Flexible sensor and preparation method thereof

Abstract

The invention relates to a flexible sensor and a preparation method thereof, the flexible sensor comprises a temperature sensing film and a pressure sensing film which are stacked, one side, far away from the pressure sensing film, of the temperature sensing film is provided with a temperature sensing coil, and one side, close to the temperature sensing film, of the pressure sensing film is provided with a plurality of pyramid structures. The method comprises the following steps: forming a temperature sensing coil on a flexible substrate to obtain a temperature sensing film; enabling a mixture of a conductive material and a high polymer material to pass through a pyramid cone structure template to prepare a pressure sensing film with a plurality of pyramid cone structures on one side; a temperature sensing film and a pressure sensing film are assembled, the side, provided with the temperature sensing coil, of the temperature sensing film is made to be away from the pressure sensing film, the side, provided with the multiple pyramid cone structures, of the pressure sensing film is made to be close to the temperature sensing film, and the flexible sensor is obtained. The flexible sensor with pressure-temperature dual-mode sensing is formed through the temperature sensing film and the pressure sensing film.

Description

Technical Field

[0001] This application relates to the technical field of sensors, and particularly to flexible sensors and their preparation methods. Background Art

[0002] Traditional pressure sensors and temperature sensors are mostly rigid and cannot be stretched or bent arbitrarily, which limits their application in robot electronic skin. For example, as the skin of the robot joint part, they are prone to losing the sensing function and sensitivity under the state of stretching and bending. Therefore, it is required that the sensor has a certain flexibility, high sensitivity and detection range. Most of the flexible pressure-temperature sensors that can simultaneously detect pressure and temperature stimuli have complex structures and cumbersome manufacturing processes, which are not conducive to the large-scale array of devices. In addition, flexible pressure-temperature sensors generally have signal coupling problems. A large number of studies use temperature algorithms for signal processing. However, due to the changing application environment, the temperature algorithm needs to be calibrated frequently, making the measurement more complex and the application limited. Summary of the Invention

[0003] In view of the above technical problems, this application provides a flexible sensor and its preparation method, which can form a flexible sensor with pressure-temperature dual-mode sensing.

[0004] To solve the above technical problems, in the first aspect, this application provides a flexible sensor, including a temperature sensing film and a pressure sensing film stacked, a temperature sensing coil is provided on the side of the temperature sensing film away from the pressure sensing film, and a plurality of pyramid cone structures are distributed on the side of the pressure sensing film close to the temperature sensing film.

[0005] In one embodiment, interdigital electrodes are provided on the side of the temperature sensing film close to the pressure sensing film.

[0006] In one embodiment, the flexible sensor further includes a columnar substrate, and the side of the temperature sensing film provided with the temperature sensing coil is close to the columnar substrate.

[0007] In one embodiment, the plurality of pyramid cone structures include pyramid cones of different sizes.

[0008] In one embodiment, the mass fraction of the conductive material in the pressure sensing film accounts for 5% - 15% of the total mass.

[0009] In the second aspect, this application also provides a preparation method of a flexible sensor, including the following steps:

[0010] S1. Form a temperature sensing coil on a flexible substrate to obtain a temperature sensing film;

[0011] S2. Provide a pyramid cone structure template;

[0012] S3. Pass the mixture of the conductive material and the polymer material through the pyramid cone structure template to prepare a pressure sensing film with multiple pyramid cone structures on one side.

[0013] S4. Assemble the temperature sensing film and the pressure sensing film, with the side of the temperature sensing film having the temperature sensing coil away from the pressure sensing film and the side of the pressure sensing film having multiple pyramid cone structures close to the temperature sensing film to obtain a flexible sensor.

[0014] In one embodiment, the S1 step includes:

[0015] Sputter a temperature-sensitive material on the flexible substrate to form a temperature sensing coil.

[0016] Encapsulate the temperature sensing coil to form a first encapsulation layer.

[0017] Form interdigital electrodes on the first encapsulation layer to obtain a temperature sensing film.

[0018] In one embodiment, the S2 step includes:

[0019] Form a microsphere film through a microsphere self-assembly process.

[0020] Etch the microspheres in the microsphere film to make them smaller and form a mask template on the microsphere film.

[0021] Place the mask template on the substrate and perform anisotropic etching on the substrate to prepare a pyramid cone structure template.

[0022] In one embodiment, the forming of the microsphere film through the microsphere self-assembly process includes:

[0023] Provide a silicon wafer and perform a hydrophilic treatment on the silicon wafer.

[0024] Place the silicon wafer obliquely and extrude the microsphere suspension from the higher side of the silicon wafer along the silicon wafer so that the microsphere suspension diffuses on the surface of the silicon wafer to form microspheres.

