Preparation technology of micro-nano conformal sensing amorphous carbon film piezoresistive sensor and amorphous carbon film piezoresistive sensor

Abstract

The present invention relates to the technical field of piezoresistive sensors, and specifically to a micro-nano conformal sensing amorphous carbon film piezoresistive sensor preparation process and an amorphous carbon film piezoresistive sensor. The micro-nano conformal sensing amorphous carbon film piezoresistive sensor preparation process includes obtaining a three-dimensional model of a target curved surface, mapping the three-dimensional model to a flat screen printing mold respectively; preparing a sensing slurry and pre-treating the sensing slurry; preparing a substrate and optimizing the substrate through a micro-nano preparation process; and using a flat screen printing mold to print the pre-treated sensing slurry to the optimized substrate to form an amorphous carbon film sensing layer. The purpose is to achieve conformal sensing of curved surface pressure and improve the performance stability of the piezoresistive sensor.

Description

Technical Field

[0001] The present invention relates to the technical field of piezoresistive sensors, and in particular to a preparation process for a micro-nano conformal sensing amorphous carbon film piezoresistive sensor and an amorphous carbon film piezoresistive sensor. Background Art

[0002] Piezoresistive sensor is a device that can convert mechanical pressure into electrical signal output. It is widely used in various fields, including but not limited to health monitoring, smart wearable devices, industrial automation and automotive engineering.

[0003] At present, the common methods for preparing piezoresistive sensors in the prior art are:

[0004] The stacked structure is usually composed of multiple layers of materials with different functions, such as a flexible polymer layer, a metal electrode layer, a carbon nanotube film electrode layer, a photoresist insulating layer, etc.

[0005] Composite materials combined with carbon nanotube dispersions. This method takes advantage of the good conductivity and high mechanical strength of carbon nanotubes and evenly disperses them in a flexible matrix to form a composite material.

[0006] Linear polymers based on hybrid graphene: By mixing graphene with polymers, a composite material with excellent mechanical and conductive properties is formed, which is then woven into a linear structure with good flexibility and wear resistance, suitable for applications that require bending and stretching;

[0007] The design of the above-mentioned existing piezoresistive sensors is usually only applicable to planar scenarios. Even if a flexible substrate is used, when the planar sensor is directly attached to a curved surface, the deformation of the material will affect the sensor signal acquisition quality and the sensor's working performance. On the other hand, whether it is multi-layer stacking or the preparation of composite materials, the manufacturing process is relatively complicated and requires precise control of the conditions of each step, which not only increases the manufacturing cost but also reduces production efficiency. Summary of the invention

[0008] In order to realize the conformal sensing of curved surface pressure and improve the performance stability of piezoresistive sensors, the present invention provides a micro-nano conformal sensing amorphous carbon film piezoresistive sensor preparation process and an amorphous carbon film piezoresistive sensor. The technical solutions adopted are as follows:

[0009] The first technical solution of the present invention provides a preparation process for a micro-nano conformal sensing amorphous carbon film piezoresistive sensor, the preparation process comprising:

[0010] Obtain a three-dimensional model of the target surface, and map the three-dimensional model to a flat screen printing mold;

[0011] preparing a sensing slurry and pretreating the sensing slurry;

[0012] Prepare a substrate and optimize the substrate through micro-nano preparation technology;

[0013] The pre-treated sensing slurry is printed onto the optimized substrate using a flat screen printing mold to form an amorphous carbon film sensing layer.

[0014] Further, obtaining a three-dimensional model of the target surface and mapping the three-dimensional model to a planar flexible substrate includes:

[0015] Mapping a 3D model to a flat flexible substrate based on a surface unfolding algorithm, including:

[0016] Obtaining 3D point cloud data of the target surface and constructing a 3D surface model;

[0017] Perform edge detection on the three-dimensional surface model and extract the edge with the maximum curvature gradient;

[0018] The three-dimensional surface model is mapped to a plane using conformal mapping to obtain a plane unfolding image, and the plane unfolding image is processed to minimize distortion and wrinkles.

[0019] Further, preparing the sensing slurry and pre-treating the sensing slurry comprises:

[0020] The sensing paste is formed by graphene nanosheets, multi-walled carbon nanotubes and conductive ink to form a composite sensing paste.

[0021] Furthermore, the ratio of graphene nanosheets, multi-walled carbon nanotubes and conductive ink in the composite sensing slurry is 1:1:8.

[0022] Further, preparing the sensing slurry and pre-treating the sensing slurry further comprises:

[0023] Ultrasonic atomization treatment is performed on the composite sensing slurry;

[0024] The composite sensing slurry after ultrasonic atomization treatment is magnetically stirred.

