Preparation method of flexible pressure sensor and flexible pressure sensor

Abstract

The invention discloses a preparation method of a flexible pressure sensor and the flexible pressure sensor, and the preparation method of the flexible pressure sensor comprises the steps: employing femtosecond laser to etch a multi-level microstructure on the upper surface of a mold substrate, and obtaining a transfer mold; copying the multi-level microstructure on the upper surface of the transfer mold to the upper surface of a flexible substrate through compression molding to obtain a flexible multi-level substrate; preparing a conductive material layer on the upper surface of the flexible multi-level substrate to obtain a first conductive flexible substrate and a second conductive flexible substrate; and overlapping the first conductive flexible substrate and the second conductive flexible substrate, and performing sealing treatment to obtain the flexible pressure sensor. According to the invention, a laser processing and compression molding composite method is adopted, so that the morphology precision of the microstructure and the consistency of the array are ensured, the batch production of the flexible multi-level microstructure substrate is realized, the preparation cost of the flexible substrate is greatly reduced, and the large-scale production of the flexible sensor is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible sensor production, and in particular to a preparation method of a flexible pressure sensor and the flexible pressure sensor. Background Art

[0002] With the rapid development of digitalization and the digital economy, sensor design, manufacturing, and applications have garnered widespread attention. Flexible pressure sensors offer irreplaceable advantages in biomedical health monitoring, such as pulse monitoring, respiratory rate detection, and vocal cord signal acquisition. As a new generation of high-performance sensors, flexible pressure sensors operate by detecting pressure changes in real time and converting them into electrical signals. These sensors are widely used in smart wearable devices, biomedical health monitoring, intelligent robotics, and electronic skin.

[0003] The performance parameters of flexible sensors, such as sensitivity, pressure detection range, and response time, are key factors that determine their application value. Relevant research has shown that the introduction of micro-nanostructures in the structural design of sensors can improve the overall performance of sensors, and as the complexity of the micro-nanostructures increases, the detection range and sensitivity of the sensors will also be further improved. At present, the preparation of microstructures on sensor substrates often adopts processing techniques such as electrospinning, 3D printing, and screen printing. Although the above processes can produce flexible sensor substrates with certain performance, their preparation methods all involve reciprocating processing of a single substrate. Often, the more complex the substrate microstructure, the more complicated the entire process procedure, resulting in low production efficiency and high costs, which is not conducive to the industrial-grade mass production of flexible sensor substrates.

[0004] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0005] In view of the above-mentioned deficiencies in the prior art, the purpose of the present invention is to provide a method for preparing a flexible pressure sensor and a flexible pressure sensor, which are used to solve the technical problems that the manufacturing process of the micro-nano structure on the substrate of the existing flexible pressure sensor is complex, time-consuming, and not conducive to large-scale production.

[0006] The technical solutions of the present invention are as follows: In a first aspect, the present invention provides a method for preparing a flexible pressure sensor, comprising: A femtosecond laser is used to etch a multi-level microstructure on the upper surface of the mold substrate to obtain a transfer mold; replicating the multi-level microstructure on the upper surface of the transfer mold onto the upper surface of the flexible substrate by compression molding to obtain a flexible multi-level substrate having a multi-level microstructure; Preparing a conductive material layer on the upper surface of the flexible multi-level substrate to obtain a first conductive flexible substrate and a second conductive flexible substrate, wherein the upper surface of the first conductive flexible substrate has a first conductive material layer, and the upper surface of the second conductive flexible substrate has a second conductive material layer; overlapping the upper surface of the first conductive flexible substrate and the upper surface of the second conductive flexible substrate to form an interlocking structure; The first conductive flexible substrate and the second conductive flexible substrate that are stacked are sealed to obtain the flexible pressure sensor.

[0007] In a further embodiment of the present invention, the step of etching a multi-level microstructure on the upper surface of the mold substrate using a femtosecond laser to obtain a transfer mold comprises: A femtosecond laser is used to etch a microporous structure array on the upper surface of the transfer mold, wherein the microporous structure array is arranged in a square array; A femtosecond laser is used to etch a trapezoidal groove structure on the upper surface of the transfer mold, wherein the two ends of the trapezoidal groove structure are respectively connected to the micropore structures in adjacent rows or connected columns, and the micropore structure is located at the intersection of the trapezoidal groove structures; the surfaces of the micropores and the trapezoidal groove structure have irregular micro-nano structures after femtosecond laser induction.

[0008] A further configuration of the present invention is that the multi-level microstructure on the upper surface of the transfer mold is replicated onto the upper surface of the flexible substrate by compression molding to obtain a flexible multi-level substrate having a multi-level microstructure, comprising: A compression molding device is provided, comprising a punch and a holding structure, wherein the punch has a cavity for accommodating the transfer mold; the punch is movable in a vertical direction; the holding structure has a cavity for accommodating the flexible substrate, and the cavity of the holding structure for accommodating the flexible substrate is arranged opposite to the cavity of the punch for accommodating the transfer mold; securing the flexible substrate within the cavity of the retaining structure; The punch and the transfer mold are controlled to move downward so as to press the flexible substrate against the punch and deform it, thereby forming the flexible substrate to obtain a flexible multi-level substrate with a multi-level microstructure on the upper surface; the microporous structure on the upper surface of the transfer mold is transferred into micropillars on the upper surface of the flexible multi-level substrate, the trapezoidal groove structure on the upper surface of the transfer mold is transferred into reinforcing ribs on the upper surface of the flexible multi-level substrate, and irregular micro-nano structures are transferred on the surfaces of the micropillars and the reinforcing ribs.

