A preparation process of a flexible temperature-stress sensor and a flexible sensor

Abstract

The present invention discloses a preparation process of a flexible temperature-stress sensor, comprising the following steps: preparing a flexible substrate by spin coating using a PDMS solution; preparing a MXene-CNTs stress composite film; preparing a PEDOT:PSS-CNTs-graphene thermosensitive composite film; preparing a SiC film as a dielectric layer; preparing an electrode layer of an equivalent neural conductive network structure; vertically laminating a flexible substrate, an electrode layer, a stress composite film, a dielectric layer, a thermosensitive composite film, an electrode layer, and a flexible substrate in a bottom-to-top order, wherein the lead of the upper electrode layer is placed in the X-axis direction, and the lead direction of the lower electrode layer is placed in the Y-axis direction for vertical lamination, to prepare a flexible temperature-stress sensor. The flexible sensor prepared by the present invention takes into account multiple detection capabilities of temperature and stress, wherein temperature sensing is reacted by the magnitude of the thermoelectric potential, and stress sensing is reacted by the magnitude of the resistance, and the sensing mechanisms are different, which is convenient for temperature and stress decoupling, avoids signal crosstalk, and improves the accuracy of measurement.

Description

Technical Field

[0001] The invention belongs to the technical field of sensors, and in particular relates to a preparation process of a temperature-stress flexible sensor and a flexible sensor. Background Art

[0002] With the development of electronic technology, people's demand for high-performance flexible sensors is also increasing. Most existing flexible sensors for measuring temperature or stress can generally only recognize one of the signals separately, but this single-mode sensor cannot provide enough information for the sensing system. Therefore, it is necessary to develop multifunctional flexible sensors with different modes to monitor and distinguish various external stimuli.

[0003] Most of the existing multifunctional flexible sensors use multiple individual sensors partitioned or stacked arrays on the same flexible sensor. Each sensor is composed of a sensitive layer placed in the middle, electrode layers on both sides, and flexible substrates above and below. This makes integration difficult, the device structure complex, and is not conducive to miniaturization. In addition, the sensitive layer has a single sensing material, unstable performance, a small measurement range, and low sensitivity. Another method is to achieve multi-stimulus sensing by coating a single structure with multifunctional materials to reduce the complexity of the structure, but due to the single sensing mechanism, signal crosstalk will occur, affecting the sensitivity of the sensor. Summary of the invention

[0004] The purpose of the present invention is to overcome the problems of the prior art such as single sensing function, easy coupling of sensing signals, complex structure and insensitivity to external stimuli, and to provide a preparation process of a flexible temperature-stress sensor and a flexible sensor with simple structure, sensitivity to external stimuli and no crosstalk between signals.

[0005] The technical solution adopted by the present invention is a preparation process of a flexible temperature-stress sensor, comprising the following steps:

[0006] Step 1: Prepare a flexible substrate by spin coating using a PDMS solution;

[0007] Step 2: Mix the carbon nanotube solution and the MXene nanosheet solution in a volume ratio of 1:1, filter the mixed solution after ultrasonic treatment, and dry the filtrate in a vacuum oven to prepare a MXene-CNTs stress composite film;

[0008] Step 3: Mix the conductivity enhancer and the PEDOT:PSS aqueous solution in a volume ratio of 3 to 4:1 to obtain a mixed solution, then add the carbon nanotube-graphene carbon material mixture to the mixed solution in a mass ratio of 1:1, and finally add 10 times the weight of the carbon material mixture sodium dodecylbenzene sulfonate powder; fully stir the mixed solution, perform ultrasonic treatment, filter the solution, and place the filtrate in a vacuum oven to dry, so as to prepare a PEDOT:PSS-CNTs-graphene thermosensitive composite film;

[0009] Step 4: preparing a SiC film as a dielectric layer by chemical vapor deposition;

[0010] Step 5: Using screen printing technology to prepare an electrode layer of an equivalent neural conductive network structure;

[0011] Step 6: Plasma treatment is performed on the stress composite film layer, dielectric layer, thermosensitive composite film layer, and electrode layer obtained in the above steps, and the flexible substrate, electrode layer, stress composite film, dielectric layer, thermosensitive composite film, electrode layer, and flexible substrate are vertically bonded in order from bottom to top. During bonding, the leads of the upper electrode layer are arranged in the direction of the X-axis, and the leads of the lower electrode layer are arranged in the direction of the Y-axis for vertical bonding to prepare a flexible temperature-stress sensor.