[0025] Furthermore, a substrate is prepared and optimized by a micro-nano preparation process, including:

[0026] Prepare a substrate by spin coating and curing process and cut the substrate;

[0027] The substrate surface is treated with oxygen plasma.

[0028] Furthermore, the method further comprises: performing photolithography patterning treatment on the substrate after the oxygen plasma treatment.

[0029] Furthermore, the method also includes: preparing an electrode on the substrate that has been subjected to photolithography patterning processing by using magnetron sputtering.

[0030] Further, the pre-treated sensing slurry is printed onto the optimized substrate using a silk screen mold to form an amorphous carbon film sensing layer, which includes:

[0031] performing stress relief annealing on the substrate;

[0032] Performing square resistance test and piezoresistance test on the substrate after stress relief annealing;

[0033] Restore the amorphous carbon film piezoresistive sensor to the target surface.

[0034] The second technical solution of the present invention provides a micro-nano conformal sensing amorphous carbon film piezoresistive sensor, which adopts the micro-nano conformal sensing amorphous carbon film piezoresistive sensor preparation process described in the first technical solution of the present invention. The amorphous carbon film piezoresistive sensor includes a substrate layer and an amorphous carbon film sensing layer, a microstructure layer and a lead layer arranged on the substrate layer; the amorphous carbon film sensing layer is configured to be printed on the substrate using a screen printing process, and is used to sense pressure changes and convert them into electrical signal output; the microstructure layer is configured to be arranged between the amorphous carbon film sensing layer and the substrate using a micro-nano preparation process, and is used to form a graphic microstructure of the amorphous carbon film piezoresistive sensor; the lead layer is arranged on the top of the substrate, and is used to electrically connect the amorphous carbon film sensing layer with an external circuit.

[0035] The present invention has the following beneficial effects:

[0036] The micro-nano conformal sensing amorphous carbon film piezoresistive sensor preparation process and the amorphous carbon film piezoresistive sensor provided by the present invention optimize the substrate surface through the micro-nano preparation process, and use a flat screen printing mold to print the pretreated sensing slurry onto the optimized substrate to form an amorphous carbon film sensing layer, which effectively combines screen printing and micro-nano preparation processes, giving full play to the advantages of screen printing in efficient production while taking into account the advantages of micro-nano preparation in ensuring the quality of the amorphous carbon film sensing layer. The softness and high sensitivity of the amorphous carbon film enable the sensor to maintain good fit in a complex curved environment, thereby realizing accurate measurement of curved surface pressure. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions and advantages in the embodiments of the present invention or the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0038] Figure 1 A flow chart of a method for preparing an amorphous carbon film piezoresistive sensor provided by one embodiment of the present invention;

[0039] Figure 2A schematic diagram of a surface conformal sensing planarization process provided by an embodiment of the present invention;

[0040] Figure 3 A schematic diagram of a foot surface conformal sensing planarization process provided by an embodiment of the present invention;

[0041] Figure 4 A schematic cross-sectional view of an amorphous carbon film piezoresistive sensor provided by one embodiment of the present invention;

[0042] Figure 5 An axonometric diagram of an amorphous carbon film piezoresistive sensor provided by one embodiment of the present invention;

[0043] Figure 6 A top view of an amorphous carbon film piezoresistive sensor provided by one embodiment of the present invention;

[0044] Icon: 100-base layer, 200-amorphous carbon film sensing layer, 300-microstructure layer, 400-lead layer. DETAILED DESCRIPTION

[0045] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following is a detailed description of the preparation process of a micro-nano conformal sensing amorphous carbon film piezoresistive sensor and an amorphous carbon film piezoresistive sensor proposed by the present invention, its specific implementation method, structure, characteristics and effects, in combination with the accompanying drawings and preferred embodiments. In the following description, different "one embodiment" or "another embodiment" does not necessarily refer to the same embodiment. In addition, specific features, structures or characteristics in one or more embodiments may be combined in any suitable form.