[0009] A further configuration of the present invention is to overlap the upper surface of the first conductive flexible substrate and the upper surface of the second conductive flexible substrate to form an interlocking structure, and encapsulate the flexible pressure sensor, including: Welding and fixing the wire on the upper surface of the first conductive flexible substrate or the second conductive flexible substrate; placing upper surfaces of a first conductive flexible substrate and a second conductive flexible substrate facing each other, forming an interlocking structure between the first conductive flexible substrate and the second conductive flexible substrate; The stacked first conductive flexible substrate and the second conductive flexible substrate are sealed.

[0010] According to a further configuration of the present invention, the compression molding device is a single-station device, the compression molding temperature of the compression molding device is 170°C, the compression pressure is 500 N, and the total compression time is 400 s.

[0011] In a further configuration of the present invention, the microporous structure is in the shape of a regular quadrangular prism, the depth of the microporous structure is 100 μm, and the top surface size is 100×100 μm. 2 , the bottom surface size is 80×80 μm 2 The spacing between each micropore is 300 μm; the cross-section of the trapezoidal groove structure is a regular trapezoid, the depth of the trapezoidal groove structure is less than the depth of the micropore structure, the upper side length of the trapezoidal groove structure is 60 μm, and the lower side length is 50 μm.

[0012] According to a further configuration of the present invention, the transfer mold adopts a titanium alloy substrate, and the titanium alloy substrate adopts a TC4 titanium alloy element ratio.

[0013] In the second aspect, some preferred embodiments of the present invention also provide a flexible pressure sensor, which is obtained by the above-mentioned method for preparing the flexible pressure sensor; the flexible pressure sensor includes: a first conductive flexible substrate, a first conductive material layer, a second conductive flexible substrate, a second conductive material layer and a metal wire; wherein, the upper surface of the first conductive flexible substrate and the upper surface of the second conductive flexible substrate respectively have a multi-level microstructure, the upper surface of the first conductive flexible substrate and the upper surface of the second conductive flexible substrate are abutted against each other, the first conductive material layer is located at the upper surface of the first conductive flexible substrate, and the second conductive material layer is located at the upper surface of the second conductive flexible substrate.

[0014] In a further embodiment of the present invention, the multi-level microstructure includes a first microstructure layer, a second microstructure layer, and a third microstructure layer. The first microstructure layer comprises a micropillar array arranged in a square array, the second microstructure layer comprises reinforcing ribs, the ends of the reinforcing ribs being connected to the micropillars, and the micropillars being located at the intersection of the reinforcing ribs. The third microstructure layer comprises irregular micro-nanostructures disposed on the surfaces of the micropillar array and the reinforcing ribs. When the upper surface of the first conductive flexible substrate and the upper surface of the second conductive flexible substrate are in contact, the micropillars on the upper surface of the first conductive flexible substrate are located in the accommodation spaces between the reinforcing ribs of the second conductive flexible substrate, and the micropillars on the upper surface of the second conductive flexible substrate are located in the accommodation spaces between the reinforcing ribs of the first conductive flexible substrate.

[0015] According to a further configuration of the present invention, the microcolumns are in the shape of regular quadrangular pyramids, and the cross-section of the reinforcing ribs is trapezoidal.

[0016] The present invention discloses a method for preparing a flexible pressure sensor and a flexible pressure sensor, wherein the method for preparing the flexible pressure sensor comprises: etching a multi-level microstructure on the upper surface of a mold base using a femtosecond laser to obtain a transfer mold; replicating the multi-level microstructure on the upper surface of the transfer mold to the upper surface of a flexible substrate by compression molding to obtain a flexible multi-level substrate, wherein the flexible multi-level substrate has a multi-level microstructure; preparing a conductive material layer on the upper surface of the flexible multi-level substrate to obtain a first conductive flexible substrate and a second conductive flexible substrate, wherein the upper surface of the first conductive flexible substrate has a first conductive material layer, and the upper surface of the second conductive flexible substrate has a second conductive material layer; overlapping the upper surface of the first conductive flexible substrate and the upper surface of the second conductive flexible substrate to form an interlocking structure; and sealing the overlapped first conductive flexible substrate and the second conductive flexible substrate to obtain the flexible pressure sensor. The present invention prepares a transfer mold with a multi-level microstructure array through femtosecond laser processing, and performs precision molding through the transfer mold, thereby simplifying the processing procedure of the flexible sensor, improving the precision processing efficiency of the multi-level microstructure, greatly reducing the preparation cost of the mold, and improving the industrial-level batch production efficiency of the flexible sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary personnel in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0018] Figure 1 It is a schematic flow chart of the method for preparing the flexible pressure sensor of the present invention.

[0019] Figure 2 It is a process flow chart of the preparation method of the flexible pressure sensor in the present invention.

[0020] Figure 3 It is a flexible multi-level substrate with a multi-level microstructure in the present invention.

[0021] Figure 4 This invention Figure 3 Schematic cross-sectional view along the direction of the arrow.

[0022] Figure 5 This is a surface morphology image of a transfer mold prepared by the method for preparing a flexible pressure sensor in the present invention under a microscope.

[0023] Figure 6 This is a surface morphology image of a flexible multi-level substrate prepared by the method for preparing a flexible pressure sensor in the present invention under a microscope.

[0024] Figure 7 It is a structural schematic diagram of the flexible pressure sensor in the present invention.

[0025] Figure 8 It is a state schematic diagram of the flexible pressure sensor in the present invention.

[0026] The symbols in the accompanying drawings are: 1. flexible multi-level substrate; 11. first conductive flexible substrate; 12. second conductive flexible substrate; 2. micro-pillars; 3. reinforcing ribs. DETAILED DESCRIPTION

[0027] The present invention provides a method for preparing a flexible pressure sensor and a flexible pressure sensor. To clarify the objectives, technical solutions, and effects of the present invention, the present invention is further described below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are intended only to illustrate the present invention and are not intended to limit the present invention.

