide, and 1-ethyl-3-methylimidazole bis(trifluoromethylsulfonyl)imide is added at a mass ratio of 20% to 50% of P(VDF-TrFE-CTFE).

[0027] Preferably, in step (5), the spin coating speed is 800-1200 rpm, the spin coating time is 20-50 s, and the hot plate temperature is set to 60-100°C.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The flexible capacitive pressure sensor provided by the present invention improves the sensitivity and detection range of the pressure sensor by constructing a micro-nano structure, and the micro-nano structure is evenly distributed and uniform in size, so that the prepared sensor has good stability and repeatability; the capacitive pressure sensor of the present invention uses a mixture of a ternary copolymer P (VDF-TrFE-CTFE) and 1-ethyl-3-methylimidazole bistrifluoromethylsulfonyl imide as a flexible dielectric layer material, thereby improving the variation of the sensor capacitance value; the capacitive pressure sensor provided by the present invention prepares a flexible film layer with a micro-nano array structure through corona electric field treatment, and assembles to obtain a sensor with a micro-nano structure, without the need to additionally prepare a micro-nano structure template, the process is simple, the cost is low, and batch preparation can be achieved; the capacitive pressure sensor provided by the present invention has high sensitivity within a large pressure range. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the layer structure of the flexible capacitive pressure sensor with a micro-nano array structure of the present invention, wherein 1-first electrode layer, 2-flexible dielectric layer, 3-second electrode layer, 4-flexible film layer;

[0031] Figure 2 It is a schematic diagram of the mechanism of the flexible capacitive pressure sensor of the present invention;

[0032] Figure 3 This is a SEM image of the micro-nano array structure on the surface of the flexible film layer of the present invention;

[0033] Figure 4 This is a sensitivity diagram of the flexible capacitive pressure sensor prepared in Example 1;

[0034] Figure 5 This is a response time diagram of the flexible capacitive pressure sensor prepared in Example 1;

[0035] Figure 6 This is a detection limit diagram of the flexible capacitive pressure prepared in Example 1;

[0036] Figure 7 This is a cyclic test diagram of the flexible capacitive pressure sensor prepared in Example 1. DETAILED DESCRIPTION

[0037] The technical solution of the present invention is further explained below in conjunction with specific embodiments.

[0038] Example 1

[0039] (1) Ecoflex TM 00-30 agent A and agent B were mixed evenly in a volume ratio of 1:1, degassed, and spin-coated on a conductive substrate at a spin-coating speed of 500 rpm and a spin-coating time of 20 s. After spin-coating, the temperature was raised to 80°C and kept at a constant temperature for 15 minutes. During the heating and constant temperature keeping process, a corona electric field with an electric field strength of 12 kV / cm was continuously applied to prepare a flexible thin film layer with a micro-nano array structure.

[0040] (2) peeling the flexible film layer obtained in step (1) from the conductive substrate and treating it with oxygen plasma at a power of 80 W for 5 minutes;

[0041] (3) depositing a gold layer with a thickness of about 60 nm on the surface of the flexible thin film layer treated in step (2) by an ion beam sputtering process to prepare a second electrode layer;

[0042] (4) 1.5 g of the terpolymer P(VDF-TrFE-CTFE) powder was dissolved in 10 mL of N,N-dimethylformamide, and 1-ethyl-3-methylimidazole bis(trifluoromethylsulfonyl)imide was added at a mass ratio of 30% of P(VDF-TrFE-CTFE) to obtain a mixture, and the mixture was stirred until P(VDF-TrFE-CTFE) was completely dissolved to obtain a uniform solution;

[0043] (5) spin coating the uniform solution obtained in step (4) on the first electrode layer at a spin coating speed of 1000 rpm for 30 seconds, and then drying the spin-coated first electrode layer on a hot plate at 80° C. to completely evaporate the organic solvent, thereby preparing a flexible dielectric layer;

[0044] (6) The first electrode layer formed with the flexible dielectric layer and the flexible film layer formed with the second electrode layer are packaged, and electrode leads are drawn from the first electrode layer and the second electrode layer to obtain a sensor.

[0045] In the flexible capacitive sensor prepared in this embodiment, the thickness of the first electrode layer is 180 μm, and the thickness of the flexible dielectric layer is 15 μm.

[0046] Example 2

[0047] (1) Ecoflex TM 00-30 agent A and agent B were mixed evenly in a volume ratio of 1:1, degassed, and spin-coated on a conductive substrate at a spin-coating speed of 500 rpm and a spin-coating time of 20 s. After spin-coating, the temperature was raised to 80°C and kept at a constant temperature for 15 minutes. During the heating and constant temperature keeping process, a corona electric field with an electric field strength of 10 kV / cm was continuously applied to prepare a flexible thin film layer with a micro-nano array structure.