[0046] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0047] The following is a detailed description of a micro-nano conformal sensing amorphous carbon film piezoresistive sensor preparation process and a specific scheme of an amorphous carbon film piezoresistive sensor provided by the present invention in conjunction with the accompanying drawings. The working principle of the amorphous carbon film piezoresistive sensor is based on the piezoresistive effect. When the sensor is subjected to an external force, the amorphous carbon film will deform, causing its resistance to change. This change in resistance can be measured by a circuit connected to the sensor and converted into a useful signal, such as a change in voltage or current. By analyzing these signals, information about the magnitude of the pressure can be obtained;

[0048] See also Figure 1 , which shows a flow chart of a method for preparing a micro-nano conformal sensing amorphous carbon film piezoresistive sensor according to an embodiment of the present invention, wherein the preparation process comprises:

[0049] Step S100: Obtain a three-dimensional model of the target surface, and map the three-dimensional model to a flat screen printing mold; for details, please refer to Figure 2 ,against Figure 2 (a) The outer surface perception of the three-dimensional structure of the platform, in this embodiment, the three-dimensional structure of the platform is unfolded into Figure 2 (b) is formed on the plane shown in the figure, and then plane patterning, etching, coating and other processes are performed to realize the preparation of the sensor; after the sensor preparation is completed, the entire sensor can be pasted back to the three-dimensional structure of the platform; specifically, a 3D scanner can be used to scan the outer surface of the target object to obtain a three-dimensional model of the target surface, and then the flattening function in the CREO software is used to convert the three-dimensional model into a two-dimensional plane layout diagram, and finally the drawing is exported, and the silk screen mold is designed in combination with the drawing; the mesh number of the plane silk screen mold is selected to be 240-430, and the preferred mesh number is 300;

[0050] Step S100 specifically includes:

[0051] Step S110: mapping the three-dimensional model to a planar flexible substrate based on a surface unfolding algorithm, including:

[0052] Step S120: Acquire the three-dimensional point cloud data of the target surface and construct a three-dimensional surface model;

[0053] Step S130: perform edge detection on the three-dimensional surface model and extract the edge with the maximum curvature gradient; specifically, use the Gaussian curvature algorithm to calculate the curvature of each vertex on the three-dimensional surface model, and extract the edge with the maximum curvature gradient by comparing the curvature difference between adjacent vertices. The expression is:

[0054]

[0055] In the formula, Indicates Gaussian curvature within the area of ​​vertices; Indicates The area of ​​the domain of the vertices; Indicates A vertex and its neighboring vertices The angle formed; Indicates the number of vertices;

[0056]

[0057] Indicates The vertices and The curvature difference between the vertices is calculated; specifically, the edge with the maximum curvature gradient is considered to be the "steepest" edge; by extracting the edge with the maximum curvature gradient, the most significant feature edges on the target surface can be identified, and these edges can be used as dividing lines in the unfolding process, which helps to reduce distortion and wrinkles in the unfolding process; on the other hand, clear dividing lines can also simplify the subsequent screen printing process steps, making the manufacturing process of the piezoresistive sensor more efficient and controllable; through the operation of step S130, the key edges on the three-dimensional surface model can be effectively identified and used as reference lines or dividing lines in the subsequent unfolding process, thereby improving the manufacturing accuracy and performance of the sensor. This process not only helps to reduce distortion and wrinkles, but also ensures the application effect of the sensor on complex surfaces.

[0058] Step S140: Use conformal mapping to map the three-dimensional surface model to a plane, obtain a plane unfolding diagram, and minimize distortion and wrinkles on the plane unfolding diagram; specifically, use an angle-preserving mapping method to map the three-dimensional surface model to a two-dimensional plane, and its goal is to keep the local angle unchanged during the mapping process; use a numerical method to solve the conformal mapping equation, project the three-dimensional surface onto the two-dimensional plane, and generate a plane unfolding diagram of the foot; in the mapping process, adjust parameters and optimize algorithms to minimize distortion and wrinkles, and use Laplace energy minimization to optimize the plane diagram, and its expression is:

[0059]

[0060] In the formula, Represents a three-dimensional surface Mapping function to a two-dimensional plane; Represents the gradient of the mapping function; Represents the area elements on the surface; specifically includes:

[0061] Initialization: determine the initial state of the 3D surface model and set boundary conditions;

[0062] Discretization: Discretize the three-dimensional surface model into a grid, where each grid node represents a vertex;

[0063] Energy Function: Define the energy function Measures the degree of distortion of the mapped plan;

[0064] Optimization algorithm: Use iterative optimization algorithms such as gradient descent and conjugate gradient method to gradually optimize the mapping function , so that the energy function Reach a minimum value;

[0065] Iterative update: Update the mapping function through iteration , after each iteration, check the energy function Whether it decreases until convergence or the predetermined number of iterations is reached;

[0066] Distortion minimization is to add the Laplace energy term to the energy function to ensure that the distortion of the area and shape of the mapped plane image is minimized under the premise that the local angle remains unchanged; by adjusting the weight coefficient in the energy function, the Laplace energy and other energy terms are balanced to make the mapping result closer to the geometric characteristics of the original surface;