[0025] Place the silicon wafer in plasma water so that the microspheres on the silicon wafer float and disperse on the water surface.

[0026] Add a sodium dodecyl sulfate solution to the plasma water so that the microspheres on the water surface aggregate into a film to obtain a microsphere film.

[0027] In one embodiment, the S3 step includes:

[0028] Add the conductive material to the polymer material precursor and mix evenly to obtain a mixture.

[0029] Spin coat the mixture on the pyramid cone structure template;

[0030] Carry out curing and demolding treatment on the mixture to obtain a pressure sensing film with multiple pyramid cone structures on one side.

[0031] The flexible sensor and its preparation method of the present application. The flexible sensor includes a temperature sensing film and a pressure sensing film which are stacked. A temperature sensing coil is provided on the side of the temperature sensing film away from the pressure sensing film, and multiple pyramid cone structures are distributed on the side of the pressure sensing film close to the temperature sensing film. The preparation method of the flexible sensor includes: forming a temperature sensing coil on a flexible substrate to obtain a temperature sensing film; providing a pyramid cone structure template; passing a mixture of a conductive material and a polymer material through the pyramid cone structure template to prepare a pressure sensing film with multiple pyramid cone structures on one side; assembling the temperature sensing film and the pressure sensing film, making the side of the temperature sensing film with the temperature sensing coil away from the pressure sensing film, and making the side of the pressure sensing film with multiple pyramid cone structures close to the temperature sensing film to obtain a flexible sensor. A flexible sensor with pressure-temperature dual-mode sensing is formed through the temperature sensing film and the pressure sensing film. Description of the Drawings

[0032] Figure 1 is a side view and a cross-sectional view of the flexible sensor shown according to an embodiment of the present application;

[0033] Figure 2 is a side view and a cross-sectional view of the temperature sensing coil in the temperature sensing film shown according to an embodiment of the present application;

[0034] Figure 3 is a side view and a cross-sectional view of the interdigital electrodes in the temperature sensing film shown according to an embodiment of the present application;

[0035] Figure 4 is a side view and a cross-sectional view of the base column shown according to an embodiment of the present application;

[0036] Figure 5 is a side view and a cross-sectional view of the pressure sensing film shown according to an embodiment of the present application;

[0037] Figure 6 is a flowchart of the preparation method of the flexible sensor shown according to an embodiment of the present application.

[0038] Description of the reference numerals: 10 - temperature sensing film; 11 - temperature sensing coil; 12 - interdigital electrodes; 20 - pressure sensing film; 30 - columnar substrate. Detailed Description of the Embodiments

[0039] The following specific embodiments illustrate the implementation manners of the present application. Those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in this specification.

[0040] In the following description, reference is made to the accompanying drawings, which describe several embodiments of the present application. It should be understood that other embodiments may also be used, and mechanical composition, structure, electrical, and operational changes may be made without departing from the spirit and scope of the present application. The following detailed description should not be considered restrictive. The terms used herein are only for describing specific embodiments and are not intended to limit the present application.

[0041] Although in some instances the terms first, second, etc. are used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another.

[0042] Furthermore, as used herein, the singular forms "a", "an", and "the" are also intended to include the plural forms unless the context indicates otherwise. It should be further understood that the terms "comprising", "including" indicate the presence of the described features, steps, operations, elements, components, items, types, and / or groups, but do not exclude the presence, occurrence, or addition of one or more other features, steps, operations, elements, components, items, types, and / or groups. The terms "or" and "and / or" used herein are interpreted as inclusive, or meaning any one or any combination. Thus, "A, B, or C" or "A, B, and / or C" means "any one of the following: A; B; C; A and B; A and C; B and C; A, B, and C". An exception to this definition occurs only when the combination of elements, functions, steps, or operations is inherently mutually exclusive in some way.

[0043] In recent years, wearable flexible pressure-temperature bimodal sensors have become an important research direction in electronic skin, and they have great application prospects in human perception and human physiological signal monitoring. For intelligent robots, people hope that they can automatically sense information such as pressure and temperature in the surrounding environment and make corresponding analyses and operations based on the obtained information. These sensing functions are the most important ways to achieve robot intelligence, mainly through pressure-temperature sensors. In the aspect of human signal detection, pressure and temperature are important indicators, and pressure-temperature bimodal sensors play an important role. For example, the sensor can be attached to the surface of the human chest to monitor the heart rate, attached to the wrist to detect arterial pulsation and body temperature, attached to the throat to detect vocal cord vibration, and the sensors applied in this aspect not only need to be flexible and have good performance, but also need to meet the characteristics of non-toxic, harmless, and good biocompatibility.