[0048] (2) peeling the flexible film layer obtained in step (1) from the conductive substrate and treating it with oxygen plasma at a power of 80 W for 5 minutes;

[0049] (3) depositing a gold layer with a thickness of about 60 nm on the surface of the flexible thin film layer treated in step (2) by an ion beam sputtering process to prepare a second electrode layer;

[0050] (4) 1.5 g of the terpolymer P(VDF-TrFE-CTFE) powder was dissolved in 10 mL of N,N-dimethylformamide, and 1-ethyl-3-methylimidazole bis(trifluoromethylsulfonyl)imide was added at a mass ratio of 20% of P(VDF-TrFE-CTFE) to obtain a mixture, and the mixture was stirred until P(VDF-TrFE-CTFE) was completely dissolved to obtain a uniform solution;

[0051] (5) spin coating the uniform solution obtained in step (4) on the first electrode layer at a spin coating speed of 1000 rpm for 30 seconds, and then drying the spin-coated first electrode layer on a hot plate at 80° C. to completely evaporate the organic solvent, thereby preparing a flexible dielectric layer;

[0052] (6) The first electrode layer formed with the flexible dielectric layer and the flexible film layer formed with the second electrode layer are packaged, and electrode leads are drawn from the first electrode layer and the second electrode layer to obtain a sensor.

[0053] In the flexible capacitive sensor prepared in this embodiment, the thickness of the first electrode layer is 150 μm, and the thickness of the flexible dielectric layer is 15 μm.

[0054] Example 3

[0055] (1) Ecoflex TM 00-30 agent A and agent B were mixed evenly in a volume ratio of 1:1, degassed, and spin-coated on a conductive substrate at a spin-coating speed of 500 rpm and a spin-coating time of 20 s. After spin-coating, the temperature was raised to 80°C and kept at a constant temperature for 15 minutes. During the heating and constant temperature keeping process, a corona electric field with an electric field strength of 15 kV / cm was continuously applied to prepare a flexible thin film layer with a micro-nano array structure.

[0056] (2) peeling the flexible film layer obtained in step (1) from the conductive substrate and treating it with oxygen plasma at a power of 80 W for 5 minutes;

[0057] (3) depositing a gold layer with a thickness of about 60 nm on the surface of the flexible thin film layer treated in step (2) by an ion beam sputtering process to prepare a second electrode layer;

[0058] (4) 1.5 g of the terpolymer P(VDF-TrFE-CTFE) powder was dissolved in 10 mL of N,N-dimethylformamide, and 1-ethyl-3-methylimidazole bis(trifluoromethylsulfonyl)imide was added at a mass ratio of 50% of P(VDF-TrFE-CTFE) to obtain a mixture, and the mixture was stirred until P(VDF-TrFE-CTFE) was completely dissolved to obtain a uniform solution;

[0059] (5) spin coating the uniform solution obtained in step (4) on the first electrode layer at a spin coating speed of 1000 rpm for 30 seconds, and then drying the spin-coated first electrode layer on a hot plate at 80° C. to completely evaporate the organic solvent, thereby preparing a flexible dielectric layer;

[0060] (6) The first electrode layer formed with the flexible dielectric layer and the flexible film layer formed with the second electrode layer are packaged, and electrode leads are drawn from the first electrode layer and the second electrode layer to obtain a sensor.

[0061] In the flexible capacitive sensor prepared in this embodiment, the thickness of the first electrode layer is 200 μm, and the thickness of the flexible dielectric layer is 15 μm.

[0062] The sensing performance of the flexible capacitive pressure sensors prepared in Examples 1 to 3 was tested. A universal testing machine was used to apply a load, and a Tonghui LCR impedance meter was used to measure the relative change in capacitance.

[0063] from Figure 2 It can be seen that the working principle of the flexible capacitive pressure sensor provided by the present invention is: after applying an external voltage, the electrons on the first electrode layer and the second electrode layer attract ions with opposite polarity in the flexible dielectric layer to gather at the interface between the electrode and the flexible electrolyte to form a double electric layer. A large number of electron-ion pairs at the interface are separated by nanometer distances, showing the characteristics of a micro / nano capacitor. When the microstructure electrode is deformed under pressure, the capacitance at the interface increases significantly due to the changing contact area between the second electrode layer and the ion layer under compression.

[0064] Figure 3This is the SEM image of the micro-nano array structure on the surface of the flexible film layer prepared in Example 1. It can be seen that the prepared micro-nano array structure is a regularly arranged concave-convex structure, which still presents a regular array arrangement at the hundred-micron level. The concave-convex structure is wavy in morphology, with a height of 92μm for the convex structure and a height of 8μm for the concave structure.