[0067] The wrinkle processing is specifically as follows: in the mapping process, the behavior of the mapping function is restricted by boundary constraints to ensure that the points on the boundary are mapped to the plane in a predetermined manner; the mapping function is gradually adjusted using a relaxation processing method so that each part of the surface can be smoothly mapped to the plane to reduce the generation of wrinkles; in the optimization process, the mapping results are continuously checked, and once wrinkles are found, the wrinkles are reduced or eliminated by adjusting the boundary conditions or the optimization algorithm; the boundary conditions can be selected and adjusted according to actual needs; through the operation of step S140, we can effectively map the three-dimensional surface model to the two-dimensional plane and generate a high-quality plane unfolding diagram, thereby providing an accurate template for the subsequent manufacture of amorphous carbon film piezoresistive sensors;

[0068] The following is a specific implementation method using the human foot as an example: Specifically, the preparation process can be applied to various curved surface pressure monitoring scenarios. This embodiment takes the human foot as an example. During the plantar pressure test, pressure monitoring of the side of the foot, the dorsum of the foot, and other areas is required; please refer to Figure 3 In this embodiment, the human foot is taken as an example. Figure 3 (a) is a three-dimensional image of the human foot. Figure 3 (b) is a planar unfolded view of the foot, which will be the basis for screen printing in the subsequent manufacturing process. Similar smart socks can be prepared based on this preparation method to capture the pressure values ​​of various points of the entire foot during movement in real time, which can be used as a reference for clinicians. Based on the above-mentioned surface conformal sensing planarization processing process, the pressure perception of the foot can be extended to the entire foot, rather than conventional plantar pressure monitoring. The sensing surface of the entire foot can be unfolded into Figure 3After the piezoresistive sensors are prepared in the four areas shown in (b), they are glued back to the curved surface, for example, fixed on the outside of the socks or the inside of the shoes, so as to realize omnidirectional sensing of the foot; the whole is composed of multiple single-point amorphous carbon film piezoresistive sensors connected by flexible wires to realize signal conduction; when the curved surface is unfolded into a plane, conventional preparation processes can be used to realize the preparation of routing, sensing layer, packaging layer, etc.; this embodiment uses the angle-preserving mapping method to keep the local angle unchanged during the mapping process, thereby better retaining the geometric features of the original surface and ensuring the accuracy and reliability of the unfolded image; through the Laplace energy minimization and optimization algorithm, the distortion and wrinkles in the mapping process can be effectively reduced, making the plane unfolded image smoother, which is beneficial to the subsequent manufacturing process; the optimized plane unfolded image can be used as a template for screen printing to ensure that the amorphous carbon film sensing layer is more evenly distributed on the substrate and improve the manufacturing accuracy of the sensor.

[0069] It should be noted that the preparation process of the micro-nano conformal sensing amorphous carbon film piezoresistive sensor is not limited to the above-mentioned application scenarios, but can also be expanded to human facial perception, legs, joints, and seat cushions. Further miniaturization can also realize bone surface tension monitoring. Its main principle is similar to the above-mentioned process, which uses the method of unfolding the three-dimensional surface into a plane and combining micro-nano conformal sensing amorphous carbon film silk-screen printing and micro-nano preparation composite process to realize sensor preparation.

[0070] Step S200: preparing a sensing slurry and pretreating the sensing slurry; specifically, the sensing slurry uses graphene nanosheets, multi-walled carbon nanotubes and conductive ink to form a composite sensing slurry; the purity of the graphene nanosheets is preferably 99%, the layer thickness is preferably 1.2nm, the diameter is preferably 1.5um, and the number of layers per sheet does not exceed 5; the purity of the multi-walled carbon nanotubes is more than 99%, the inner diameter is preferably 3-6nm, the outer diameter is preferably 7-12nm, the length is preferably 7-13um, and the resistivity is preferably 600-1100 micro-ohm meters; the square resistance of the conductive ink is preferably 4000K square resistance; the ratio of graphene nanosheets, multi-walled carbon nanotubes and conductive ink is 1:1:8; high-purity graphene nanosheets and multi-walled carbon nanotubes are selected, and their sizes and proportions are optimized to improve the conductivity of the sensing slurry, thereby improving the sensitivity and response speed of the piezoresistive sensor;

[0071] Step S200 specifically includes:

[0072] Step S210: ultrasonically atomize the composite sensing slurry; specifically, an ultrasonic processor of model PS-80 and an ultrasonic atomization system of model UAM4000 are preferably used, and the composite sensing slurry is poured into an ultrasonic atomization container. The power of the ultrasonic atomization equipment is preferably 200W, and the processing time is preferably 120 minutes; the ultrasonic wave will produce a cavitation effect in the composite sensing slurry, that is, tiny bubbles are formed inside the composite sensing slurry and a large amount of energy is released in the subsequent collapse process, so that the particles in the composite sensing slurry are dispersed more evenly; ultrasonic atomization treatment can effectively break the agglomeration of graphene nanosheets and multi-walled carbon nanotubes, so that these nanomaterials are more evenly distributed in the conductive ink matrix, and the evenly dispersed slurry can be more evenly spread on the substrate during screen printing to form an amorphous carbon film layer with uniform thickness, thereby improving the conductivity and mechanical stability of the amorphous carbon film finally produced;