[0012] Furthermore, the preparation method of the electrode layer is specifically as follows:

[0013] E1. Prepare the screen printing plate: draw the pattern on the screen printing brush, embed the frame around the screen printing mesh and apply photosensitive glue, expose it to sunlight and dry it; wipe off the photosensitive glue on the surface of the pattern to obtain the screen printing plate. The obtained screen printing plate presents a 9×9 rectangular array, and the diameter of each circle is 100~200um and the thickness is 10~20um;

[0014] E2. Prepare conductive paste: Add conductive silver paste into a glass cup, add appropriate amount of boiling water, and use a glass rod to fully mix the two materials until the conductive silver paste on the glass rod can be drawn and flowed down;

[0015] E3. Install the screen printing plate and substrate: Use anhydrous alcohol to rinse the surface of the substrate, then dry it, install it flat on the printing table, and lay the screen printing plate flat on the substrate;

[0016] E4. Printing electrode layer: Fill the conductive silver paste onto one side of the screen printing plate, use a scraper to repeatedly scrape the template 2 to 3 times, so that the conductive silver paste can pass through the mesh and print onto the underlying substrate, then dry the substrate to fully solidify the conductive silver paste, and remove it to obtain the electrode layer.

[0017] Furthermore, the preparation method of the dielectric layer is specifically as follows: single crystal silicon is used as a substrate, tetramethylsilane is used as a reaction gas source, hydrogen is used as a carrier gas, the background vacuum degree is less than 3.0×10-4Pa, and before coating, H2 introduced into the vacuum chamber is activated into plasma by a radio frequency power supply and maintained for 20 minutes. During the thin film deposition process, the flow rate of the working gas is adjusted by a mass flow controller, and the gas molecules are ionized by a radio frequency power supply to deposit a SiC thin film. After coating, the SiC thin film is treated with H2 for 30 minutes to obtain the dielectric layer.

[0018] Furthermore, in step one, a clean silicon wafer cleaned with acetone, anhydrous ethanol and DI is used as a substrate, and a curing agent-flexible silicone mixture with a mass ratio of 10:1 is first spin-coated at a rotation speed of 2000 rpm for 30 seconds, and then the PDMS solution is spin-coated at a rotation speed of 1500 rpm for 10 seconds. The silicon substrate with PDMS is then placed on a constant temperature heating table and cured at 80°C for 120-150 minutes. After the PDMS is cured, it is removed and cut to obtain a flexible substrate.

[0019] Furthermore, the preparation method of the carbon nanotube solution in step 2 is: taking carbon nanotube powder and adding it to a mixed solution of concentrated HNO3 and concentrated H2SO4 in a volume ratio of 1:3, ultrasonicating for 5 hours, cooling, precipitating to remove residual acid, and then washing with distilled water for multiple times, filtering until the solution is neutral when compared with pH paper, and drying at a temperature of 110°C to obtain acidified carbon nanotubes; dissolving the acidified carbon nanotubes in deionized water of sodium dodecylbenzene sulfonate, and ultrasonicating for 30 minutes to form a carbon nanotube solution.

[0020] Furthermore, the preparation method of the MXene nanosheet solution is: mixing and stirring MAX powder with an etchant, then centrifuging and filtering the mixture to separate the solid, and then washing with deionized water until the pH value reaches 4 to 6, at which time a multilayer MXene with an accordion-like structure is obtained, and further centrifuging and ultrasonic treatment are performed to obtain a single-layer or few-layer two-dimensional MXene nanosheet solution.

[0021] Furthermore, in the step 2 of preparing the stress composite film, the mixed solution is ultrasonically treated for 40 minutes, filtered through a filter membrane with a pore size of 200 nm, and the vacuum oven temperature is 80°C.

[0022] Furthermore, in the step 3, when preparing the thermosensitive composite film, a 1.3 wt % PEDOT:PSS aqueous solution is used, and the ratio of PEDOT to PSS is 5:8.