[0065] from Figure 4 It can be seen that the flexible capacitive pressure sensor prepared in Example 1 shows a sensitivity S=2.01 kPa at 50-200 kPa -1 , at 200-225kPa, sensitivity S = 27.07kPa -1 .

[0066] from Figure 5 It can be seen that the response time of the flexible capacitive pressure sensor prepared in Example 1 is 60 ms, and the recovery time is 80 ms.

[0067] from Figure 6 It can be seen that the detection limit of the flexible capacitive pressure sensor prepared in Example 1 can reach 100 mg.

[0068] from Figure 7 It can be seen that after the flexible capacitive pressure sensor prepared in Example 1 has undergone 2500 load cycles, the test results performance obtained is very different from the initial performance, and there is no obvious fluctuation as a whole. After amplifying the waveforms of the front-end cycle and the end of the later cycle, the similarity of the waveforms in the two compression stages can be seen, proving that it can guarantee stable sensing performance.

Claims

1. A flexible capacitive pressure sensor with a micro-nano array structure, characterized in that: The invention comprises a first electrode layer, a flexible dielectric layer, a second electrode layer and a flexible film layer which are stacked in sequence from top to bottom, and the flexible film layer has a micro-nano array structure.

2. The flexible capacitive pressure sensor according to claim 1, characterized in that: The micro-nano array structure is a regularly arranged concave-convex structure, the concave-convex structure is wavy in shape, the height of the convex structure is 90-100 μm, and the height of the concave structure is 5-10 μm.

3. The flexible capacitive pressure sensor according to claim 1, characterized in that: The material of the first electrode layer is PET / ITO conductive film, the material of the flexible dielectric layer is a mixture of terpolymer P (VDF-TrFE-CTFE) and 1-ethyl-3-methylimidazole bis(trifluoromethylsulfonyl)imide, the material of the second electrode layer is gold, and the material of the flexible film layer includes platinum catalyzed silica gel Ecoflex TM 00-30, one of polydimethylsiloxane PDMS.

4. The flexible capacitive pressure sensor according to claim 1, characterized in that: The thickness of the first electrode layer is 150-200 μm, the thickness of the flexible dielectric layer is 10-20 μm, and the thickness of the second electrode layer is 40-80 nm.

5. A method for preparing a flexible capacitive pressure sensor according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: (1) spin coating a material of a flexible film layer on a conductive substrate, and continuously applying a modulated corona electric field while heating and curing the material, so as to prepare a flexible film layer having a micro-nano array structure; (2) peeling the flexible film layer obtained in step (1) from the conductive substrate and subjecting it to oxygen plasma treatment; (3) depositing gold on the surface of the flexible thin film layer treated in step (2) by an ion beam sputtering process to prepare a second electrode layer; (4) dissolving the terpolymer P (VDF-TrFE-CTFE) powder in an organic solvent, and adding 1-ethyl-3-methylimidazole bis (trifluoromethylsulfonyl) imide to obtain a mixture, and stirring the mixture until the P (VDF-TrFE-CTFE) is completely dissolved to obtain a uniform solution; (5) spin coating the uniform solution obtained in step (4) on the first electrode layer, and then placing the first electrode layer after the spin coating solution on a hot plate to dry, so as to completely evaporate the organic solvent, thereby preparing a flexible dielectric layer; (6) Encapsulating a first electrode layer formed with a flexible dielectric layer and a flexible film layer formed with a second electrode layer, and extracting electrode leads from the first electrode layer and the second electrode layer to obtain the sensor.

6. The method for preparing the flexible capacitive pressure sensor according to claim 5, characterized in that: In step (1), the spin coating speed is 200 to 800 rpm, the spin coating time is 10 to 40 seconds, the temperature condition for the solution to be heated and solidified after spin coating is increased from room temperature to 70 to 90° C., the heating rate is 3° C. / min, and the temperature is maintained at a constant temperature for 10 to 20 minutes after reaching the set temperature. The electric field strength of the modulated corona electric field applied is 5 to 15 kV / cm.

7. The method for preparing the flexible capacitive pressure sensor according to claim 5, characterized in that: In step (2), the flexible film layer is treated with oxygen plasma at a power of 60 to 80 W for 2 to 5 minutes.

8. The method for preparing the flexible capacitive pressure sensor according to claim 5, characterized in that: In step (4), the amount of 1-ethyl-3-methylimidazole bis(trifluoromethylsulfonyl)imide added is 20% to 50% of the polyvinylidene fluoride based polymer powder, where the percentage is by mass.

9. The method for preparing the flexible capacitive pressure sensor according to claim 5, characterized in that: In step (5), the spin coating speed is 800-1200 rpm, the spin coating time is 20-50 s, and the hot plate temperature is set to 60-100°C.

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