[0028] In the embodiments and patent claims, unless otherwise specified herein, the words "a," "an," "the," and "the" may include plural forms. If the embodiments of the present invention include descriptions of "first," "second," etc., such descriptions are for descriptive purposes only and should not be understood as indicating or implying their relative importance or implicitly specifying the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include at least one of such features.

[0029] It should be further understood that the term "comprising" as used in the description of the present invention refers to the presence of the stated features, integers, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof. It should be understood that when we refer to an element as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element, or there can be intermediate elements. In addition, "connected" or "coupled" as used herein can include wireless connections or wireless couplings. The term "and / or" as used herein includes all or any units and all combinations of one or more associated listed items.

[0030] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with their meanings in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless specifically defined as herein.

[0031] In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the fact that ordinary technicians in this field can implement them. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0032] The applicant's research has found that the introduction of micro-nanostructures into sensor design can significantly improve the overall performance of existing technologies, particularly sensor sensitivity. The fabrication process for flexible sensors focuses on two key areas: ensuring high-quality fabrication of the flexible sensor substrate to ensure performance; and minimizing costs and cycle time while ensuring performance. Currently, mainstream micro-nanostructures for sensors include micro-pyramid arrays, micro-sphere arrays, micro-pillar arrays, and corrugated morphologies. These arrays can enhance sensitivity by increasing contact area and, by leveraging pressure-dispersing properties, increase the sensor's detection range. However, these simple structures offer limited performance improvements and are insufficient to meet the demands of high-performance flexible sensor measurements. Therefore, to further enhance the sensor's detection range and sensitivity, more complex structures, such as multi-layer composite structures or interlocking structures, can be introduced onto the sensor substrate surface to further disperse pressure. Currently, commonly used fabrication techniques, such as electrospinning, 3D printing, and screen printing, are complex and insufficient for large-scale production. To improve sensor performance, new, efficient and cost-effective fabrication methods are urgently needed.

[0033] Therefore, in response to the above problems, Figure 1 and Figure 2 As shown, in some preferred embodiments of the present invention, a method for preparing a flexible pressure sensor is provided, which includes: S10, etching a multi-level microstructure on the upper surface of the mold substrate using a femtosecond laser to obtain a transfer mold; It is understood that the multi-level microstructure refers to a complex structural system within a material or substance, composed of ordered or disordered combinations of microscopic structural units of varying scales and levels. These structural units exhibit a distinct spatial hierarchy, and the interrelationships and interactions between the various levels determine the material's macroscopic properties, thereby improving the performance of the flexible pressure sensor. The mold substrate is made of one of titanium alloy, stainless steel, ceramic, and glass. Preferably, the transfer mold utilizes a titanium alloy substrate, employing a TC4 titanium alloy elemental composition with a titanium content of 88.3%-90%, an aluminum content of 5.5%-6.75%, and a vanadium content of 3.5%-4.5%. Other impurities (such as iron, oxygen, carbon, and nitrogen) are less than 0.4%. The femtosecond laser scanning speed is 400 mm / s, the laser power is 3 W, and the laser frequency is 290 kHz. The femtosecond laser etching method and process are prior art and will not be further described here.

[0034] Further, see Figure 5 , the transfer mold is as follows Figure 5 As shown in a in FIG. Since the transfer mold is used to replicate the microstructure onto the upper surface of a flexible substrate to obtain a flexible multi-level substrate, the etched transfer mold is obtained by inverting the multi-level microstructure on the upper surface of a conductive flexible substrate with a predetermined structure. The method of etching the multi-level microstructure on the upper surface of the mold substrate using a femtosecond laser to obtain the transfer mold includes: S11, etching a microporous structure array on the upper surface of the transfer mold, wherein the microporous structure array is arranged in a square array; Please also refer to Figure 5 b and Figure 5 In the c, Figure 5 b in the figure represents the multi-level microstructure array on the upper surface of the transfer mold. Figure 5 The c in the figure represents a microporous structure in a multi-level microstructure array. The microporous structure is in the shape of an inverted square prism, has a depth of 100 μm, and the size of the micropore opening, i.e., the top surface, is 100×100 μm. 2 , the bottom surface size of the microwell is 80×80μm 2 The spacing between each micropore is 300 μm; the micropore structure is obtained by femtosecond laser scanning 60 times, and the micropore etching effect is improved by repeated laser etching processing with femtosecond laser.

[0035] S12. A trapezoidal groove structure is etched on the upper surface of the transfer mold using a femtosecond laser, wherein both ends of the trapezoidal groove structure are respectively connected to the micropore structures in adjacent rows or connected columns, and the micropore structure is located at the intersection of the trapezoidal groove structures; the surfaces of the micropores and the trapezoidal groove structure have an irregular micro-nano structure after femtosecond laser induction.

[0036] Please also refer to Figure 5 b and Figure 5 In d, Figure 5 b in the figure is the multi-level microstructure array on the upper surface of the transfer mold. Figure 5 The d in the figure represents the trapezoidal groove structure in the multi-level microstructure array. The depth of the trapezoidal groove structure is less than the depth of the microporous structure, and the cross-section of the trapezoidal groove structure is a regular trapezoid. The upper side length of the cross-section of the trapezoidal groove structure is 60 μm, and the lower side length is 50 μm. The trapezoidal groove structure is obtained by scanning the femtosecond laser 12 times, and the micropore etching effect is improved by repeated laser etching processing with the femtosecond laser. It should be noted that in this application, the micropore structure and the trapezoidal groove structure are etched in two steps using a femtosecond laser in sequence, which can also be replaced by etching the trapezoidal groove structure and the microporous structure in sequence using a femtosecond laser; at the same time, the femtosecond laser can also be used for etching using line scanning direct writing or multi-focus parallel processing to obtain a transfer mold with a multi-level microstructure, which will not be repeated here.