[0023] Furthermore, in the step 3 of preparing the thermosensitive composite film, the mixed solution is treated in an ice-water bath for 45 minutes using an ultrasonic disperser; filtered using a filter membrane with a pore size of 200 nm, and the vacuum oven temperature is 80°C.

[0024] A flexible temperature-stress sensor is manufactured by adopting a manufacturing process of a flexible temperature-stress sensor, wherein slots in a dumbbell structure are radially provided on the dielectric layer.

[0025] The present invention adopts a vertical stacking structure to prepare a multifunctional temperature-stress integrated flexible sensor. The sensor includes an upper sensor and a lower sensor laminated together and a dielectric layer located between the two sensors. The upper sensor is composed of a thermosensitive composite film composed of poly (3, 4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT: PSS) polymer, carbon nanotubes (CNTs) and graphene materials, an upper electrode layer of an equivalent neural network structure, and a top flexible substrate from bottom to top. The lower sensor is composed of a bottom flexible substrate, a lower electrode layer of an equivalent neural network structure, and a stress composite film composed of MXene and CNTs materials from bottom to top. The PEDOT: PSS-CNTs-graphene thermosensitive composite film of the upper sensor responds to temperature signals, and the MXene-CNTs stress composite film of the lower sensor responds to stress changes, and conducts electricity in combination with the upper and lower equivalent neural network electrode layers to achieve simultaneous sensing and output of temperature-stress dual functions.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] 1) The flexible sensor prepared by the present invention has multiple detection capabilities of temperature and stress. The temperature sensing is reacted by the magnitude of the thermoelectric potential, and the stress sensing is reacted by the magnitude of the resistance. The different sensing mechanisms facilitate the decoupling of temperature and stress, avoid signal crosstalk, and improve the accuracy of measurement;

[0028] 2) Use an equivalent neural network structure to implement the design of the electrode layer, enhance the conduction rate between signals, improve the sensitivity of the flexible sensor, simplify the assembly steps of the sensor, and reduce production costs;

[0029] 3) The upper electrode layer and the lower electrode layer form an equivalent neural conductive network structure to realize signal transmission inside the entire sensor; a dielectric layer is sandwiched between the two sensor units to redistribute electrons and optimize signal transmission;

[0030] 4) Combine multiple materials with excellent properties to enhance the mechanical strength of flexible sensors and improve the sensing performance of flexible sensors;

[0031] 5) The structure is designed with vertical stacking to achieve the purpose of lightweight and miniaturization;

[0032] 6) Both sides of the SiC film are etched into an inverted ladder structure, and finally an inverted ladder dumbbell dielectric layer structure is formed. This structure has the advantages of high thermal conductivity and high electron mobility, which is beneficial to the transmission of signals between the upper and lower reaction layers and improves the sensitivity of the flexible sensor.

[0033] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The figure is a process flow chart of the preparation of the flexible temperature-stress sensor of the present invention;

[0035] Figure 2 It is a schematic diagram of the overall structure of the flexible sensor of the present invention;

[0036] Figure 3 It is a schematic diagram of the conduction mechanism of MXene-CNTs stress composite film;

[0037] Figure 4 is the SEM image of PEDOT:PSS-CNTs-graphene thermosensitive composite film;

[0038] Figure 5 It is a schematic diagram of the conduction mechanism of PEDOT:PSS-CNTs-graphene thermosensitive composite film;

[0039] Figure 6 It is a process flow chart of screen printing the electrode layer of the equivalent neural conductive network structure;

[0040] Figure 7 It is a schematic diagram of the structural principle of the equivalent neural conductive network;

[0041] Figure 8 A deep etching process flow chart for preparing a dielectric layer;

[0042] Fig. 9 Schematic diagram of the dielectric layer of the inverted ladder-shaped dumbbell structure. DETAILED DESCRIPTION

[0043] The present invention is further explained below in conjunction with the accompanying drawings and embodiments to facilitate better understanding by those skilled in the art.

