Multilayer stress sensor prepared based on laser direct writing technology and preparation method thereof

Abstract

The invention discloses a multilayer stress sensor prepared based on a laser direct writing technology and a preparation method thereof, and belongs to the technical field of flexible electronic device preparation. The sensor is in a Y shape, three sensors extend from the center point along three different angles, and the center points of the three sensors are connected with one another. The invention discloses a multilayer stress sensor prepared based on a laser direct writing technology. The multilayer stress sensor is prepared on a doped flexible substrate by adopting the laser direct writing technology. Through a laser direct writing technology based on flexible substrate doping, a strain sensor unit capable of realizing plane strain direction identification is prepared. Finite element simulation and mechanical test prove that the sensing unit has the capability of realizing strain direction identification on a plane. The multilayer stress sensor prepared based on the laser direct writing technology and the preparation method thereof can realize preparation of a large-scale sensing unit array compatible with a complex three-dimensional curved surface; the method has a wide application prospect in the fields of aerospace, building structure health monitoring and the like.

Description

Technical Field

[0001] This invention relates to the field of flexible electronic device fabrication technology, and more specifically, to a multilayer stress sensor based on laser direct writing technology and its fabrication method. Background Technology

[0002] Flexible electronics is a transformative technology that has emerged in recent years. It involves depositing electronic materials and devices onto flexible substrates, thereby endowing them with properties such as bendability, foldability, and stretchability that are not found in traditional electronic materials and devices. In recent years, with the research of new materials and processes, this field has seen vigorous development in academic and industrial communities both domestically and internationally.

[0003] Strain sensing units capable of identifying strain direction are crucial in key areas such as humanoid robots with artificial skin, structural health monitoring of buildings, and flexible skin for aircraft. For example, identifying strain direction is one of the important functions of human skin. Artificial humanoid electronic skin, composed of multiple sensing units with strain direction identification capabilities, can meet the requirements for strain direction identification.

[0004] However, current strain sensing units face numerous challenges in terms of integration density, manufacturing cost, complexity of large-scale manufacturing, and sensor patterning. These problems are particularly prominent in practical applications, as many surfaces to be monitored are typically three-dimensional and uneven. This necessitates that the fabrication process of the sensing unit transcend two-dimensional planes and be compatible with three-dimensional surfaces. These issues have significantly limited the development of strain sensors. Therefore, researching a strain sensing unit that can achieve large-scale, high-density manufacturing and controllable patterning at low cost, while also being compatible with three-dimensional surfaces, is of great significance for the practical application of strain sensors. Summary of the Invention

[0005] Based on the aforementioned problems in the existing technology, the purpose of this application is to provide a multilayer stress sensor and its fabrication method based on laser direct writing technology. By integrating the sensing unit through flexible substrate doping and laser direct writing technology, the integration density of the sensor array can be improved, and the fabrication cost is low. It is easy to fabricate on a large scale and patterned design, while the overall process is compatible with the fabrication of three-dimensional curved surfaces with arbitrary shapes.

[0006] The technical solution adopted by this application to solve its technical problem is: a multilayer stress sensor based on laser direct writing technology, including a multilayer stress sensor, wherein the multilayer stress sensor has two conductive layers, namely an upper layer and a lower layer. The substrate of the lower layer is composed of a mixed colloid composed of a flexible polymer, conductive nanomaterials and a catalyst; the upper layer is a metal conductive layer formed by laser catalytic chemical plating and closely connected to the lower layer.

[0007] Furthermore, the multilayer stress sensor is Y-shaped, with three sensors extending from the center point at three different angles, and the center points of the three sensors are connected to each other.

[0008] Furthermore, the multilayer stress sensor is fabricated on a doped flexible substrate using laser direct writing technology.

[0009] Furthermore, the angles between the three sensors and the size of the sensors can be adjusted by controlling the laser etching method using a pre-drawn laser control file.

[0010] Furthermore, when the sensor generates strain on a two-dimensional plane, the resistance change trends of the three sensors within the sensing unit are significantly correlated with the strain angle and amplitude.