[0073] Step S220: magnetically stirring the composite sensing slurry after ultrasonic atomization treatment; specifically, the magnetic stirrer is preferably a Proko Instrument of model MS3-4, preparing the composite sensing slurry after ultrasonic atomization treatment and transferring it to the container of the magnetic stirrer, the speed of the magnetic stirrer is preferably 800 revolutions per minute, and the processing time is preferably 3 hours; after the magnetic stirring treatment, the dispersion effect of the slurry after ultrasonic atomization can be further improved, ensuring that the graphene nanosheets, multi-walled carbon nanotubes and conductive ink are evenly distributed in the slurry, improving the printing quality, and combined with the subsequent UV curing and stress relief annealing process, magnetic stirring can effectively reduce the stress concentration in the amorphous carbon film, thereby reducing the occurrence of cracks, so that the sensor still maintains good mechanical properties during repeated use, so that the final supported sensor can still have good film quality and signal perception ability when it is back attached to the curved surface;

[0074] Step S300: preparing a substrate and optimizing the substrate through a micro-nano preparation process; specifically, the substrate is the basis of the sensor structure and is used to provide physical support for the amorphous carbon film layer and other functional layers. The selection of the substrate material needs to have a certain degree of flexibility so that the quality of the film layer can be maintained during the process of back-pasting from a flat surface to a curved surface;

[0075] Step S300 specifically includes:

[0076] Step S310: Prepare a substrate by spin coating and curing process and cut the substrate; specifically, use polydimethylsiloxane (PDMS), preferably Dow Corning DC184 as the flexible substrate material, and the ratio of the main liquid to the auxiliary liquid is preferably 10:1; mix the main liquid and the auxiliary liquid in a ratio of 10:1 to ensure that the two liquids are fully mixed to avoid the phenomenon of uneven mixing; drop the mixed PDMS solution onto the pre-cleaned substrate material, and use a spin coater to perform spin coating, the speed is preferably 4000 revolutions per minute, the time is preferably 70 seconds, and the high-speed rotation of the spin coater can be The PDMS solution is allowed to form a uniform thin film on the substrate; after the spin coating is completed, the substrate with the PDMS thin film is placed in an oven for curing. The curing temperature is preferably 120 degrees Celsius and the curing time is preferably 60 minutes. High-temperature curing can accelerate the cross-linking reaction of PDMS and form a stable polymer network; after the curing is completed, the substrate is allowed to cool naturally to room temperature and the cured PDMS substrate can be cut into the required size and shape according to the design requirements; through the spin coating process, a uniform PDMS film with controllable thickness can be obtained, which can ensure that the sensor has similar performance in different areas;

[0077] Step S320: using oxygen plasma to treat the surface of the substrate; specifically, the model of the plasma treatment equipment is preferably JR-2B, which can generate plasma for surface modification, including the following steps: placing the prepared PDMS substrate in the chamber of the plasma treatment equipment; closing the chamber door, starting the vacuum pump, and reducing the pressure in the chamber to a set 5E-3Pa; opening the oxygen valve and adjusting the flow rate to 240ml / min; turning on the power, setting the power to 580W, and starting the plasma generator; the plasma treatment equipment lasts for 6 minutes, during which all parameters are ensured to be stable; after the treatment is completed, turning off the power and the oxygen valve, slowly venting, so that the pressure in the chamber returns to atmospheric pressure; taking the treated substrate out of the chamber and preparing for the next step; in this embodiment, oxygen plasma treatment can introduce polar groups (such as hydroxyl and carboxyl) to the surface of the PDMS substrate, thereby increasing its surface energy and enhancing wettability; plasma treatment can also remove organic pollutants and oxides on the surface of the substrate, exposing more active sites, thereby enhancing the interfacial bonding between the amorphous carbon film and the PDMS substrate, and improving the overall performance of the sensor;

[0078] Step S330: performing photolithography patterning on the substrate after oxygen plasma treatment; specifically, the photoresist is preferably AZ5214, and the photoresist is evenly spin-coated on the PDMS substrate after oxygen plasma treatment, and the spin coating parameters are preferably 7000 revolutions per minute for 60 seconds; the purpose is to form a uniform photoresist film on the substrate;