[0044] Example 1

[0045] like Figure 1-9 As shown, a preparation process of a flexible temperature-stress sensor includes the following steps:

[0046] Step 1, prepare a flexible substrate: use a clean silicon wafer cleaned with acetone, anhydrous ethanol and DI as the substrate, spray a layer of release agent evenly on the silicon wafer to facilitate the subsequent smooth demolding and molding, stir at 2000rpm for 30 seconds to spin-coat a curing agent-flexible silicone mixture with a mass ratio of 10:1, and then spin-coat the PDMS solution at a speed of 1500rpm for 10 seconds, and then place the silicon substrate with PDMS on a constant temperature heating table and cure at 80°C for 120-150 minutes. After the PDMS is cured, remove it and cut it to obtain the flexible substrate. Substrates of different thicknesses can be obtained by controlling the number of spin coatings. The thickness of the flexible substrate prepared in this application is 100μm-300μm.

[0047] Step 2: Prepare a stress composite film: mix the carbon nanotube solution and the MXene nanosheet solution in a volume ratio of 1:1, filter the mixed solution after ultrasonic treatment, and dry the filtrate in a vacuum oven to prepare a MXene-CNTs stress composite film.

[0048] Among them, the preparation method of the carbon nanotube solution is: take 20 mg of carbon nanotube powder and add it to 10 ml of a mixed solution of concentrated HNO3 and concentrated H2SO4 with a volume ratio of 1:3, ultrasonicate for 5 hours, cool, precipitate to remove residual acid, then wash with distilled water for many times, filter until the pH value of the solution is neutral using a pH test paper, and dry at a temperature of 110°C to obtain acidified carbon nanotubes; dissolve 0.1 g of the acidified carbon nanotubes in 50 ml of deionized water containing 0.05 g of sodium dodecylbenzene sulfonate (SDBS), and ultrasonicate for 30 minutes to form a carbon nanotube solution.

[0049] The purpose of acid-treating carbon nanotubes is to prevent agglomeration or large-area aggregation during the preparation process, which would affect the performance of the composite material. The carbon nanotubes are single-walled carbon nanotubes (SWNTs).

[0050] The preparation method of the MXene nanosheet solution is: MAX powder is mixed and stirred with an etchant, and then the mixture is centrifuged and filtered to separate the solid, and then washed with deionized water until the pH value reaches 4 to 6, at which time a multilayer MXene with an accordion-like structure is obtained, and further centrifuged and ultrasonically treated to obtain a single-layer or few-layer two-dimensional MXene nanosheet solution.

[0051] In this embodiment, a MXene (Ti3C2Tx) nanosheet solution is mainly prepared. First, 1g LiF is dissolved in 5ml hydrochloric acid solution, 1g TisAlC2 powder is added and stirred for 10 minutes, and then the suspension is moved to a 40°C water bath, stirred and maintained for 10 hours. After the reaction is completed, the suspension is poured into a centrifuge tube and centrifuged at a speed of 3500rpm for 5 minutes. After the centrifugation is completed, the supernatant is poured out and deionized water is added to shake well, and the supernatant is repeatedly centrifuged until the pH of the supernatant is greater than 4, thereby obtaining the MXene (Ti3C2Tx) nanosheet solution.

[0052] Step 3, preparation of thermosensitive composite film: in 20mL ultrapure water, add 0.3ml of dimethyl sulfoxide (DMSO) as a conductivity enhancer, and then add it to 6ml PEDOT:PSS aqueous solution, the PEDOT:PSS aqueous solution uses a 1.3wt% PEDOT:PSS aqueous solution, and the ratio of PEDOT to PSS is 5:8. Then add the carbon nanotube-graphene carbon material mixture to the mixed solution at a mass ratio of 1:1, and finally add 10 times the weight of the carbon material mixture. Sodium dodecylbenzene sulfonate powder; stir the mixed solution thoroughly, and then treat it in an ice water bath for 45min in an ultrasonic disperser to obtain a PEDOT:PSS-CNTs-graphene thermosensitive composite material solution. The above solution is filtered through a filter membrane with a pore size of 200nm, and the filtrate is placed in a vacuum oven at 80℃ to dry, and finally the PEDOT:PSS-CNTs-graphene thermosensitive composite film is obtained.