[0011] Furthermore, the flexible polymer includes polymers such as polydimethylsiloxane and styrene polymers that can serve as doping support substrates.

[0012] Furthermore, the conductive nanomaterials include conductive nanomaterials such as carbon nanotubes and carbon black.

[0013] Furthermore, the catalyst includes materials such as ATO that catalyze the acceleration of the electroless plating process.

[0014] A method for fabricating a multilayer stress sensor based on laser direct writing technology includes the following fabrication steps: S1: Mix the flexible polymer with conductive nanomaterials and photoactivated catalyst in a certain proportion and stir thoroughly to make the dopant evenly distributed in the substrate, forming a conductive flexible polymer colloid doped with photoactivated catalyst; then add an appropriate amount of curing agent, and continue stirring under vacuum until no bubbles are generated. S2: Spray silicone release agent onto the glass slide, heat and dry it on the drying rack, then spin coat the prepared conductive polymer colloid onto the glass slide on a high-speed centrifugal spin coater to form a uniformly distributed colloid, and then place it on the drying rack to heat and cure it to form a film of uniform thickness.

[0015] S3: Treat the conductive film with a laser of appropriate power as required, and then clean the film surface with water.

[0016] S4: Prepare the chemical plating solution according to the specified ratio and stir thoroughly. Place the laser-treated film into the solution, seal it, and place it in a constant temperature chamber for chemical plating.

[0017] S5: Take out the thin film, wash it with clean water and dry it. Peel the thin film off the glass plate to obtain the required sensor and complete the preparation of the strain sensing unit.

[0018] Further, in step S1, the weight ratio of conductive carbon nanotubes to flexible polymer PDMS is 1%-6%, the weight ratio of photoactivated catalyst ATO to flexible polymer PDMS is 3%-6%, and the weight ratio of curing agent to PDMS is 1:10-1:5; in step S2, the drying of the silicone release agent is carried out by heating on a 150°C baking rack for 10 minutes, and the spin coating step is carried out on a high-speed centrifugal spin coater at a speed of 400 r / min for 2 minutes. During the heating and curing process, the baking rack temperature is set to 150°C and the heating time is 5 minutes; in step S3, the laser treatment involves using an ultraviolet laser at a laser frequency of 20-60 kHz and a speed of 2000 mm / s to perform laser-activated etching on multiple "Y"-shaped regions, followed by laser etching at 20 kHz and 10 kHz. The edge of the area is cut at a speed of mm / s; in step 4, the chemical plating solution is prepared by water, copper plating solution component A and copper plating solution component B in a mass ratio of 15:2:1, the temperature of the constant temperature chamber is set to 30°C, the humidity is 20%, and the chemical plating time is 4 hours.

[0019] The beneficial effects of this invention are as follows: This invention provides a design method for a strain sensor unit with strain direction recognition function based on laser direct writing technology. Compared with the traditional discrete sensor layout, the integrated sensing unit can effectively improve the integration density of sensing units in the array and achieve higher precision strain monitoring. This fabrication scheme has the characteristics of low cost, ease of large-scale manufacturing and patterning, and compatibility with three-dimensional surface fabrication. Attached Figure Description

[0020] The accompanying drawings, which form part of this specification, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A CAD image showing the dimensions of a typical strain sensing unit. Figure 2 The fabrication and packaging process of the strain sensing unit; Figure 3 Optical images and angle divisions of the fabricated and packaged sensing unit; Figure 4 Finite element simulation of strain generated within the sensing unit when stretched at different angles; Figure 5 Finite element simulation of strain distribution within the sensing unit when stretched at different angles; Figure 6 The strain amplitude of different sensors in the sensing unit under different angular strains after fitting; Figure 7The resistance change of the sensor device is measured at a fixed strain angle of 45°, within three cycles of 0% to 32% strain increments of 4%. Figure 8 A flexible aircraft skin was prepared by brushing a doped conductive colloid onto the surface of a scaled-down aircraft model and then heating and curing it. Figure 9 Optical image of a flexible aircraft skin fabricated on a model surface after laser etching; Figure 10 Aircraft skin and sensor array for wind pressure monitoring fabricated on the surface of a scaled-down aircraft model. Detailed Implementation

[0021] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0022] It should be noted that, unless otherwise specified, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0023] In this invention, unless otherwise stated, the directional terms such as "up" and "down" generally refer to the directions shown in the accompanying drawings, or to the vertical, perpendicular, or gravitational direction; similarly, for ease of understanding and description, "left" and "right" generally refer to the left and right shown in the accompanying drawings; "inner" and "outer" refer to the inner and outer contours of each component itself, but the above directional terms are not intended to limit this invention.