[0079] After the spin coating is completed, the substrate coated with the photoresist is placed in an oven for pre-baking treatment, the pre-baking temperature is preferably 110 degrees Celsius, and the time is preferably 70 seconds; the MICROLAB laser direct writing equipment is used for photolithography patterning, the exposure time is preferably 30 microseconds (μ, the cut width is preferably 256 pixels, the number of overlaps is preferably 4 times, and the spot diameter is preferably 200 microns; laser direct writing lithography is a technology that can directly draw patterns on photoresist without a mask; after the exposure is completed, the substrate is placed in a developer for development treatment; through laser direct writing lithography technology, the size of 200 microns and above of traditional hard mask coating technology can be increased to micro-nano structures of 500 nanometers to 10 microns; this high-resolution patterning technology enables the sensor surface to have a more delicate microstructure, thereby improving the sensor's perception of subtle pressure changes; the presence of micro-nano structures enables the sensor to produce significant resistance changes under small pressure changes, thereby reducing the detection limit, which is suitable for application scenarios requiring high-sensitivity detection.

[0080] Step S340: using magnetron sputtering to prepare an electrode on a substrate that has been subjected to photolithography patterning; specifically, the model of the magnetron sputtering equipment is preferably MSP-300BI, and the process is as follows: placing the substrate that has been subjected to photolithography patterning into the chamber of the magnetron sputtering equipment, the magnetron sputtering power is preferably 100 watts, the thickness of the deposited film is preferably 1.5 microns, and the deviation does not exceed 2%; evacuating to a preset background vacuum of the equipment; loading a target material (usually a metal target material, such as gold, silver, copper, etc.), and adjusting the flow rate of a corresponding gas (such as argon) to maintain a stable plasma environment; starting a 120-second pre-sputtering to clean the surface of the target material; after the pre-sputtering is completed, turning on the sputtering power supply, the power is preferably 100 watts, and starting the formal sputtering process. During the sputtering process, the substrate temperature is maintained at 50 degrees Celsius, and the sputtering time is monitored to ensure that the sputtering time is 60 minutes; after the sputtering is completed, turning off the power supply, gradually restoring the pressure in the chamber to atmospheric pressure, and taking out the substrate on which the electrode film is deposited;

[0081] This embodiment can provide a uniform and dense electrode film through magnetron sputtering technology, which helps to improve the contact performance between the electrode and the amorphous carbon film sensing layer, thereby improving the overall performance of the sensor; by precisely controlling the sputtering conditions, it is ensured that the adhesion between the electrode film and the substrate is stronger, reducing the risk of the electrode falling off during use; strictly controlling parameters such as power, time and substrate temperature during the sputtering process can achieve a high degree of uniformity in the film thickness, ensuring that the electrical performance of the sensor is stable and reliable, and high-quality electrodes can reduce contact resistance, thereby improving the sensitivity of the sensor to pressure changes. In addition, a uniform electrode film helps to achieve more accurate pressure signal transmission.

[0082] In summary, in step S300, the functional groups introduced by oxygen plasma treatment and the optimized film sputtering process can significantly improve the bonding force between the film layer and the substrate and reduce the risk of delamination and peeling; the optimized sputtering conditions can improve the microstructure of the amorphous carbon film, making it have a higher density and flatness, thereby improving its electrical and mechanical properties. Through the above treatment, the microstructure of the amorphous carbon film is optimized, and its conductive network is more uniform, thereby improving the response speed and sensitivity of the sensor to pressure changes.

[0083] Step S400: using a screen printing mold to print the pretreated sensing slurry onto the optimized substrate to form an amorphous carbon film sensing layer; specifically, the model of the printing equipment is preferably TY-CP2530bs-ccd, the number of printings is preferably 5 times, the interval between each printing is preferably 20 seconds, and the printing speed is preferably 0.5 m / s; placing the optimized PDMS substrate on the workbench of the screen printer; evenly applying the pretreated sensing slurry on the screen printing mold; starting the screen printer and printing according to the set parameters to ensure that the mold and the substrate are in close contact to avoid missing printing or uneven printing; after completing one printing, wait 20 seconds to allow the slurry to solidify, and then proceed to the next printing, and repeat this process until 5 printings are completed; through the screen printing process of step S400, we can accurately print the pretreated sensing slurry onto the optimized substrate according to a predetermined pattern to form a uniform and dense amorphous carbon film sensing layer;

[0084] After step S400, the following steps are also included:

[0085] Step S410: performing stress relief annealing on the substrate; specifically, placing the printed substrate in an oven, heating the oven to 120 degrees Celsius, and maintaining the temperature for 30 minutes; naturally cooling to room temperature for 30 minutes; repeating the above steps for a total of 5 cycles; during the entire process, the oven is kept filled with nitrogen to prevent oxygen in the air from oxidizing the substrate; then, after the annealing treatment is completed, the substrate is taken out and cooled to room temperature; through stress relief annealing, the residual stress in the amorphous carbon film sensing layer can be effectively reduced, the stability and reliability of the film layer can be improved, and reducing stress helps to improve the long-term performance and service life of the sensor;

[0086] Step S420: Performing a square resistance test and a piezoresistance test on the substrate after stress relief annealing; the square resistance test is specifically to use a four-probe resistance tester to measure the square resistance of the amorphous carbon film sensing layer, and the square resistance range is preferably 2800KΩ±5%. If it is not within the range, it is necessary to readjust the printing parameters or annealing conditions until the requirements are met; the square resistance test ensures that the electrical properties of the amorphous carbon film sensing layer meet the design requirements, which is crucial to ensure the sensitivity and response speed of the sensor. The appropriate square resistance range helps to achieve the best working state of the sensor;

[0087] The specific steps of the piezoresistive test are to install the sensor that meets the square resistance requirements on the piezoresistive tester; apply different pressures (such as gradually increasing weight) and record the output changes of the sensor; analyze the data and ensure that the linearity (R²) is greater than 0.95, the single-point range is greater than 8kg, and the overall sensitivity is greater than 5kPa⁻¹. Only then can the piezoresistive test be passed to verify whether the actual performance of the sensor meets the expected design requirements.

[0088] Step S430: preparing an amorphous carbon film piezoresistive sensor based on the screen-printed substrate and restoring it to the target curved surface; specifically, adding electrodes to the amorphous carbon film sensing layer involves connecting a metal electrode (such as an electrode prepared by magnetron sputtering) to the sensing layer to ensure good contact between the electrode and the sensing layer; then connecting the electrode to an external circuit using a wire to ensure the reliability of signal transmission; in order to protect the amorphous carbon film sensing layer from the external environment, a protective layer can be added on top thereof, and the protective layer can be a flexible insulating material, such as a polyimide (PI) film or other suitable material; then, using an appropriate packaging material (such as a flexible epoxy resin or other flexible packaging material) to package the sensor; and finally, the prepared The sensor can be restored from a planar state to the target curved surface shape through mechanical deformation, such as bending, folding, etc., by utilizing the characteristics of the flexible substrate to enable it to adapt to the target curved surface; by restoring the sensor to the target curved surface, conformal fitting of the sensor and the target curved surface is achieved. This fitting method enables the sensor to closely follow the changes in the curved surface, thereby more accurately measuring the pressure distribution on the curved surface. Conformal fitting reduces the gap between the sensor and the target curved surface, avoids measurement errors caused by the gap, and improves the measurement accuracy of the sensor. Especially in the field of wearable devices, such as smart insoles, health monitoring equipment, etc., conformal fitting sensors can provide a more comfortable wearing experience and more accurately capture the user's physiological information.

[0089] It is difficult for the existing preparation process to ensure that after the film layer is made on the unfolded plane, it can still have good film layer quality and signal sensing ability when it is pasted back on the curved surface. In addition, the traditional preparation of the sensing layer requires the use of processes such as microelectronic printing, ultrasonic spraying, and RF sputtering. These processes are expensive and inefficient. The preparation process of the micro-nano conformal sensing amorphous carbon film piezoresistive sensor provided by the present invention adopts low-cost micro-nano conformal sensing amorphous carbon film silk screen printing combined with a micro-nano preparation composite process, that is, the micro-nano preparation technology is used in the structural layer of the sensor, and the screen printing process is used in the sensing film layer. To this end, this patent adopts the bottom layer screen printing process in the preparation of the amorphous carbon film sensing layer. The screen printing cost is low and the efficiency is high. In order to improve the quality of the screen printing film layer, the present invention adopts a special processing process: the slurry material is selected from graphene nanosheets, multi-walled carbon nanotubes and conductive ink. Subsequently, the printing slurry is dispersed and pre-processed to ensure the uniformity of the film material and the stability of the performance; in order to increase the bonding force between the substrate and the sensing film layer, the present invention pre-treats the substrate material before printing. First, the screen printing substrate is cleaned by a traditional cleaning method, and then the substrate surface is modified by oxygen plasma. The functional groups generated by the bombardment of the surface by oxygen plasma at the microscopic level are helpful for the bonding with the sensing film layer, thereby improving the adhesion between the film layer and the substrate; finally. After the sensing film layer is prepared, residual stress will be generated at the device interface. This patent adopts a cyclic annealing process to further improve the quality of the film layer; the sensing layer of the amorphous carbon film piezoresistive sensor prepared by the present invention is more stable, which improves the sensor signal quality and service life. The composite process can ensure the sensor signal quality while taking into account the economic efficiency of manufacturing.