[0044] Therefore, it is of great significance for the development of flexible pressure-temperature sensors to simplify the complexity of devices through the combination of structural design and manufacturing processes and intuitively read multiple tactile signals without involving complex algorithms. For this purpose, the present application proposes a flexible sensor for pressure-temperature dual-mode sensing that can detect circumferential signals and a preparation method thereof. Figure 1 It is a side view and a cross-sectional view of the flexible sensor shown according to an embodiment of the present application. Among them, Figure 1 (a) is a side view of the flexible sensor, Figure 1 (b) is a cross-sectional view of the flexible sensor. As Figure 1 shown, the flexible sensor of the embodiment of the present application includes a temperature sensing film 10 and a pressure sensing film 20 arranged in a stacked manner. A temperature sensing coil 11 is provided on the side of the temperature sensing film 10 away from the pressure sensing film 20, and a plurality of pyramid cone structures are distributed on the side of the pressure sensing film 20 close to the temperature sensing film 10.

[0045] The flexible sensor of the embodiment of the present application includes a temperature sensing film 10 and a pressure sensing film 20, and can realize temperature-pressure dual-mode sensing. As Figure 2 shown, a temperature sensing coil 11 is provided on the temperature sensing film 10. The temperature sensing pattern is prepared by spin-coating photoresist, exposing, and developing on the flexible substrate, and then magnetron sputtering a metal temperature-sensitive material to form the temperature sensing coil 11. In this way, the temperature sensing coil 11 is in the shape of a metal film and is insensitive to pressure, avoiding the coupling of the temperature sensing film 10 with the pressure signal during temperature sensing.

[0046] In one embodiment, the metal temperature-sensitive material used to prepare the temperature sensing coil 11 can be Pt and / or Au. In actual implementation, a layer of Cr can be sputtered on the flexible substrate first as a binder for the temperature-sensitive material and the flexible substrate, and then the metal temperature-sensitive material is sputtered to form the temperature sensing coil 11, so that the metal temperature-sensitive material can be better attached to the flexible substrate.

[0047] As Figure 3 shown, the pressure sensing film 20 adopts a pyramid cone structure, which increases the structural hierarchy in the force direction. As the pressure received by the pressure sensing film 20 increases, the contact area between the pyramid cone and the electrode in the pressure sensing film 20 increases, and the conduction path of the pressure sensing film 20 also increases, enabling a large range of pressure measurement ranges and being able to sense high pressures. In addition, the influence of temperature on the resistance value of the pressure sensing film 20 is much lower than the influence of pressure on the resistance value of the pressure sensing film 20, thereby avoiding the coupling of the pressure sensing film 20 with the temperature signal during pressure sensing.

[0048] In one embodiment, the plurality of pyramid cone structures include pyramid cones of different sizes, and the pyramid cones of different sizes are staggered and evenly distributed. Through the plurality of pyramid cone structures with different heights and widths, as the pressure received by the pressure sensing film 20 increases, the number of contact points between the pyramid cones and the electrodes in the pressure sensing film 20 increases, further increasing the pressure range of the pressure sensing film 20. Of course, the plurality of pyramid cone structures in the pressure sensing film 20 can also be designed to have the same size to improve the sensitivity of the pressure sensing film 20 to detect pressure.

[0049] In one embodiment, the mass of the conductive material in the pressure sensing film 20 accounts for 5% to 15% of the total mass fraction. Here, the flexible substrate material of the pressure sensing film 20 can be PDMS (polydimethylsiloxane), TPU (thermoplastic polyurethane elastomer), PTMC (polytrimethyl carbonate), etc. The conductive material can be carbon nanotubes, graphene, silver nanowires, etc. Preferably, the flexible substrate material is PDMS and the conductive material is carbon nanotubes. Among them, the mass of the carbon nanotubes accounts for 5% to 15% of the total mass fraction. When the mass fraction of the carbon nanotubes is less than 5%, it is difficult for the carbon nanotubes to form a conductive path inside the PDMS, resulting in the obtained pressure sensing film 20 being non-conductive. When the mass fraction of the carbon nanotubes is greater than 15%, the fluidity of the carbon nanotubes and PDMS composite material is poor, and it is difficult to fill the pyramid cone template.

[0050] Please also combine Figure 4 , the side of the temperature sensing film 10 provided with the temperature sensing coil 11 is attached to the columnar substrate 30. The shape of the columnar substrate 30 can be a hollow cylindrical shape as shown in Figure 1 or a solid cylindrical shape as shown in Figure 4 , and its material can be PDMS. The side of the temperature sensing film 10 away from the columnar substrate 30 is provided with interdigital electrodes 12 for measuring the resistance or current change of the pressure sensing film 20. The structure of the interdigital electrodes 12 is as shown in Figure 5 , which is a finger-shaped or comb-shaped periodic electrode pattern. The side of the temperature sensing film 10 provided with the interdigital electrodes 12 is close to the pressure sensing film 20. In this way, the flexible sensor is designed to be columnar, which can sense circumferential pressure and temperature.