[0024] A multilayer stress sensor fabricated using laser direct writing technology includes two conductive layers, an upper layer and a lower layer. The substrate of the lower layer is composed of a mixed colloid consisting of a flexible polymer, conductive nanomaterials, and a catalyst; the upper layer is a tightly bonded metallic conductive layer formed by laser-catalyzed electroless plating. This multilayer stress sensor, fabricated using laser direct writing technology, is shaped like a "Y". It consists of three sensors extending from a central point at three different angles, with the central points of the three sensors connected to each other.

[0025] This multilayer stress sensor, fabricated using laser direct writing technology, utilizes a flexible substrate doping process and laser direct writing. On a flexible substrate doped with nano-conductive materials and a catalyst, copper is selectively grown using laser direct writing to fabricate strain sensing units with characteristic shapes capable of monitoring strain direction. This method is applicable to the fabrication of stress sensing unit arrays on arbitrary three-dimensional curved surfaces.

[0026] Flexible substrate doping process: The flexible substrate is mixed with a certain proportion of nano-conductive materials and catalysts, stirred and then heated to solidify.

[0027] Laser direct writing technology is a process that uses lasers to process flexible substrates doped with catalysts such as ATO, and then immerses the thin film in a chemical plating solution to grow a metal-sensitive thin film. Its core is to control the selective growth of the metal layer by controlling parameters such as the pattern, power, and speed of the laser processing, thereby enabling the fabrication of sensors of arbitrary size and pattern.

[0028] A Y-shaped sensor composed of three sensors can simultaneously provide strain information in three directions when stretched in a plane, thereby enabling the identification of plane strain angle and orientation.

[0029] The angles between the three sensors and the size of the sensing units can be adjusted by controlling the laser etching method through a pre-drawn laser control file.

[0030] When a multilayer stress sensor based on laser direct writing technology is strained on a two-dimensional plane, the resistance change trend of the three sensors in the sensing unit is significantly correlated with the strain angle and amplitude.

[0031] This multilayer stress sensor, fabricated using laser direct writing technology, comprises two conductive layers, an upper layer and a lower layer. The substrate of the lower layer is composed of a mixed colloid consisting of a flexible polymer, conductive nanomaterials, and a catalyst; the upper layer is a tightly bonded metallic conductive layer formed by laser-catalyzed electroless plating.

[0032] Flexible polymers include polymers such as polydimethylsiloxane and styrene polymers that can be used as doping support substrates.

[0033] Conductive nanomaterials include conductive nanomaterials such as carbon nanotubes and carbon black.

[0034] Catalysts include materials such as ATO that can catalyze and accelerate the electroless plating process.

