Flexible multifunctional sensing film structure and preparation method thereof

Abstract

The invention belongs to the field of strain sensors, and particularly relates to a flexible multifunctional sensing film structure and a preparation method thereof. Two-dimensional material graphene is taken as a core, an ultrathin flexible extensible structure and a sensing unit for sensing strain, near-infrared light and temperature are designed and prepared, different parameter sensing function units are subjected to integrated design, and a first layer is a rigid substrate layer with a polished surface; the second layer is a sacrificial layer; the third layer is a flexible substrate layer; the fourth layer is a rigid base material layer; the fifth layer is a two-dimensional material; the sixth layer is an electrode; and the seventh layer is a near-infrared light sensing unit surface functional modification layer. The charge transfer compound is functionally modified on the surface of the graphene, so that the near-infrared light response sensitivity of the graphene is enhanced, and the overall design has flexibility, high sensitivity, multi-parameter independent sensing and good environmental adaptability.

Description

Technical Field

[0001] This invention belongs to the field of strain sensors, specifically relating to a flexible multifunctional sensing thin film structure and its preparation method. Background Technology

[0002] Electronic skin is a new type of flexible wearable sensor that can mimic or even surpass the sensory functions of the skin, converting sensory stimuli (strain, temperature, humidity, chemicals, etc.) into electrical information. Therefore, it is used in wearable devices, robots, human-machine interfaces, and prostheses.

[0003] As the human body's sensory system, skin contains numerous nerve endings that sense stimuli such as temperature and deformation. These nerve endings provide spatial distribution information on multiple parameters, including skin strain, temperature, and humidity, in response to external stimuli. Currently, research on electronic skin is still in its early stages, with most systems only capable of single-parameter sensing functions. Researchers are using polymers, carbon nanotubes, metal nanowires, and two-dimensional materials to achieve single-parameter sensing of temperature, pressure, light, or chemical substances. Compared to single-function sensing systems, multifunctional electronic skin integrating multiple sensors facilitates comprehensive monitoring of human health and the surrounding environment, has a wider range of applications, and can function similarly to human skin in fields such as prosthetics, robotics, and intelligent human-machine interfaces.

[0004] In recent years, researchers have proposed various methods for developing multifunctional electronic skin. Despite significant progress, many challenges remain in the research of stretchable multifunctional electronic skin. The multifunctional sensing capabilities of electronic skin are severely limited by the integration of sensing components. Achieving multifunctional sensing often comes at the cost of reduced sensitivity, making it difficult to simultaneously achieve multifunctional sensing and high sensitivity. Furthermore, the integration of different individual sensors complicates the structure and data acquisition, and the decoupling of different sensing signals often requires complex computations. Summary of the Invention

[0005] To address the aforementioned issues, this invention provides a flexible multifunctional sensing thin film structure and its fabrication method. Using two-dimensional material graphene as the core, this invention designs and fabricates an ultrathin, flexible, stretchable structure and sensing unit for sensing strain, near-infrared light, and temperature. Furthermore, it integrates different parameter sensing functional units and, through structural optimization design, obtains a stretchable thin film device with high sensitivity for multi-parameter sensing.

[0006] A method for fabricating a flexible multifunctional sensing thin film structure includes the following steps: (1) The first layer is a rigid base layer with a polished surface; (2) The second layer is a sacrificial layer: a water-soluble PVA polymer film is spin-coated on the surface of the polished rigid substrate and baked at 80°C for 10 minutes to obtain a PVA / rigid substrate; (3) The third layer is a flexible substrate layer: a PDMS flexible film is spin-coated on the surface of PVA / rigid substrate and baked at 70°C for 4 hours to completely cure it and obtain a PDMS flexible substrate. The PDMS flexible substrate is divided into three sensing unit regions from left to right: near-infrared light, temperature and strain, with a spacing of 200 μm. (4) The fourth layer is a rigid substrate layer: Al2O3 layer is prepared in the graphene near-infrared light and temperature sensing area by atomic layer deposition using the mask method to obtain Al2O3 / PDMS / PVA / rigid substrate, so as to decouple the effect of strain applied to the surface of PDMS flexible substrate on the near-infrared light and temperature sensing unit. (5) The fifth layer is a two-dimensional material: CVD-grown graphene on the surface of copper foil is transferred to the strain region of Al2O3 / PDMS / PVA / rigid substrate and PDMS flexible substrate, and the excess graphene region is etched by air plasma through a mask to obtain a block-shaped graphene sheet. (6) The sixth layer is an electrode: Two-end device electrodes are fabricated on the cubic graphene sheet in the strain sensing region by means of a mask to obtain a flexible sensor device for strain sensing; two-end device electrodes are fabricated on the cubic graphene sheet in the infrared sensing region to obtain a graphene near-infrared sensing unit; four-end device electrodes are fabricated on the cubic graphene sheet in the temperature sensing region, and defects are introduced by means of air plasma bombardment to obtain a flexible sensor device for temperature sensing. (7) The seventh layer is a functionalized modification layer on the surface of the near-infrared light sensing unit: a layer of charge transfer composite TTF+CA is deposited on the surface of the graphene near-infrared sensing unit in step (6) by dip-coating; finally, a flexible multifunctional thin film with multiple parameters of strain, near-infrared light and temperature sensing is prepared.