[0051] In one embodiment, as an alternative to the interdigital electrodes 12, electrodes can also be provided above and below the pressure sensing film 20 to form a double-layer electrode to measure the resistance or current change of the pressure sensing film 20.

[0052] When preparing a flexible sensor, first, a temperature sensing coil 11 is fabricated on a flexible substrate (such as a PI substrate) using a metal temperature-sensitive material through photolithography and magnetron sputtering. After depositing parylene encapsulation, interdigital pressure electrodes 12 are then prepared by photolithography and magnetron sputtering to obtain a temperature sensing film 10. Next, a pyramid cone template is fabricated using micro-nano processing techniques such as microsphere self-assembly, RIE reactive ion etching, magnetron sputtering, and wet etching of silicon. A pressure-sensitive material mixture of PDMS and carbon nanotubes CNTs is poured into the pyramid cone template and spin-coated. After heating and curing, the film and the template are peeled off to obtain a pressure sensing film 20 with a hierarchical pyramid cone structure. The temperature sensing film 10 and the pressure sensing film 20 are sequentially pasted on a columnar substrate 30, and finally, parylene is deposited for encapsulation to obtain the flexible sensor.

[0053] The flexible sensor of the present application includes a temperature sensing film and a pressure sensing film arranged in a stacked manner. A temperature sensing coil is provided on a side of the temperature sensing film away from the pressure sensing film, and a plurality of pyramid cone structures are distributed on a side of the pressure sensing film close to the temperature sensing film. The present application forms a flexible sensor with pressure-temperature dual-mode sensing through the temperature sensing film and the pressure sensing film.

[0054] Second Embodiment

[0055] Figure 6 is a schematic flow chart of a method for preparing a flexible sensor according to an embodiment of the present application. As Figure 6 shown, an embodiment of the present application also proposes a method for preparing a flexible sensor, including the following steps:

[0056] S1: Form a temperature sensing coil on a flexible substrate to obtain a temperature sensing film.

[0057] In one embodiment, step S1 includes:

[0058] Sputter a temperature-sensitive material on a flexible substrate to form a temperature sensing coil;

[0059] Encapsulate the temperature sensing coil to form a first encapsulation layer;

[0060] Form interdigital electrodes on the first encapsulation layer to obtain a temperature sensing film.

[0061] Here, a PMMS sacrificial layer is spin-coated on a clean silicon wafer. After curing at 110°C - 180°C, a 15% PI solution is spin-coated and cured at 80°C - 250°C to serve as a flexible substrate. Then, photoresist is spin-coated, exposed, and developed to prepare a temperature sensing pattern. Cr and Pt (or Au) are magnetron sputtered in sequence. After sputtering, the silicon wafer is immersed in an NMP (N-methylpyrrolidone) solution to remove the remaining photoresist, and the Cr and Pt on the remaining photoresist are removed together, leaving only the Cr and Pt of the temperature sensing coil. It should be noted that the NMP solution is a solution formed by dissolving N-methylpyrrolidone (NMP) in water or other organic solvents. Chemical Vapor Deposition (CVD) is used to deposit a layer of parylene (or a layer of PI is spin-coated) to encapsulate the temperature sensing film. Then, photoresist is spin-coated, exposed, developed, and an electrode pattern for the pressure sensing film is prepared. Cr and Au are magnetron sputtered. After sputtering, the silicon wafer is immersed in the NMP solution to remove the remaining photoresist and the Cr and Au on the photoresist, leaving only the electrode pattern of the pressure sensing film. The entire silicon wafer is covered with a PDMS film, leaving only the pad part of the temperature sensing coil exposed. Reactive Ion Etching (RIE) is used to remove the parylene at the pad part of the temperature sensing coil, exposing the Cr / Pt material for convenient subsequent circuit connection.

[0062] S2: Provide a pyramid cone structure template.

[0063] In one embodiment, step S2 includes:

[0064] Form a microsphere film through a microsphere self-assembly process;

[0065] Etch the microspheres in the microsphere film to make them smaller and form a mask template on the microsphere film;

[0066] Place the mask template on the substrate and perform anisotropic etching on the substrate to prepare a pyramid cone structure template.