[0037] S20, replicating the multi-level microstructure on the upper surface of the transfer mold onto the upper surface of the flexible substrate by compression molding to obtain a flexible multi-level substrate, wherein the flexible multi-level substrate has a multi-level microstructure; Specifically, the multi-level microstructure on the upper surface of the transfer mold can be replicated to the upper surface of the flexible substrate by compression molding, or the flexible multi-level substrate can be prepared in batches by compression molding through other methods such as injection molding and nanoimprinting. The flexible multi-level substrate described in this application can be made of silicone material, or one of other flexible and elastic materials such as polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyimide (PI), polypropylene (PP), polycarbonate (PC), polyurethane (PU), epoxy resin (ER), polydimethylsiloxane (PDMS), etc. Silicone material has synergistic matching advantages in density, tensile properties, skin-friendliness, environmental tolerance and adhesion to conductive materials, and is suitable as a flexible sensor substrate material; in addition, silicone softens at higher temperatures, making it easy to achieve a precise replication process of compression molding. Silicone's lightweight properties meet the requirements of portable devices, and its ultra-wide operating temperature range ensures the stability of extreme sensors in extreme environments. Furthermore, silicone's low elastic modulus gives the substrate a highly sensitive response to deformation, while its ultra-high elongation at break ensures the device's structural reliability under dynamic deformation. These properties are highly consistent with the sensor's requirements for mechanical compatibility, environmental tolerance, and signal fidelity of the substrate material. Therefore, in this case, high-temperature vulcanized silicone rubber, or silicone, was selected as the sensor substrate material. Using the precision mold obtained in the previous step and precision compression molding, silicone substrates containing multi-layered microstructures can be mass-produced.

[0038] Further, see Figure 2 The multi-level microstructure on the upper surface of the transfer mold is copied to the upper surface of the flexible substrate by compression molding to obtain a flexible multi-level substrate, wherein the flexible multi-level substrate has a multi-level microstructure, including: S21. Provide a compression molding device, the compression molding device comprising a punch and a retaining structure, the punch having a cavity for accommodating the transfer mold; the punch being movable in a vertical direction; the retaining structure having a cavity for accommodating the flexible substrate, the cavity of the retaining structure for accommodating the flexible substrate being arranged opposite to the cavity of the punch for accommodating the transfer mold; S22, fixing the flexible substrate in the cavity of the holding structure; S23. Control the punch and the transfer mold to move downward so as to press the flexible substrate against the punch and deform it, thereby forming the flexible substrate to obtain a flexible multi-level substrate 1 with a multi-level microstructure on the upper surface; the microporous structure on the upper surface of the transfer mold is transferred into the micropillars 2 on the upper surface of the flexible multi-level substrate 1, and the trapezoidal groove structure on the upper surface of the transfer mold is transferred into the reinforcing ribs 3 on the upper surface of the flexible multi-level substrate 1; and irregular micro-nano structures are transferred onto the surfaces of the micropillars 2 and the reinforcing ribs 3.

[0039] Specifically, compression molding is performed by using a transfer mold. When the micropillars 2 and the reinforcing ribs 3 are transferred to the upper surface of the flexible multi-level substrate, the irregular micro-nanostructure induced by the femtosecond laser on the mold surface is also transferred to the flexible multi-level substrate, so that the micropillars 2 and the reinforcing ribs 3 of the flexible multi-level substrate after the transfer are provided with irregular micro-nanostructures, thereby forming a multi-level microstructure for improving the sensitivity of pressure detection. Femtosecond laser processing is widely used in microstructure processing due to its advantages such as high processing precision, wide material adaptability, simple process flow, and no tool wear. However, for industrial-grade mass production, such as directly using femtosecond laser processing to produce a flexible sensor substrate, the processing cycle is relatively long, and the processing of 12×12mm 2 The micro-nano structure of a certain area takes 90 minutes, which is difficult to meet the demand for low-cost batch preparation; while the conventional precision compression molding method takes about 7 minutes to copy the mold surface structure to the silicone surface, which greatly reduces the processing cycle of the micro-nano structure. The compression molding device is a single-station device, and the molding temperature of the compression molding device is 170°C, the molding pressure is 500N, and the molding time is 400s. Multi-station compression molding equipment can also be used in the present invention, and the production time of the silicone matrix can be shortened to about 60s, greatly improving production efficiency. The working process of the multi-station compression molding equipment is a prior art and will not be repeated here.