[0053] Step 4: Prepare a dielectric layer: The present invention adopts chemical vapor deposition to prepare a SiC thin film as a dielectric layer. The manufacturing process of the dielectric layer specifically includes:

[0054] C1. Formation of SiC film: In the experimental device, single crystal silicon is used as the substrate, tetramethylsilane is used as the reaction gas source, and hydrogen is used as the carrier gas. Before coating, the H2 introduced into the vacuum chamber is activated into plasma by a radio frequency power supply and maintained for 20 minutes, so that the background vacuum is less than 3.0×10 -4 Pa, during the film deposition process, the flow rate of the working gas is regulated by a mass flow controller, and the gas molecules are ionized by a radio frequency power supply to deposit the SiC film. After coating, H2 treatment is carried out for 30 minutes to obtain the SiC film.

[0055] C2. Spin coating negative photoresist: Use negative photoresist HSQ as a mask, and use a spin machine to spin at a speed of 3000r / s for 40s to evenly cover the surface of the SiC film. After spin coating, soft baking is performed to remove the solvent in the photoresist;

[0056] C3, Alignment and exposure: Position the SiC film within the focus range of the optical system, align the alignment marks with the matching marks on the mask, perform exposure, transfer the image to the photoresist, and then bake to promote the chemical reaction of the photoresist;

[0057] C4, Development: Use chemical developer to treat for 100s to dissolve the unexposed part, and leave the exposed part after rinsing, so that the pattern can be accurately copied into the photoresist. After development, vertical film baking is performed to evaporate the remaining solvent in the photoresist and make the photoresist hard;

[0058] C5. Etching: Etching is performed using the ICP deep etching process. The ICP system has two independent RF power supplies: source power RF1 and RF power RF2. RF1 can obtain high-density active ions through the inductive coupling mode to control the etching rate. RF power RF2 controls the bombardment energy by adding a bias voltage to the electrode outside the cavity, so that the plasma acts vertically on the substrate, and the reaction generates volatile gaseous substances to achieve the purpose of etching. Therefore, by controlling two independent RF power supplies, an inverted V-shaped groove can be etched on the SiC film. Set the chamber pressure to 7 mTorr, the source power to 500 W, the RF power to 20W, add the passivation gas C4F8 at a flow rate of 20 mL / min, and etch for 30 minutes, and finally form an inverted trapezoidal groove on the SiC film.

[0059] C6. Mask removal: Use HF plus deionized water or ammonia water to remove the HSQ photoresist to obtain a SiC film with an inverted ladder structure.

[0060] The SiC film is peeled off from the Si substrate through a peeling process, and the back of the SiC film is etched again through steps C1 to C6, so that both sides of the SiC film are etched into an inverted ladder structure, and finally an inverted ladder dumbbell structure dielectric layer structure is formed.

[0061] Step 5: Prepare an electrode layer: Use screen printing technology to prepare an electrode layer of an equivalent neural conductive network structure; the preparation method of the electrode layer is specifically as follows:

[0062] E1. Prepare the screen printing plate: draw the pattern on the screen printing brush, embed the frame around the screen printing mesh and apply photosensitive glue, expose it to sunlight and dry it; wipe off the photosensitive glue on the surface of the pattern to obtain the screen printing plate. The obtained screen printing plate presents a 9×9 rectangular array, and the diameter of each circle is 100~200um and the thickness is 10~20um;

[0063] E2. Prepare conductive paste: Add conductive silver paste into a glass cup, add appropriate amount of boiling water, and use a glass rod to fully mix the two materials until the conductive silver paste on the glass rod can be drawn and flowed down;

[0064] E3. Install the screen printing plate and substrate: Use anhydrous alcohol to rinse the surface of the substrate, then dry it, install it flat on the printing table, and lay the screen printing plate flat on the substrate;

[0065] E4. Printing electrode layer: Fill the conductive silver paste onto one side of the screen printing plate, use a scraper to repeatedly scrape the template 2 to 3 times, so that the conductive silver paste can pass through the mesh and print onto the underlying substrate, then dry the substrate to fully solidify the conductive silver paste, and remove it to obtain the electrode layer.