[0090] See also Figures 4 to 6 The second technical solution of the present invention provides a micro-nano conformal sensing amorphous carbon film piezoresistive sensor, which adopts the micro-nano conformal sensing amorphous carbon film piezoresistive sensor preparation process described in the first technical solution of the present invention. The amorphous carbon film piezoresistive sensor includes a substrate layer 100 and an amorphous carbon film sensing layer 200, a microstructure layer 300 and a lead layer 400 arranged on the substrate layer 100; the amorphous carbon film sensing layer 200 is configured to be printed on the substrate using a screen printing process, and is used to sense pressure changes and convert them into electrical signals for output; the microstructure layer 300 is configured to be arranged between the amorphous carbon film sensing layer 200 and the substrate using a micro-nano preparation process, and is used to form a graphic microstructure of the amorphous carbon film piezoresistive sensor; the lead layer 400 is arranged on the top of the substrate, and is used to electrically connect the amorphous carbon film sensing layer 200 with an external circuit.

[0091] It should be noted that the sequence of the above embodiments of the present invention is only for description and does not represent the advantages and disadvantages of the embodiments. The processes depicted in the accompanying drawings do not necessarily require the specific order or continuous order shown to achieve the desired results. In some embodiments, multitasking and parallel processing are also possible or may be advantageous.

[0092] The various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

Claims

1. Preparation process of micro-nano conformal sensing amorphous carbon film piezoresistive sensor, characterized in that: The preparation process comprises: Obtaining a three-dimensional model of a target surface, and mapping the three-dimensional model to a flat screen printing mold, including: mapping the three-dimensional model to a flat flexible substrate based on a surface unfolding algorithm, including: Obtaining 3D point cloud data of the target surface and constructing a 3D surface model; Perform edge detection on the three-dimensional surface model and extract the edge with the maximum curvature gradient; The three-dimensional surface model is mapped to a plane using conformal mapping to obtain a plane unfolding diagram and the plane unfolding diagram is processed to minimize distortion and wrinkles; Prepare the sensory slurry and pre-treat the sensory slurry, including: The sensing slurry is made of graphene nanosheets, multi-walled carbon nanotubes and conductive ink to form a composite sensing slurry with a ratio of 1:1:8; Ultrasonic atomization treatment is performed on the composite sensing slurry; The composite sensing slurry after ultrasonic atomization treatment is magnetically stirred; Prepare the substrate and optimize it through micro-nano preparation processes, including: Prepare a substrate by spin coating and curing process and cut the substrate; The substrate surface is treated by oxygen plasma; The pre-treated sensing slurry is printed onto the optimized substrate using a flat screen printing mold to form an amorphous carbon film sensing layer.

2. The process for preparing a micro-nano conformal sensing amorphous carbon film piezoresistive sensor according to claim 1, characterized in that: Also includes: The substrate treated with oxygen plasma is subjected to photolithography patterning.

3. The process for preparing a micro-nano conformal sensing amorphous carbon film piezoresistive sensor according to claim 2, characterized in that: Also includes: Electrodes are prepared on a substrate that has been photolithographically patterned using magnetron sputtering.

4. The process for preparing a micro-nano conformal sensing amorphous carbon film piezoresistive sensor according to claim 3, characterized in that: The process of printing the pre-treated sensing slurry onto the optimized substrate using a silk screen mold to form an amorphous carbon film sensing layer includes: performing stress relief annealing on the substrate; Performing square resistance test and piezoresistance test on the substrate after stress relief annealing; Restore the amorphous carbon film piezoresistive sensor to the target surface.

5. A micro-nano conformal sensing amorphous carbon film piezoresistive sensor, characterized in that: The micro-nano conformal sensing amorphous carbon film piezoresistive sensor preparation process described in any one of claims 1 to 4 is adopted, and the amorphous carbon film piezoresistive sensor includes a base layer and an amorphous carbon film sensing layer, a microstructure layer and a lead layer arranged on the base layer; the amorphous carbon film sensing layer is configured to be printed on the base using a screen printing process, and is used to sense pressure changes and convert them into electrical signal output; the microstructure layer is configured to be arranged between the amorphous carbon film sensing layer and the base using a micro-nano preparation process, and is used to form a graphic microstructure of the amorphous carbon film piezoresistive sensor; the lead layer is arranged on the top of the base, and is used for electrically connecting the amorphous carbon film sensing layer with an external circuit.

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