[0040] See also Figure 4 、 Figure 5 and Figure 6 , wherein the flexible multi-level substrate 1 having a multi-level microstructure is as follows under a microscope Figure 6 As shown in a in FIG, the multi-level microstructure obtained by replication on the upper surface of the flexible multi-level substrate 1 is as shown in FIG. Figure 6 As shown in b, the multi-level microstructure includes a first microstructure layer, a second microstructure layer and a third microstructure layer. The first microstructure layer is an array of micropillars 2 arranged in a square array, as shown in FIG. Figure 6 As shown in Figure c, each microcolumn 2 is in the shape of a regular quadrangular pyramid with a height of 100 μm and an upper surface size of 80×80 μm. 2 , the lower surface size is 100×100μm 2, with a spacing of 300μm; the micropillars 2 improve the compressibility of the flexible pressure sensor structure, reduce the internal structural hardening, make the stress distribution more uniform, and help achieve linear deformation. The second microstructure layer is a reinforcing rib 3, the two ends of which are respectively connected to the micropillars 2 in different rows or columns, and the micropillars 2 are located at the intersection of the reinforcing ribs 3, such as Figure 6 As shown in d, the cross section of the reinforcement rib 3 is a trapezoid, with an upper side length of 50 μm, a lower side length of 60 μm, and a height of 20 μm; the total area of ​​the mold surface microstructure array is 12×12 mm 2 The reinforcing ribs 3 include mutually parallel transverse reinforcing ribs and mutually parallel longitudinal reinforcing ribs. The transverse and vertical reinforcing ribs are perpendicular to each other. The height of the reinforcing ribs 3 is slightly lower than the micropillars 2, providing support. Furthermore, the intersecting transverse and longitudinal reinforcing ribs form accommodation spaces, further increasing the contact area. The third microstructure layer comprises irregular micro-nanostructures disposed on the surfaces of the micropillar array 2 and the reinforcing ribs 3. These irregular micro-nanostructures are generated by femtosecond laser induction. When the upper surface of the first conductive flexible substrate and the upper surface of the second conductive flexible substrate are in contact, the micropillars 2 on the upper surface of the first conductive flexible substrate are located in the accommodation spaces between the reinforcing ribs 3 of the second conductive flexible substrate, and the micropillars 2 on the upper surface of the second conductive flexible substrate are located in the accommodation spaces between the reinforcing ribs 3 of the first conductive flexible substrate. The present invention utilizes a novel combined method of femtosecond laser processing and compression molding to fabricate flexible sensors, leveraging the advantages of both processes to achieve industrial processing of flexible sensors with multi-level microstructures. Figure 5 The "e" in the figure represents the irregular micro-nanostructure produced by laser induction and etching on the transfer mold. The irregular micro-nanostructure is a micro-nanocomposite structure. Since the height of the micropillars 2 is greater than the reinforcing ribs 3, the multi-level microstructure formed by the micropillars 2 and the reinforcing ribs 3 can meet the requirements of enhancing the sensitivity of the multi-level microstructure. On the other hand, the surfaces of the micropillars 2 and the reinforcing ribs 3 on the flexible multi-level substrate 1 obtained by transfer have irregular micro-nanostructures, further increasing the contact area of ​​the interlocking structure and improving the sensitivity. At the same time, Figure 5 The f in the figure represents the multi-level microstructure after 100 times of the compression molding process. It can be seen that the transfer mold obtained by femtosecond laser etching in this application has a low degree of wear and can maintain a strong consistency between different batches of flexible multi-level substrates 1, meeting the processing efficiency, structural consistency and replication accuracy requirements of the multi-level microstructure for batch processing of flexible sensors.

[0041] S30, preparing a conductive material layer on the upper surface of the flexible multi-level substrate 1 to obtain a first conductive flexible substrate 11 and a second conductive flexible substrate 12, wherein the upper surface of the first conductive flexible substrate 11 has a first conductive material layer, and the upper surface of the second conductive flexible substrate 12 has a second conductive material layer; Please refer to Figures 1 to 4 For example, the present application uses a spray gun to evenly spray a layer of conductive material on the surface of a flexible multi-level substrate 1 containing a multi-level microstructure to prepare a conductive material layer, so that the flexible multi-level substrate 1 has better conductivity, thereby obtaining a conductive flexible substrate. The conductive material layer is an important structure of the piezoresistive flexible sensor. The conductive material can be selected from one of graphene, conductive carbon black, conductive polymer, graphite sheet, metal nanoparticles, and Mxenes materials. Preferably, the conductive material layer is graphene. The structure of the first conductive flexible substrate 11 and the second conductive flexible substrate 12 is as shown in FIG. Figure 3 As shown in the conductive flexible substrate in FIG, the first conductive flexible substrate 11 and the second conductive flexible substrate 12 have the same size and the same structure.

[0042] The reinforcing ribs 3 serve to increase the upper surface area of ​​the conductive flexible substrate. When the sensor is subjected to gradually increasing pressure, the reinforcing ribs 3 and micro-pillars 2 inside it are deformed by stress or pressure, and the contact points of the reinforcing ribs 3 change. The flexible sensor detects the stress or pressure changes on its surface by increasing the changes in the contact points. By increasing the upper surface area of ​​the conductive flexible substrate, the amplitude of the change in the contact points when the stress changes is increased, thereby increasing the sensitivity and detection range of the sensor. At the same time, the reinforcing ribs 3 serve to assist in supporting the micro-pillars 2, enabling the sensor to withstand a larger load limit and further increasing the detection range of the sensor. The reinforcing ribs 3 structure and the micro-pillars 2 are located on the upper surface of the conductive flexible substrate. Figure 4 The present invention is shown Figure 3 In the cross-sectional schematic diagram along the arrow direction, for ease of explanation, the upper surface of the conductive flexible substrate at the lowest height is defined as the first upper surface, the upper surface of the micropillar 2 is defined as the second upper surface, and the upper surface of the reinforcing rib 3 structure is defined as the third upper surface. It should be noted that the reinforcing rib 3 structure and micropillar 2 on the conductive flexible substrate can be flattened and extended according to actual production needs. Only the multi-level microstructure etched on the transfer mold needs to be adaptively designed. This application will not be repeated here. The first conductive flexible substrate 11 and the second conductive flexible substrate 12 can be square, or any polygonal shape such as rectangle, circle, triangle, or a custom shape. By trimming and removing the edges and redundant conductive flexible substrates, flexible sensors of different shapes and sizes can be obtained, which can be flexibly and conveniently attached to surfaces of different morphologies.

[0043] S40 , overlapping the upper surface of the first conductive flexible substrate 11 and the upper surface of the second conductive flexible substrate 12 to form an interlocking structure.

[0044] Specifically, the present application arranges the upper surfaces of the first conductive flexible substrate 11 and the second conductive flexible substrate 12 with multi-level microstructures to overlap with each other, ensures that the multi-level microstructure of the first conductive flexible substrate 11 is interlocked with the multi-level microstructure of the second conductive flexible substrate 12, and seals them to avoid the influence of the external environment on the sensor performance, thereby completing the packaging of the flexible sensor.