[0066] Step 6, packaging: The stress composite film layer, dielectric layer, thermosensitive composite film layer, and electrode layer prepared in the above steps are subjected to plasma treatment, and the flexible substrate, electrode layer, stress composite film, dielectric layer, thermosensitive composite film, electrode layer, and flexible substrate are vertically laminated in order from bottom to top. During the lamination, the leads of the upper electrode layer are arranged in the direction of the X-axis, and the leads of the lower electrode layer are arranged in the direction of the Y-axis for vertical lamination to obtain a flexible temperature-stress sensor.

[0067] Example 2

[0068] A flexible temperature-stress sensor is made by a preparation process of a flexible temperature-stress sensor, including an upper sensor and a lower sensor laminated together and a dielectric layer located between the two sensors. The upper sensor is composed of a thermosensitive composite film composed of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) polymer, carbon nanotubes (CNTs) and graphene materials, an upper electrode layer of an equivalent neural network structure, and a top flexible substrate from bottom to top. The lower sensor is composed of a bottom flexible substrate, a lower electrode layer of an equivalent neural network structure, and a stress composite film composed of MXene and CNTs materials from bottom to top. The PEDOT:PSS-CNTs-graphene thermosensitive composite film of the upper sensor responds to temperature signals, and the MXene-CNTs stress composite film of the lower sensor responds to stress changes, and conducts electricity in combination with the upper and lower equivalent neural network electrode layers to achieve simultaneous sensing and output of temperature-stress dual functions. A dielectric layer is sandwiched between the two sensing units to redistribute electrons and optimize signal transmission.

[0069] The PEDOT:PSS used in the present invention is a conductive polymer with good thermoelectric effect. Adding carbon nanotubes to PEDOT:PSS can improve the conductivity and thermal performance of the composite material because the structure of carbon nanotubes makes the surface area, diameter and length ratio relatively large, and it is easier to form a conductive path when in contact with them. Figure 5As shown in A0, carbon nanotubes and PEDOT molecules form π-π bonds, which tightly bind the two materials. At the same time, PEDOT:PSS can stabilize and disperse carbon nanotubes in the solution, making the two materials complementary. Adding graphene to fill the gaps in the composite material further enhances the thermoelectric effect of the composite material. Figure 4 (a) (b) are SEM images of the thermosensitive composite film, from which it can be seen that PEDOT:PSS, carbon nanotubes, and graphene are fully mixed and dispersed. Figure 5 It is the conduction principle of the thermosensitive composite film. When there is a temperature difference between the upper electrode layer and the lower electrode layer, an electromotive force will be generated on the upper and lower electrode surfaces of the material due to the Seebeck effect of the composite material. The temperature difference can be judged according to the size of the thermoelectric electromotive force, thereby determining the temperature, thereby realizing the temperature sensing function.

[0070] Sensing mechanism of stress composite film: The MXene used in the present invention is a two-dimensional layered material similar to graphene, which has the advantages of good conductivity and rich surface functional groups. Adding one-dimensional materials such as carbon nanotubes can serve as a bridge to connect the layered MXene, reduce the interaction between MXene sheets and construct a new conductive network, so that the sensor has higher sensitivity and a wider strain sensing range. Figure 3 As shown in A1, when there is no external stress on the flexible substrate and the stress composite film, the internal connection paths of the stress composite film increase, which reduces its resistance. Figure 3 As shown in A2, when external stress is added, cracks first occur in the area where the stress is concentrated, and gradually expand as the stress increases. As the cracks increase, the connection path inside the stress composite film decreases, and the resistance gradually increases. Figure 3 As shown in A3, when the external stress increases further, the overlapping area between the MXene layers in the stress composite film decreases due to slippage, the connection path decreases, and the resistance continues to increase. Therefore, the magnitude of the external stress can be reflected by measuring the size of its resistance value.

[0071] The structural principle of the electrode layer of the equivalent neural conductive network: Figure 7 As shown, the equivalent neural conductive network structure of the present invention is mainly composed of an upper electrode layer, a lower electrode layer and a conductive composite film located between the upper and lower electrode layers. When power is turned on, the protruding nanosheets in the conductive composite film contact the upper electrode to form a plurality of stimulation electrodes, which are connected to the lower electrode through a one-dimensional conductive material network mixed in the conductive composite film to form a complete conductive path. The equivalent neural network of its microstructure can be divided into three network layers, namely, the input layer B1, the hidden layer B2 and the output layer B3. Each network layer contains a plurality of neurons, and each neuron is connected to the adjacent neuron of the previous layer to realize the closed conduction of circuit input and output.