[0007] Preferably, the rigid substrate layer in step (1) is a 500 μm thick silicon / sapphire wafer.

[0008] Preferably, the thickness of the Al2O3 layer prepared in step (4) is 100 nm.

[0009] Preferably, the transfer method described in step (5) is PMMA polymer film-assisted transfer, specifically as follows: cut the copper foil with graphene grown on it into appropriately sized pieces and place them between two glass slides to flatten them; adsorb them onto the sample stage of a spin coater, and spin coat the surface of the copper foil with PMMA solution (solvent is ethyl lactate, molecular weight is 950K), then bake the copper foil with the PMMA film coated at 100°C for 10 minutes to allow the ethyl lactate solvent to completely evaporate; place the graphene / copper foil without the PMMA film coated on it with the side facing up, and bombard it with air plasma to etch away the graphene on the back of the copper foil; then place the PMMA film / graphene / copper foil at approximately 0.5... Soak the copper foil in a mol / L FeCl3 solution for more than 1 hour; after the copper foil is completely etched, clean it with deionized water containing hydrochloric acid and pure deionized water; take out the cleaned PMMA / graphene film, let it evaporate dry, and then attach it to the surface of the prepared PDMS / PVA / rigid substrate. Remove the PMMA polymer film from the surface of the obtained film by fumigation with hot acetone.

[0010] Preferably, in step (6), Ti and Au are sequentially prepared on a graphene sheet using thermal evaporation or electron beam evaporation.

[0011] More preferably, the Ti thickness prepared in step (6) is 10 nm and the Au thickness is 80 nm.

[0012] Preferably, the electrode strip in contact with the graphene in step (6) has a width of 30 μm, and the electrode strip is connected to a block electrode. The strain and near-infrared light sensing unit uses a two-end device with a distance of 150 μm between the two electrodes. The temperature sensing unit uses a four-electrode device with a distance of 30 μm between every two electrode strips.

[0013] The beneficial effects of this invention are: The rigid substrate layer, constructed using atomic layer deposition, effectively decouples strain from temperature and optical signals, reducing signal cross-interference in multi-parameter sensors and improving sensing accuracy and stability. Furthermore, functionalizing the graphene surface with charge transfer composites enhances the near-infrared light response sensitivity of graphene. The overall design combines flexibility, high sensitivity, independent multi-parameter sensing, and good environmental adaptability. Attached Figure Description

[0014] Figure 1 Multilayer structure design for graphene flexible electronic thin film unit devices; Figure 2 This is a top view of a graphene flexible electronic thin-film unit device. Figure 3 Schematic diagram of polymer film preparation by spin coating with a spin coater; Figure 4 A schematic diagram showing the CVD growth of graphene on copper foil assisted by PMMA polymer film transfer; Figure 5 This is a schematic diagram of the preparation of cubic graphene using a photomask. Figure 6 This is a schematic diagram of graphene device fabrication using a photomask method. Figure 7 The photoresponse of flexible electronic thin-film unit devices at a wavelength of 900 nm was measured.

[0015] Detailed Implementation Instructions The technical solutions of the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0016] Example 1 A method for preparing a flexible multifunctional sensing thin film: Multilayer structure of flexible electronic thin-film unit devices, such as Figure 1 As shown, top view (such as) Figure 2 The dimensions of each structure in the unit device are marked in the figure (shown), and are labeled with serial numbers ① to ⑦ respectively: ①, the first layer is a rigid substrate layer with a polished surface; ②, the second layer is a sacrificial layer; ③, the flexible substrate layer; ④, the rigid substrate layer; ⑤, the two-dimensional material; ⑥, the electrode; ⑦, the surface functionalization modification layer of the near-infrared light sensing unit.