[0045] Furthermore, the upper surface of the first conductive flexible substrate 11 and the upper surface of the second conductive flexible substrate 12 are superimposed to form an interlocking structure, and encapsulated to obtain the flexible pressure sensor, including: S41. Weld and fix a wire to the upper surface of the first conductive flexible substrate 11 or the second conductive flexible substrate 12; the wire is made of conductive metal, and is respectively connected to the upper surface of the first conductive flexible substrate 11 and the upper surface of the second conductive flexible substrate 12, and the other end is connected to conduct the internal resistance change when the flexible sensor is deformed. The conductive metal is preferably a copper wire.

[0046] S42, placing the upper surfaces of the first conductive flexible substrate 11 and the second conductive flexible substrate 12 opposite to each other, so that an interlocking structure is formed between the first conductive flexible substrate 11 and the second conductive flexible substrate 12; Specifically, the top surfaces of the first and second conductive flexible substrates 11, 12, having multi-level microstructures, are stacked relative to each other, ensuring that the micropillars 2 of the second conductive flexible substrate 12 are located within the spaces formed by the transverse and longitudinal reinforcing ribs on the first conductive flexible substrate 11. The micropillars 2 of the first conductive flexible substrate 11 are located within the spaces formed by the intersecting reinforcing ribs 3 on the second conductive flexible substrate 12. The micropillars 2 of the first conductive flexible substrate 11 abut against the lower surface of the recessed portion of the second conductive flexible substrate 12, which is surrounded and isolated by the reinforcing ribs 3, forming an interlocking structure.

[0047] S50 , performing a sealing process on the stacked first conductive flexible substrate and the second conductive flexible substrate to obtain the flexible pressure sensor.

[0048] Specifically, the stacked first conductive flexible substrate 11 and second conductive flexible substrate 12 are sealed. Specifically, medical tape or tape made of other materials can be used for sealing, or a hot-melt sealant can be used to seal the frame, thereby encapsulating the flexible sensor and obtaining a flexible sensor with good sealing performance. This can isolate the sensor from the effects of the external environment on its performance, thereby improving reliability.

[0049] The process flow chart of combined femtosecond laser processing and compression molding is as follows: Figure 2 As shown in Figure 2, the process design of the flexible pressure sensor is divided into multiple steps, ranging from the preparation of a flexible substrate with a multi-layer structure to the final sensor packaging. First, a femtosecond laser is used to etch a microstructure array on the surface of a titanium alloy substrate to prepare a titanium alloy mold. The surface morphology of the mold under a microscope is shown in Figure 2. Figure 5 As shown. Among them, Figure 5 a in the figure represents the surface morphology of the transfer mold prepared by the method for preparing a flexible pressure sensor of the present invention under a microscope; Figure 5 b in the figure represents the surface morphology of the multi-level microstructure array on the upper surface of the transfer mold under a microscope; Figure 5 The c in the figure represents the surface morphology of the microporous structure under a microscope; Figure 5 The d in the figure represents the surface morphology of the trapezoidal groove structure under a microscope; Figure 5 Figure e shows the surface morphology of the multi-level microstructure on the transfer mold after laser induction and etching under a microscope; Figure 5 Figure f shows the surface morphology of the multi-level microstructure under a microscope after 100 compression molding processes.

[0050] Specifically, the multi-level microstructure array on the transfer mold surface is copied to the silicone surface by a compression molding process to prepare a flexible multi-level substrate containing multi-level microstructures. The substrate morphology is as follows: Figure 6 shown; among them, Figure 6 a in the figure represents the surface morphology of the flexible multi-level substrate prepared by the method for preparing the flexible pressure sensor of the present invention under a microscope; Figure 6 b in the figure shows the surface morphology of the multi-level microstructure obtained by replication on the upper surface of the flexible multi-level substrate under a microscope; Figure 6 Figure c shows the surface morphology of micropillar 2 under a microscope; Figure 6 The d in the figure represents the surface morphology of the reinforcing rib 3 under a microscope. Due to the use of compression molding, the multi-level microstructure on the upper surface of the flexible multi-level substrate corresponds to the multi-level microstructure on the transfer mold, that is, the microporous structure on the transfer mold corresponds to the micropillars 2 on the flexible multi-level substrate after transfer, and the trapezoidal groove structure on the transfer mold corresponds to the reinforcing rib 3 on the flexible multi-level substrate after transfer. Then, graphene is sprayed onto the conductive flexible substrate to make the substrate conductive. Take two conductive flexible substrates of the same size and structure prepared by the above method, combine them together in the direction of relative superposition of the microstructures to form an interlocking structure; the superimposed first conductive flexible substrate and the second conductive flexible substrate are sealed to obtain the flexible pressure sensor.

[0051] The present invention combines the advantages of high-precision processing of femtosecond lasers and mass production of compression molding technology to propose a new preparation method. First, a femtosecond laser is used to prepare a multi-level microstructure on a mold substrate. Then, compression molding technology is used to replicate the above microstructure onto the surface of flexible silicone, thereby obtaining a flexible substrate with a multi-level microstructure. Then, the above flexible substrate is encapsulated to prepare a high-performance flexible piezoresistive sensor. The synergistic advantages of this combined method are specifically manifested in that femtosecond laser processing can ensure high precision and good consistency of the prepared microstructure, while compression molding technology can achieve low-cost mass production of flexible substrates with microstructures. At the same time, the developed flexible piezoresistive sensor uses the above flexible substrate film sprayed with double-layer graphene as the core component, supplemented by conductive circuits and packaging protective layers, to form a complete sensing system with an interlocking structure, achieving the unity of high sensitivity, high linearity and wide sensing range of the device, meeting the performance indicators of high sensitivity and wide detection range.