[0072] like Figure 8-9 As shown in the figure, both sides of the SiC film are etched into an inverted ladder structure, and finally a dielectric layer structure E1 with an inverted ladder dumbbell structure is formed. E2 is an enlarged view of the dielectric layer structure, and DD is a cross-sectional view of the enlarged view. This structure has the advantages of high thermal conductivity and high electron mobility, which is conducive to the transmission of signals between the upper and lower reaction layers and improves the sensitivity of the flexible sensor.

[0073] The present invention realizes the sensing of temperature and stress simultaneously through the input and output of the equivalent neural conductive network structure, by using the characteristic that the magnitude of the thermoelectric potential of the thermosensitive composite film changes consistently with temperature, and the characteristic that the resistance of the stress composite film changes consistently with stress. The problem of the prior art of single sensing function, easy coupling of sensing signals, complex structure, and insensitivity to external stimuli is overcome, and a flexible temperature-stress multifunctional sensor is provided, which has a simple structure, is sensitive to external stimuli, and is not prone to crosstalk between signals.

[0074] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or substitutions within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A process for preparing a flexible temperature-stress sensor, characterized in that: The following steps are involved: Step 1: Prepare a flexible substrate by spin coating using a PDMS solution; Step 2: Mix the carbon nanotube solution and the MXene nanosheet solution in a volume ratio of 1:1, filter the mixed solution after ultrasonic treatment, and dry the filtrate in a vacuum oven to prepare a MXene-CNTs stress composite film; Step 3: Mix the conductivity enhancer and the PEDOT:PSS aqueous solution in a volume ratio of 3 to 4:1 to obtain a mixed solution, then add the carbon nanotube-graphene carbon material mixture to the mixed solution in a mass ratio of 1:1, and finally add 10 times the weight of the carbon material mixture sodium dodecylbenzene sulfonate powder; fully stir the mixed solution, perform ultrasonic treatment, filter the solution, and place the filtrate in a vacuum oven to dry, so as to prepare a PEDOT:PSS-CNTs-graphene thermosensitive composite film; Step 4: preparing a SiC film as a dielectric layer by chemical vapor deposition; The method for preparing the dielectric layer is specifically as follows: using single crystal silicon as a substrate, tetramethylsilane as a reaction gas source, hydrogen as a carrier gas, the background vacuum degree is less than 3.0×10-4Pa, before coating, using a radio frequency power supply to activate H2 introduced into a vacuum chamber into plasma and maintain it for 20 minutes, during the film deposition process, the flow rate of the working gas is adjusted by a mass flow controller, and the radio frequency power supply is used to ionize the gas molecules, thereby depositing a SiC film, and after coating, the SiC film is treated with H2 for 30 minutes to obtain the dielectric layer; Step 5, preparing an electrode layer of an equivalent neural conductive network structure; the equivalent neural conductive network structure is composed of an upper electrode layer, a lower electrode layer and a conductive composite film located between the upper and lower electrode layers; when power is turned on, the protruding nanosheets in the conductive composite film contact the upper electrode to form a plurality of stimulation electrodes, which are connected to the lower electrode through a one-dimensional conductive material network doped in the conductive composite film to form a complete conductive path; The equivalent neural network of its microstructure can be divided into three network layers, namely input layer B1, hidden layer B2 and output layer B3. Each network layer contains multiple neurons, and each neuron is connected to the adjacent neurons of the previous layer to achieve closed conduction of circuit input and output. Step 6: Plasma treatment is performed on the stress composite film layer, dielectric layer, thermosensitive composite film layer, and electrode layer obtained in the above steps, and the flexible substrate, electrode layer, stress composite film, dielectric layer, thermosensitive composite film, electrode layer, and flexible substrate are vertically bonded in order from bottom to top. During bonding, the leads of the upper electrode layer are arranged in the direction of the X-axis, and the leads of the lower electrode layer are arranged in the direction of the Y-axis for vertical bonding to prepare a flexible temperature-stress sensor.