[0067] Here, a monolayer film composed of mixed microspheres with different diameters is prepared on a silicon wafer substrate by using the capillary force between microspheres through the microsphere self-assembly process. After the microspheres are etched smaller by reactive ion etching, a Cr metal layer with a thickness of 50 nm to 100 nm is deposited by magnetron sputtering. The material can be polystyrene (PS). Then, the microspheres are removed using tape or organic solvents. The organic solvents can be acetone, chloroform, xylene, toluene, etc. In this way, a Cr metal layer can be formed on the silicon wafer substrate, and multiple small holes with different pore diameters are distributed on this metal layer, which can be used as a mask template in subsequent processes. Next, a wet etching process of silicon is adopted, and the silicon wafer is anisotropically etched using an alkaline solution. Since the diameters of the Cr holes on the silicon wafer are different, that is, the areas of the silicon wafer exposed to the etching solution are different, the etched pits on the silicon wafer are in the shape of inverted pyramid cones, and the widths and depths of each inverted pyramid cone are different, with a size range of 1 μm to 200 μm. The center distance between each inverted pyramid cone is 1 μm to 500 μm.

[0068] To prepare a silicon wafer template with a hierarchical pyramid cone structure, it is necessary to limit the diameter ratio of the microspheres and the volume ratio of the stock solutions of microspheres with different diameters. First, the diameter ratio of the microspheres does not exceed 4. If the diameter ratio of the microspheres is too large, the small microspheres may aggregate between the large microspheres or arrange on the surface of the large microspheres and thus cannot form a monolayer film, which will affect the integrity of the small holes on the mask template and thus cannot form a hierarchical inverted pyramid cone structure. If the diameter ratio of the microspheres is close to 1, the prepared hierarchical pyramid cone structure lacks an obvious height difference. It is preferable to mix microspheres with a diameter ratio of about 2, such as mixing 1-μm and 2-μm microspheres, or mixing 20-μm, 30-μm, and 40-μm microspheres. Secondly, the volume ratio of the stock solutions of microspheres used to prepare microspheres with different diameters affects the quantity ratio of microspheres with different diameters formed, and thus affects the mixing uniformity of the microspheres. The stock solution of microspheres refers to a suspension containing microspheres of a specific size. If the volume ratio of the stock solutions of microspheres is too large or too small, it will lead to an imbalance in the number of large and small microspheres, and the number of microspheres of a certain diameter is relatively large and aggregates locally, reducing the distribution uniformity of Cr holes with different diameters and affecting the distribution uniformity of the hierarchical pyramid cone structure, and further affecting the stability of the pressure sensor performance. Preferably, the volume ratio of the stock solutions of microspheres of different sizes is between 1:1 and 8:1. For example, the volume ratio of the microsphere suspension is 20-μm microsphere stock solution: 30-μm microsphere stock solution: 40-μm microsphere stock solution = 1:2:4. In this way, microspheres with different diameters are evenly distributed, ensuring the distribution uniformity of the hierarchical pyramid cone structure and improving the stability of the pressure sensing performance of the flexible sensor.

[0069] In one embodiment, forming a microsphere film by the microsphere self-assembly process includes:

[0070] Providing a silicon wafer and performing a hydrophilic treatment on the silicon wafer;

[0071] Place the silicon wafer obliquely, and extrude the microsphere suspension along the silicon wafer from the higher side of the silicon wafer, so that the microsphere suspension diffuses on the surface of the silicon wafer to form microspheres;

[0072] Place the silicon wafer in plasma water, so that the microspheres on the silicon wafer float and disperse on the water surface;

[0073] Add sodium dodecyl sulfate solution to the plasma water, so that the microspheres on the water surface aggregate into a film to obtain a microsphere film.

[0074] Here, the specific steps of the microsphere self-assembly process are as follows:

[0075] Put a silicon wafer into a mixed solution of ammonia water: hydrogen peroxide: deionized water = 1:2:6 and heat it to 150 °C for 10 min for hydrophilic treatment, then wash it repeatedly with clean water and dry it. Mix the microsphere suspension in proportion and add absolute ethanol at a ratio of 1:1.2, and then ultrasonically treat the mixed microsphere suspension for 10 min. Set the silicon wafer to be inclined at about 45 degrees, and use a pipette to extrude the ultrasonically treated microsphere suspension along the silicon wafer from the higher side of the silicon wafer, so that the liquid flows down along the silicon wafer and naturally diffuses on the surface of the silicon wafer. After the silicon wafer is inclined to about 30 degrees, slowly and uniformly place it into a container filled with plasma water, so that the microspheres on the silicon wafer float and disperse at the water-air interface. Drop 2 drops of 10% SDS (sodium dodecyl sulfate) solution into the water at the edge of the container, so that the microspheres on the water surface aggregate into a film. Use tweezers to hold a clean single-crystalline silicon wafer at an inclination of about 45 degrees to lift the microsphere film from the water surface, or place the silicon wafer at the bottom of the water container, and use a peristaltic pump to pump out the water so that the microsphere film on the water surface naturally falls on the silicon wafer as the water level drops.