[0052] Second, please also refer to Figure 7 In some preferred embodiments of the present invention, a flexible pressure sensor is further provided, which is obtained by the above-mentioned method for preparing a flexible pressure sensor; the flexible pressure sensor includes: a first conductive flexible substrate 11, a first conductive material layer, a second conductive flexible substrate 12, a second conductive material layer and a metal wire; wherein the upper surface of the first conductive flexible substrate 11 and the upper surface of the second conductive flexible substrate 12 respectively have a multi-level microstructure, the upper surface of the first conductive flexible substrate 11 and the upper surface of the second conductive flexible substrate 12 are in contact with each other, the first conductive material layer (not shown in the figure) is located on the upper surface of the first conductive flexible substrate 11, and the second conductive material layer (not shown in the figure) is located on the upper surface of the second conductive flexible substrate 12.

[0053] Specifically, the flexible pressure sensor comprises a first conductive flexible substrate 11, a first conductive material layer, a second conductive flexible substrate 12, a second conductive material layer, and a metal wire. The first conductive material layer is obtained by spraying a conductive material onto the upper surface of the first conductive flexible substrate 11 and then drying and curing it. The second conductive material layer is obtained by spraying a conductive material onto the upper surface of the second conductive flexible substrate 12 and then drying and curing it. The first conductive material layer and the second conductive material layer are in contact with each other, and the metal wire is connected to either the first conductive material layer or the second conductive material layer. When the flexible pressure sensor receives pressure, the multi-level microstructures on the upper surfaces of the first conductive flexible substrate 11 and the second conductive flexible substrate 12 are subjected to force, causing their internal resistance to change.

[0054] Furthermore, the multi-level microstructure is divided into two layers, the first layer is an array of micropillars 2 arranged in a square array, each micropillar 2 is in the shape of a regular quadrangular pyramid, and the second layer is a reinforcing rib 3, the cross-section of the reinforcing rib 3 is a trapezoid; the two ends of the reinforcing rib 3 are respectively connected to the micropillars 2, and the micropillars 2 are located at the intersection of the reinforcing ribs 3; when the upper surface of the first conductive flexible substrate 11 and the upper surface of the second conductive flexible substrate 12 are abutted, the micropillars 2 on the upper surface of the first conductive flexible substrate 11 are located in the accommodation space between the reinforcing ribs 3 of the second conductive flexible substrate 12, and the micropillars 2 on the upper surface of the second conductive flexible substrate 12 are located in the accommodation space between the reinforcing ribs 3 of the first conductive flexible substrate 11, thereby forming an interlocking structure. The microcolumns 2 have a height of 100 μm, an upper surface size of 80×80 μm2, a lower surface size of 100×100 μm2, and a spacing of 300 μm; the upper side length, lower side length, and height of the reinforcing ribs 3 are 50 μm, 60 μm, and 20 μm, respectively.

[0055] For details, please refer to Figure 8 , Figure 8 Figure a shows a schematic diagram of the flexible pressure sensor in a flat state. Figure 8 b in the figure is a schematic diagram of the state of the flexible pressure sensor under stress and bending. It can be seen that the flexible sensor in this application has dynamic deformation capabilities and meets the needs of portable devices. This application systematically tests the sensitivity, pressure detection range, response time and other performance of the flexible sensor. The sensor prepared based on the above method shows significant performance advantages: specifically, its total detection range is 0-420kPa, which is much larger than that of conventional flexible piezoresistive sensors; and the cyclic stability of the flexible sensor in this application exceeds 5000 times, the lowest detection pressure value is 14Pa, and the sensitivity of the flexible sensor reaches -0.19793kPa at 0-2.3kPa. -1 , which falls into the high sensitivity category. Furthermore, dynamic testing shows that the flexible sensor in this application has a loading response time of 40ms and a recovery response time of 60ms, demonstrating sub-second response characteristics. Furthermore, application verification demonstrates that the flexible sensor fabricated using the flexible sensor fabrication method described in this application can accurately capture the characteristics of human pulse waveforms, vocal cord vibration spectra, and the mechanical characteristics of grasping movements.

[0056] In summary, the present invention discloses a method for preparing a flexible pressure sensor and a flexible pressure sensor. The method comprises: etching a multi-level microstructure on the upper surface of a mold substrate using a femtosecond laser to obtain a transfer mold; replicating the multi-level microstructure on the upper surface of the transfer mold to the upper surface of a flexible substrate by compression molding to obtain a flexible multi-level substrate, wherein the flexible multi-level substrate has a multi-level microstructure; preparing a conductive material layer on the upper surface of the flexible multi-level substrate to obtain a flexible substrate having a conductive layer; and superimposing the upper surfaces of the two conductive flexible substrates relative to each other, with the microstructures staggered and in contact to form an interlocking structure, and encapsulating the flexible pressure sensor. The method has the following beneficial effects: A transfer mold with a multi-level microstructure is obtained through femtosecond laser processing, and the multi-level microstructure is replicated by precision molding of the transfer mold, which simplifies the processing procedure of the multi-level microstructure flexible sensor, improves the precision processing efficiency of flexible sensors with complex or composite structures, and realizes low-cost batch preparation of flexible substrates with microstructures.

[0057] By obtaining a transfer mold through femtosecond laser processing and precision molding the transfer mold, the flexible sensor with a multi-layer microstructure prepared shows significant performance advantages and meets the category of high-performance flexible sensors.

[0058] The composite method of laser processing and compression molding is adopted to ensure the morphological accuracy of the microstructure and the consistency of the array, realize the mass production of flexible multi-level microstructure matrix, greatly reduce the preparation cost of the flexible matrix, and facilitate the large-scale production of flexible sensors.