[0017] (1) The first layer is a rigid base layer with a polished surface; (2) The second layer is a sacrificial layer: a water-soluble PVA polymer film (such as...) is spin-coated onto the surface of the polished rigid substrate layer (500 μm thick silicon wafer). Figure 3 (as shown), and baked on a hot plate at 80°C for 10 minutes to obtain a PVA / rigid substrate; (3) The third layer is a flexible substrate layer: a layer of PDMS flexible film is spin-coated on the surface of the PVA / rigid substrate and baked on a hot plate at 70°C for 4 hours to fully cure it; the PDMS flexible substrate is divided into three sensing unit regions from left to right: near-infrared light, temperature, and strain, with a spacing of 200 μm; the specific dimensions of each region are as follows Figure 2 As shown; (4) The fourth layer is a rigid substrate layer: A 100 nm thick Al2O3 layer is prepared in the graphene near-infrared light and temperature sensing area by atomic layer deposition using the mask method to obtain Al2O3 / PDMS / PVA / rigid substrate, so as to decouple the effect of strain applied to the surface of PDMS flexible substrate on the near-infrared light and temperature sensing unit. (5) The fifth layer is a two-dimensional material: Graphene grown by CVD on the surface of copper foil (Graphene Research Institute) is transferred to the strain region of Al2O3 / PDMS / PVA / rigid substrate and PDMS flexible substrate using a PMMA polymer film-assisted transfer method (e.g. Figure 4 As shown in the diagram, the specific steps are as follows: Cut the copper foil with graphene grown on it into appropriately sized pieces and flatten them between two glass slides; place them on the sample stage of a spin coater, and spin coat the surface of the copper foil with PMMA solution (ethyl lactate solvent, molecular weight 950K). Then, place the copper foil with the PMMA film on a hot plate at 100°C and bake for 10 minutes to allow the ethyl lactate solvent to evaporate completely; place the graphene / copper foil without the PMMA film on the side facing up and bombard it with air plasma to etch away the graphene on the back of the copper foil; then place the PMMA film / graphene / copper foil in an approximately 0.5 mol / L... The copper foil was soaked in FeCl3 solution for more than 1 hour; after it was completely etched, it was washed with deionized water containing hydrochloric acid and pure deionized water; the cleaned PMMA / graphene film was taken out and allowed to evaporate, then it was attached to the surface of the prepared PDMS / PVA / rigid substrate. The obtained sheet was then fumigated with hot acetone to remove the PMMA polymer film on the surface; a CVD-grown graphene film was transferred onto the surface of the Al2O3 / PDMS / PVA / rigid substrate, and the excess graphene area was etched with air plasma using a mask method to obtain cubic graphene sheets for the preparation of graphene near-infrared light sensing units (e.g., Figure 5 (as shown) (6) The sixth layer is the electrode: Two-terminal device electrodes are fabricated on the cubic graphene sheet in the strain sensing region using a mask method to obtain a flexible strain sensing sensor; two-terminal device electrodes are fabricated on the cubic graphene sheet in the infrared sensing region to obtain a graphene near-infrared sensing unit; four-terminal device electrodes are fabricated on the cubic graphene sheet in the temperature sensing region, and defects are introduced by air plasma bombardment to obtain a flexible temperature sensing sensor; the electrodes are fabricated on the graphene sheet using thermal evaporation or electron beam evaporation methods to sequentially prepare 10 nm Ti and 80 nm Au (e.g., ...) Figure 6 (As shown); the electrode strip in contact with the graphene is 30 μm wide, and the electrode strip is connected to a block electrode. The strain and near-infrared light sensing unit uses a two-end device with a distance of 150 μm between the two electrodes. The temperature sensing unit uses a four-electrode device with a distance of 30 μm between every two electrode strips. (7) The seventh layer is a functional modification layer on the surface of the near-infrared light sensing unit: a charge transfer composite TTF+CA is deposited on the surface of the graphene near-infrared sensing unit by dip-coating method; finally, a flexible multifunctional thin film with multiple parameters of strain, near-infrared light and temperature sensing is prepared.

[0018] Experimental Example 1 Light response test: Using the EXR-4 supercontinuum light source laser outlet, a 500-2400 nm supercontinuum laser was emitted to test the near-infrared light sensing performance of the flexible multifunctional electronic thin film obtained in Example 1.

[0019] like Figure 7 The photoresponse test results of the sample at a wavelength of 900 nm are shown. From the I-time characteristic curves (Vds=0.3 V) for different laser powers, it can be seen that the light intensity is 69 μW / mm. 2 123 μW / mm 2 156 μW / mm 2 and 174 μW / mm 2 At these times, the photocurrents of the samples were 0.02 nA, 0.05 nA, 0.09 nA, and 0.104 nA, respectively. According to the criterion for minimum perceptible light intensity, at a light intensity of 123 μW / mm², the minimum perceptible light intensity is [not specified]. 2 At that time, the average photocurrent (0.05 nA) was more than twice the measured current noise (0.018 nA). Therefore, at a wavelength of 900 nm, the sensing light intensity of the flexible electronic thin-film unit device can reach 123 μW / mm². 2 .