[0076] The specific steps of ion reaction etching are as follows:

[0077] Use O2 as the etching gas. The etching power and time are determined by the microsphere diameter, and the microspheres can be etched to be non-connected to each other. The larger the microsphere diameter, at least one of the etching power and the etching time should be increased. For example, for a mixed microsphere of 20 μm, 30 μm, and 40 μm, the etching power is 200 W and the etching time is 20 min.

[0078] The wet etching of silicon uses NaOH or KOH solution heated to 80℃~90℃ for etching, and the etching time is 5min~60min. The specific etching time is determined by the Cr pore diameter and the concentration of the etching solution. The larger the pore size and the smaller the concentration of the etching solution, the longer the etching time. For example, using Aladdin (S128515) sodium hydroxide standard solution, the mixed microspheres of 1μm and 2μm are etched at 80℃ for about 5min, and the mixed microspheres of 20μm, 30μm, and 40μm are etched at 80℃ for about 50min~60min. In order to smoothly carry out the subsequent demolding, the surface of the silicon template needs to be hydrophobically treated after etching, using a demolding agent or placing it in a sealed trimethylchlorosilane environment for 15min. The hydrophobically treated silicon template can be reused.

[0079] S3: Passing a mixture of conductive material and polymer material through a pyramid-cone structure template to prepare a pressure sensing film having a plurality of pyramid-cone structures on one side.

[0080] In one embodiment, step S3 comprises:

[0081] Adding a conductive material to a polymer material precursor and mixing them evenly to obtain a mixture;

[0082] The mixture was spin-coated on a pyramid-cone structure template;

[0083] The mixture is cured and demolded to obtain a pressure sensing film with a plurality of pyramid cone structures on one side.

[0084] Here, materials with good biocompatibility are selected for preparing flexible conductive films, such as PDMS (polydimethylsiloxane), TPU (polyurethane elastomer), PTMC (polytrimethyl carbonate), etc. Since PDMS has the best biocompatibility and thermal stability, PDMS is preferred. The conductive material is dispersed in an organic solvent, and the conductive material can be carbon nanotubes, graphene, silver nanowires, etc., and the most commonly used carbon nanotubes are preferred. The organic solution can be tetrahydrofuran, n-hexane, cyclohexane, preferably tetrahydrofuran. PDMS main liquid is added to the organic solution, the mixture is stirred evenly, and then heated in a water bath to volatilize the organic solution, and then a curing agent is added and stirred again to mix evenly.

[0085] Carbon nanotubes are added to the PDMS monomer, where the mass of the carbon nanotubes accounts for 5% - 15% of the total mass fraction. When the mass fraction of the carbon nanotubes is less than 5%, it is difficult for the carbon nanotubes to form a conductive path inside the PDMS, resulting in the obtained flexible film being non-conductive. When the mass fraction of the carbon nanotubes is greater than 15%, the fluidity of the carbon nanotube and PDMS composite material is poor, and it is difficult to fill the hierarchical pyramid cone template. Then, the PDMS monomer and the curing agent are mixed evenly at a ratio of 10:1. The obtained mixture is degassed and then spin-coated on the silicon template and cured at 25°C - 150°C for 0.25 h - 24 h. When the curing temperature is less than 25°C, the curing time required is longer, affecting the forming efficiency of the flexible film. As the curing temperature increases, the curing speed is faster and the time is shorter. When the curing temperature is greater than 150°C, the reaction is too fast, and the small molecules generated during the curing process do not have time to diffuse out, easily forming a honeycomb structure. The curing time is closely related to the curing temperature. Increasing the curing temperature has the same effect as reducing the curing time. The curing time is determined to be 0.25 h - 24 h according to the curing temperature range. Finally, the cured conductive material is peeled off from the silicon template to obtain a conductive pressure-sensitive film with a pyramid cone structure on the surface.

[0086] S4: Assemble the temperature sensing film and the pressure sensing film, with the side of the temperature sensing film having the temperature sensing coil away from the pressure sensing film and the side of the pressure sensing film having multiple pyramid cone structures close to the temperature sensing film to obtain a flexible sensor.

[0087] Here, the temperature sensing film is pasted onto the columnar substrate, and the temperature sensing coil side of the temperature sensing film is close to the columnar substrate. The side of the pressure sensing film having the hierarchical pyramid cone structure is attached to the temperature sensing film. The temperature sensing pad and the pressure sensing pad are pasted with a PDMS film, and then a layer of parylene is deposited for insulation packaging. Finally, the PDMS film at the pad part is removed.