[0059] It should be understood that the application of the present invention is not limited to the above examples. For those skilled in the art, improvements or changes can be made based on the above description. All these improvements and changes should fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for preparing a flexible pressure sensor, characterized in that: include: A femtosecond laser is used to etch a multi-level microstructure on the upper surface of the mold substrate to obtain a transfer mold; replicating the multi-level microstructure on the upper surface of the transfer mold onto the upper surface of the flexible substrate by compression molding to obtain a flexible multi-level substrate having a multi-level microstructure; Preparing a conductive material layer on the upper surface of the flexible multi-level substrate to obtain a first conductive flexible substrate and a second conductive flexible substrate, wherein the upper surface of the first conductive flexible substrate has a first conductive material layer, and the upper surface of the second conductive flexible substrate has a second conductive material layer; overlapping the upper surface of the first conductive flexible substrate and the upper surface of the second conductive flexible substrate to form an interlocking structure; The first conductive flexible substrate and the second conductive flexible substrate that are stacked are sealed to obtain the flexible pressure sensor.

2. The method for preparing a flexible pressure sensor according to claim 1, wherein: The method of etching a multi-level microstructure on the upper surface of the mold substrate using a femtosecond laser to obtain a transfer mold includes: A femtosecond laser is used to etch a microporous structure array on the upper surface of the transfer mold, wherein the microporous structure array is arranged in a square array; A femtosecond laser is used to etch a trapezoidal groove structure on the upper surface of the transfer mold, wherein the two ends of the trapezoidal groove structure are respectively connected to the micropore structures in adjacent rows or connected columns, and the micropore structure is located at the intersection of the trapezoidal groove structures; the surfaces of the micropores and the trapezoidal groove structure have irregular micro-nano structures after femtosecond laser induction.

3. The method for preparing the flexible pressure sensor according to claim 2, wherein: The multi-level microstructure on the upper surface of the transfer mold is copied to the upper surface of the flexible substrate by compression molding to obtain a flexible multi-level substrate having a multi-level microstructure, including: A compression molding device is provided, comprising a punch and a holding structure, wherein the punch has a cavity for accommodating the transfer mold; the punch is movable in a vertical direction; the holding structure has a cavity for accommodating the flexible substrate, and the cavity of the holding structure for accommodating the flexible substrate is arranged opposite to the cavity of the punch for accommodating the transfer mold; securing the flexible substrate within the cavity of the retaining structure; The punch and the transfer mold are controlled to move downward so as to press the flexible substrate against the punch and deform it, thereby forming the flexible substrate to obtain a flexible multi-level substrate with a multi-level microstructure on the upper surface; the microporous structure on the upper surface of the transfer mold is transferred into micropillars on the upper surface of the flexible multi-level substrate, and the trapezoidal groove structure on the upper surface of the transfer mold is transferred into reinforcing ribs on the upper surface of the flexible multi-level substrate; irregular micro-nano structures are transferred on the surfaces of the micropillars and the reinforcing ribs.

4. The method for preparing a flexible pressure sensor according to claim 1, wherein: The upper surface of the first conductive flexible substrate and the upper surface of the second conductive flexible substrate are overlapped to form an interlocking structure, and encapsulated to obtain the flexible pressure sensor, comprising: Welding and fixing the wire on the upper surface of the first conductive flexible substrate or the second conductive flexible substrate; placing upper surfaces of a first conductive flexible substrate and a second conductive flexible substrate facing each other, forming an interlocking structure between the first conductive flexible substrate and the second conductive flexible substrate; The stacked first conductive flexible substrate and the second conductive flexible substrate are sealed.

5. The method for preparing the flexible pressure sensor according to claim 3, wherein: The compression molding device is a single-station device, the compression molding temperature of the compression molding device is 170° C., the compression pressure is 500 N, and the total compression time is 400 s.

6. The method for preparing a flexible pressure sensor according to claim 2, wherein: The microporous structure is in the shape of a regular quadrangular prism, the depth of the microporous structure is 100 μm, and the top surface size is 100×100 μm. 2 , the bottom surface size is 80×80μm 2 The spacing between each micropore is 300μm; the cross-section of the trapezoidal groove structure is a regular trapezoid, the depth of the trapezoidal groove structure is less than the depth of the micropore structure, the upper side length of the trapezoidal groove structure is 60μm, and the lower side length is 50μm.

7. The method for preparing a flexible pressure sensor according to claim 2, wherein: The transfer mold adopts a titanium alloy substrate, and the titanium alloy substrate adopts a TC4 titanium alloy element ratio.

8. A flexible pressure sensor, characterized in that: The flexible pressure sensor is obtained by the preparation method of the flexible pressure sensor according to any one of claims 1 to 7; the flexible pressure sensor includes: a first conductive flexible substrate, a first conductive material layer, a second conductive flexible substrate, a second conductive material layer and a metal wire; wherein, the upper surface of the first conductive flexible substrate and the upper surface of the second conductive flexible substrate respectively have a multi-level microstructure, the upper surface of the first conductive flexible substrate and the upper surface of the second conductive flexible substrate are abutted, the first conductive material layer is located on the upper surface of the first conductive flexible substrate, and the second conductive material layer is located on the upper surface of the second conductive flexible substrate.

9. The flexible pressure sensor according to claim 8, characterized in that: The multi-level microstructure includes a first microstructure layer, a second microstructure layer and a third microstructure layer. The first microstructure layer is micropillars arranged in a square array, the second microstructure layer is a reinforcing rib, the two ends of the reinforcing rib are respectively connected to the micropillars, and the micropillars are located at the intersection of the reinforcing ribs; the third microstructure layer is an irregular micro-nano structure arranged on the surface of the micropillars and the reinforcing ribs; when the upper surface of the first conductive flexible substrate and the upper surface of the second conductive flexible substrate are in contact with each other, the micropillars on the upper surface of the first conductive flexible substrate are located in the accommodation space between the reinforcing ribs of the second conductive flexible substrate, and the micropillars on the upper surface of the second conductive flexible substrate are located in the accommodation space between the reinforcing ribs of the first conductive flexible substrate.

10. The flexible pressure sensor according to claim 9, characterized in that: The microcolumns are in the shape of regular quadrangular pyramids, and the cross section of the reinforcing ribs is trapezoidal.

Images