Claims

1. A method for preparing a flexible multifunctional sensing film structure, characterized in that, The method comprises the following steps: (1) the first layer is a surface-polished rigid substrate layer; (2) the second layer is a sacrificial layer: spin-coating a water-soluble PVA polymer film on the surface of the polished rigid substrate layer, baking at 80 DEG C for 10 minutes to obtain a PVA / rigid substrate; (3) the third layer is a flexible substrate layer: spin-coating a PDMS flexible film on the surface of the PVA / rigid substrate, baking to obtain a PDMS flexible substrate, and dividing the PDMS flexible substrate into three sensing unit regions of near-infrared light, temperature and strain from left to right with a spacing of 200 μm; (4) the fourth layer is a rigid substrate layer: using a mask plate method, an Al2O3 layer is prepared in the graphene near-infrared light and temperature sensing region by atomic layer deposition to obtain an Al2O3 / PDMS / PVA / rigid substrate; (5) the fifth layer is a two-dimensional material: the graphene grown on the surface of a copper foil by CVD is transferred to the Al2O3 / PDMS / PVA / rigid substrate and the strain region of the PDMS flexible substrate, and the excess graphene region is etched by air plasma through a mask plate to obtain a square graphene sheet; (6) the sixth layer is an electrode: two-terminal device electrodes are prepared on the square graphene sheet in the strain sensing region by a mask plate method to obtain a flexible sensor device for strain sensing; two-terminal device electrodes are prepared on the square graphene sheet in the infrared sensing region to obtain a graphene near-infrared sensing unit; four-terminal device electrodes are prepared on the square graphene sheet in the temperature sensing region, and defects are introduced by air plasma bombardment to obtain a flexible sensor device for temperature sensing; (7) the seventh layer is a surface functionalization modification layer of the near-infrared light sensing unit: a layer of charge transfer complex TTF+CA is deposited on the surface of the graphene near-infrared sensing unit in step (6) by immersion and pulling method; finally, a flexible multifunctional film for strain, near-infrared light and temperature multi-parameter sensing is prepared.

2. The production method according to claim 1, characterized by, The rigid substrate layer in step (1) is a 500 μm thick silicon / sapphire wafer.

3. The production method according to claim 1, characterized by, The baking time in step (3) is 4 hours, and the baking temperature is 70 DEG C.

4. The production method according to claim 1, characterized by, The thickness of the Al2O3 layer prepared in step (4) is 100 nm.

5. The production method according to claim 1, characterized by, The transferring method in the step (5) is PMMA polymer film assisted transferring, and the specific steps are as follows: the copper foil with graphene grown thereon is cut into a block with a proper size, and is placed between two glass slides and flattened; the copper foil is adsorbed on a sample table of a spin coater, and PMMA solution is dropped on the surface of the copper foil and spin coated, then the copper foil with the spin-coated PMMA film is baked for 10 minutes to make the ethyl lactate solvent completely volatilize; the graphene / copper foil without the spin-coated PMMA film is placed with the graphene facing upward, and the graphene on the back of the copper foil is etched by air plasma; then the PMMA film / graphene / copper foil is immersed in a FeCl3 solution with a concentration of about 0.5 mol / L for more than 1 hour; after the copper foil is completely etched, the copper foil is cleaned with deionized water with hydrochloric acid dropped thereinto and pure deionized water; the cleaned PMMA / graphene film is taken out, and after the water volatilizes, the PMMA / graphene film is attached to the surface of the prepared PDMS / PVA / rigid substrate, and the obtained sheet is fumigated with hot acetone to remove the PMMA polymer film on the surface.

6. The preparation method according to claim 5, characterized in that, The temperature of the copper foil with the spin-coated PMMA film in the step (5) is 100℃ during baking.

7. The preparation method according to claim 1, characterized in that, The electrodes in the step (6) are prepared on the graphene sheet by a method of thermal evaporation or electron beam evaporation in sequence of Ti and Au.

8. The production method according to claim 7, characterized by, The thickness of Ti in the step (6) is 10 nm, and the thickness of Au is 80 nm.

9. The production method according to claim 1, characterized by, The width of the electrode strip in contact with the graphene in the step (6) is 30 μm, and the square electrode block connected with the electrode strip is a two-terminal device, the distance between the two electrodes is 150 μm, the temperature sensing unit is a four-terminal device, and the distance between every two electrode strips is 30 μm.

10. A flexible multifunctional sensing film structure prepared by the method according to any one of claims 1-9.

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