[0088] The preparation method of the flexible sensor according to the embodiment of the present application includes: forming a temperature sensing coil on a flexible substrate to obtain a temperature sensing film; providing a pyramid cone structure template; passing a mixture of a conductive material and a polymer material through the pyramid cone structure template to prepare a pressure sensing film with multiple pyramid cone structures on one side; assembling the temperature sensing film and the pressure sensing film, with the side of the temperature sensing film having the temperature sensing coil away from the pressure sensing film and the side of the pressure sensing film having multiple pyramid cone structures close to the temperature sensing film to obtain a flexible sensor. A flexible sensor with pressure-temperature dual-mode sensing is formed through the temperature sensing film and the pressure sensing film.

[0089] The third embodiment

[0090] The embodiments of the present application also propose a preparation method for a flexible sensor, including the following steps:

[0091] (1) After rinsing the silicon wafer successively with anhydrous ethanol and deionized water and drying it, spin-coat PMMA as a sacrificial layer at a speed of 3500 rpm, bake it at 110 °C for 5 min, 150 °C for 5 min, and 180 °C for 10 min. Degas the 15% PI solution in vacuum for 30 min, spin-coat it on the cured PMMA silicon wafer at a speed of 3500 rpm, and bake it at 80 °C, 120 °C, 150 °C, 180 °C, 200 °C, 220 °C, and 250 °C successively for 20 min to cure the PI. Spin-coat photoresist at a speed of 3500 rpm, bake it at 100 °C for 3 min, photolithograph the temperature sensing pattern, soak it in the developer for 1 min until the photolithographic pattern appears, and the pattern line width is 150 μm.

[0092] Magnetron sputter Cr 50 nm and Pt 300 nm. Immerse the sputtered silicon wafer in NMP until the non-patterned parts of Cr and Pt are completely lifted off, and use ultrasonic cleaning for 5 min to assist in lifting off. Deposit 2 μm of parylene insulation encapsulation on the temperature-sensitive pattern using chemical vapor deposition (CVD). Then, spin-coat photoresist at a speed of 3500 rpm, bake it at 100 °C for 3 min, photolithograph the pressure electrode, and soak it in the developer for 1 min until the pressure electrode pattern appears. Magnetron sputter Cr 50 nm and Au 300 nm. Immerse the sputtered silicon wafer in NMP until the non-patterned parts of Cr and Au are completely lifted off, and use ultrasonic cleaning for 5 min to assist in lifting off. Cover the non-temperature sensing pad part with a PDMS film, and use reactive ion etching (RIE) with an oxygen flux of 100 sccm, a power of 100 W, and an etching time of 20 min to remove the 2-μm-thick parylene above the pad, exposing the Pt for convenient wiring.

[0093] (2) Mix PS (polystyrene) microspheres with diameters of 20 μm, 30 μm, and 40 μm in a ratio of 1:2:4. Add anhydrous ethanol in an amount 1.2 times the volume of the mixed solution and sonicate for 10 min. Use a pipette to drop the mixed solution onto a hydrophilized silicon wafer. After the diffusion is uniform, slowly place the silicon wafer into water, then add two drops of 2% SDS solution to form a dense PS microsphere film on the water surface. Then use a (110) silicon wafer to pick up the microsphere film on the water surface, and heat it flat at 60 °C for 1 min until the water evaporates completely. Use O2 of RIE to etch the microspheres on the silicon wafer, with a gas flux of 100 sccm, a power of 100 W, and a time of 20 min to 40 min. It is okay when the microspheres are observed to be etched smaller and obvious gaps appear between the microspheres under a microscope. Then use magnetron sputtering to deposit 50 nm thick Cr on the silicon wafer with microspheres, and then use tape or organic solution to remove the microspheres. Heat the NaOH standard titrant to 80 °C and place the silicon wafer with Cr holes into it for corrosion for 20 - 40 min. It is okay when the holes are clearly observed to be corroded into squares with appropriate sizes under a microscope, completing the preparation of the hierarchical pyramid cone etching pits. Use a release agent or seal in an environment of trimethylchlorosilane and place it for 15 min to treat the corroded silicon wafer to make its surface hydrophobic.

[0094] (3) Weigh 0.1 g of carbon nanotubes and 5 g of tetrahydrofuran solution into a glass sample bottle, sonicate for 30 min, stir magnetically or mechanically for 1 h. Weigh 1 g of polydimethylsiloxane (PDMS) prepolymer into the sample bottle and continue to stir and mix evenly. At the same time, heat in a water bath at 70 °C to volatilize tetrahydrofuran. Then measure 0.1 g of curing agent and add it to the sample bottle, stir evenly at room temperature, and place it under a vacuum condition of 0.1 Torr for 30 min to remove air bubbles. Spin-coat the above mixed solution on the prepared silicon wafer hierarchical pyramid microstructural template at a rotation speed of 1000 rpm for 30 s, and cure it at 60 °C. Then peel it off from the template. The thickness of the conductive film is about 200 μm, and the height of the first layer of pyramid cone microstructures is between 5 - 20 μm.