2. The preparation process of a flexible temperature-stress sensor according to claim 1, characterized in that: The preparation method of the electrode layer is specifically as follows: E1. Prepare the screen printing plate: draw the pattern on the screen printing brush, embed the frame around the screen printing mesh and apply photosensitive glue, expose it to sunlight and dry it; wipe off the photosensitive glue on the surface of the pattern to obtain the screen printing plate. The obtained screen printing plate presents a 9×9 rectangular array, and the diameter of each circle is 100~200um and the thickness is 10~20um; E2. Prepare conductive paste: Add conductive silver paste into a glass cup, add appropriate amount of boiling water, and use a glass rod to fully mix the two materials until the conductive silver paste on the glass rod can be drawn and flowed down; E3. Install the screen printing plate and substrate: Use anhydrous alcohol to rinse the surface of the substrate, then dry it, install it flat on the printing table, and lay the screen printing plate flat on the substrate; E4. Printing electrode layer: Fill the conductive silver paste onto one side of the screen printing plate, use a scraper to repeatedly scrape the template 2 to 3 times, so that the conductive silver paste can pass through the mesh and print onto the underlying substrate, then dry the substrate to fully solidify the conductive silver paste, and remove it to obtain the electrode layer.

3. The preparation process of a flexible temperature-stress sensor according to claim 1, characterized in that: In step 1, a clean silicon wafer cleaned with acetone, anhydrous ethanol and DI is used as the substrate. First, a curing agent-flexible silicone mixture with a mass ratio of 10:1 is spin-coated at a speed of 2000 rpm for 30 seconds, and then a PDMS solution is spin-coated at a speed of 1500 rpm for 10 seconds. The silicon substrate with PDMS is then placed on a constant temperature heating table and cured at 80°C for 120-150 minutes. After the PDMS is cured, it is removed and cut to obtain a flexible substrate.

4. The preparation process of a flexible temperature-stress sensor according to claim 1, characterized in that: The preparation method of the carbon nanotube solution in step 2 is as follows: taking carbon nanotube powder and adding it to a mixed solution of concentrated HNO3 and concentrated H2SO4 in a volume ratio of 1:3, ultrasonicating for 5 hours, cooling, precipitating to remove residual acid, then washing with distilled water for multiple times, filtering until the solution is neutral when compared with pH paper, and drying at a temperature of 110°C to obtain acidified carbon nanotubes; dissolving the acidified carbon nanotubes in deionized water of sodium dodecylbenzene sulfonate, and ultrasonicating for 30 minutes to form a carbon nanotube solution.

5. The preparation process of a flexible temperature-stress sensor according to claim 1, characterized in that: The preparation method of the MXene nanosheet solution is: MAX powder is mixed and stirred with an etchant, and then the mixture is centrifuged and filtered to separate the solid, and then washed with deionized water until the pH value reaches 4 to 6, at which time a multilayer MXene with an accordion-like structure is obtained, and further centrifuged and ultrasonically treated to obtain a single-layer or few-layer two-dimensional MXene nanosheet solution.

6. The preparation process of a flexible temperature-stress sensor according to claim 1, characterized in that: In the step 2 of preparing the stress composite film, the mixed solution is ultrasonically treated for 40 minutes, filtered through a filter membrane with a pore size of 200 nm, and the vacuum oven temperature is 80° C.

7. The process for preparing a flexible temperature-stress sensor according to claim 1, characterized in that: In the step 3, when preparing the thermosensitive composite film, a 1.3 wt % PEDOT:PSS aqueous solution is used, and the ratio of PEDOT to PSS is 5:

8.

8. The process for preparing a flexible temperature-stress sensor according to claim 1, characterized in that: In the step 3, when preparing the thermosensitive composite film, the mixed solution is treated in an ice water bath for 45 minutes using an ultrasonic disperser; filtered using a filter membrane with a pore size of 200 nm, and the vacuum oven temperature is 80° C.

9. A flexible temperature-stress sensor, characterized in that: The flexible temperature-stress sensor is manufactured by adopting the preparation process of any one of claims 1 to 8, wherein slots in a dumbbell structure are radially opened on the dielectric layer.

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