[0095] (4) Paste the temperature sensing film onto the columnar PDMS with PDMS double-sided tape, with the pressure electrode facing outwards. Then paste the side with the pyramid cone structure of the prepared pressure sensitive film facing inwards on the pressure electrode, use a PDMS film to cover the temperature sensing pad and pressure sensing pad parts, then deposit 2 μm thick parylene insulation encapsulation by CVD. Finally, remove the PDMS film covering the pad parts to expose the temperature sensing pad and pressure sensing pad.

[0096] Fourth Embodiment

[0097] The difference between this embodiment and the third embodiment is that Au is used as the metal temperature sensitive material.

[0098] Fifth Embodiment

[0099] The difference between this embodiment and the third embodiment is that a spin coating PI encapsulation method is adopted.

[0100] Sixth Embodiment

[0101] The difference between this embodiment and the third embodiment is that microspheres with a diameter of 20 μm are used.

[0102] The above embodiments are only illustrative of the principles and effects of the present application, and are not used to limit the present application. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed in the present application should still be covered by the claims of the present application.

Claims

1. A flexible sensor, characterized in that, It includes a temperature sensing thin film and a pressure sensing thin film arranged in a stacked manner. A temperature sensing coil is provided on the side of the temperature sensing thin film away from the pressure sensing thin film, and a plurality of pyramid cone structures are distributed on the side of the pressure sensing thin film close to the temperature sensing thin film.

2. The flexible sensor according to claim 1, wherein, Interdigitated electrodes are provided on the side of the temperature sensing thin film close to the pressure sensing thin film.

3. The flexible sensor according to claim 1, characterized in that, The flexible sensor further includes a columnar substrate, and the side of the temperature sensing thin film with the temperature sensing coil is close to the columnar substrate.

4. The flexible sensor according to claim 1, wherein, Among the plurality of pyramid cone structures, there are pyramid cones of different sizes.

5. The flexible sensor according to claim 1, characterized in that, The mass fraction of the conductive material in the pressure sensing thin film accounts for 5% - 15% of the total mass.

6. A preparation method of a flexible sensor, characterized in that, It includes the following steps: S1. Form a temperature sensing coil on a flexible substrate to obtain a temperature sensing thin film; S2. Provide a pyramid cone structure template; S3. Pass a mixture of a conductive material and a polymer material through the pyramid cone structure template to prepare a pressure sensing thin film with a plurality of pyramid cone structures on one side; S4. Assemble the temperature sensing thin film and the pressure sensing thin film, such that the side of the temperature sensing thin film with the temperature sensing coil is away from the pressure sensing thin film, and the side of the pressure sensing thin film with a plurality of pyramid cone structures is close to the temperature sensing thin film, to obtain a flexible sensor.

7. The method according to claim 6, wherein The step S1 includes: Sputter a temperature sensitive material on a flexible substrate to form a temperature sensing coil; Encapsulate the temperature sensing coil to form a first encapsulation layer; Form interdigitated electrodes on the first encapsulation layer to obtain a temperature sensing thin film.

8. The method according to claim 6, characterized in that, The step S2 includes: Form a microsphere thin film through a microsphere self-assembly process; Etch the microspheres in the microsphere thin film to become smaller, and form a mask template on the microsphere thin film; Place the mask template on a substrate and perform anisotropic etching on the substrate to prepare a pyramid cone structure template.

9. The method according to claim 8, wherein The forming of the microsphere thin film through the microsphere self-assembly process includes: Provide a silicon wafer and perform a hydrophilic treatment on the silicon wafer; Place the silicon wafer obliquely, and extrude a microsphere suspension from the higher side of the silicon wafer along the silicon wafer, so that the microsphere suspension diffuses on the surface of the silicon wafer to form microspheres; Place the silicon wafer in plasma water, so that the microspheres on the silicon wafer float and disperse on the water surface; Add a sodium dodecyl sulfate solution to the plasma water to make the microspheres on the water surface aggregate into a film to obtain a microsphere thin film.

10. The method according to claim 6, characterized in that, The step S3 includes: Add a conductive material to a polymer material precursor and mix evenly to obtain a mixture; Spin-coat the mixture on the pyramid cone structure template; Perform a curing and demolding treatment on the mixture to obtain a pressure sensing thin film with a plurality of pyramid cone structures on one side.

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