[0035] A method for fabricating a multilayer stress sensor based on laser direct writing technology includes the following fabrication steps: S1.1: Mix PDMS and ATO in a weight ratio of 100:5 and stir thoroughly to ensure that the dopant is evenly distributed in the substrate to form a flexible polymer colloid doped with a photoactivated catalyst. Then add a curing agent with a specific gravity of 10% of PDMS, vacuum and continue stirring until no bubbles are generated. S1.2: Spray silicone release agent onto the glass slide, heat it on a 150° oven for 10 minutes to dry it, then spin the prepared polymer colloid onto the glass slide at a speed of 400 r / min for two minutes on a spin coater to form a uniformly distributed colloid base, and then heat it on a 150° oven for 5 minutes to cure it into a film of uniform thickness. S1.3: Arrange the conductive film as follows Figure 1 The image was etched using a 60kHz laser at a speed of 2000mm / s, followed by edge trimming using a 20kHz laser at a speed of 20mm / s. Next, a chemical plating solution was prepared by mixing water, copper plating solution component A, and copper plating solution component B in a weight ratio of 15:2:1 and stirring thoroughly. The laser-treated film was then placed in the solution, sealed with tin foil, and placed in a constant temperature chamber set at 30°C and 30% humidity for chemical plating for 4 hours. Through this process, a copper plating layer was uniformly deposited on the substrate, forming a dense conductive film. After chemical plating, the substrate was carefully removed and thoroughly cleaned and dried. Finally, a peeling operation was performed along the previously high-energy laser-etched edges to gently and precisely peel out the individual sensor units, completing the fabrication of the sensing unit. S1.4: To further facilitate the mechanical-electrical testing of the sensing unit, it is necessary to encapsulate the sensing unit. First, polydimethylsiloxane and curing agent are mixed at a weight ratio of 10:1, stirred evenly, and then vacuum degassing is performed to remove air bubbles from the mixture. Subsequently, the treated PDMS mixture is evenly coated onto a glass substrate that has been sprayed with silicone release agent and dried using a spin coater, and then heated and cured on a 120°C heating stage. The cured flexible film substrate is then laser-cut, cut to a radius of 45 mm, and the excess is peeled off. Then, the electrodes are thermally transferred. In the electrode preparation process, the copper / PI film is first cut to an appropriate size, and identical pieces are cut... Water-soluble adhesive tape of the specified size is used to adhere the material to the copper-clad layer. To ensure the flatness of the adhesive, after fixing the adhered material onto the glass plate, any gaps between the material and the glass plate need to be removed by pressing to avoid affecting the subsequent laser cutting effect. The PI layer of the material to be cut is placed face up on the laser cutting platform, and the distance between the laser emitting lens and the platform is carefully adjusted to ensure that the laser can be correctly focused on the surface of the object to be cut. The designed electrode pattern is imported into the laser marking software, and the laser processing parameters are set according to the actual situation: 55 processing times, processing speed of 300mm / s, power set to 55%, frequency adjusted to 20KHz, and the on-time delay is -230μs. The laser was set to turn off with a delay of 200 μs, and both the end delay and corner delay were set to 100 μs. The jump speed was set to 3000 mm / s. After turning on the red light profile, the laser was precisely aligned with the material to be cut and cutting began. The cutting effect was good; the laser only cut through the PI layer and copper layer, while the water-soluble adhesive tape was unaffected. After cutting, excess material was removed from the sample, and the surface of the cut sample was cleaned using appropriate methods to ensure that there was no dust or impurities. After microscopic observation, the excess copper foil and water-soluble adhesive tape were successfully separated, completing the electrode structure preparation experiment. The prepared electrode PI layer was pressed tightly against the center of the prepared circular flexible substrate and placed on a 120°C heating stage, with 500 grams of pressure applied. A heavy weight was applied for at least ten minutes of heat transfer to ensure a strong bond between the electrode and the substrate. After the heat transfer, the electrode was carefully removed from the heating plate and rinsed with running water. The water-soluble adhesive on the surface gradually dissolved and disappeared, leaving a clean electrode structure. Finally, the cleaned electrode was dried in a 60°C oven. Soldering was then performed on the transferred electrode surface to ensure a reliable and stable connection between the electrode and the sensor unit. Simultaneously, the stripped independent Y-shaped sensor unit was soldered onto the electrode. To facilitate subsequent electrical testing, a section of enameled wire was soldered to the other end of the electrode to connect to the external circuitry, resulting in the final product shown below. Figure 2The sensing unit is shown below. Finally, a layer of PDMS colloid is spin-coated onto the surface of the sensing unit and then cured by heat. This effectively encapsulates the sensing unit, protecting the sensor and improving its performance. The entire manufacturing process is now successfully completed. S1.5: In COMSOL Multiphysics Simulation software, perform 1:1 modeling and simulation according to the dimensions of the prepared sensing unit; and simulate the strain and stress distribution of the sensing unit when it experiences strain at different angles, such as... Figure 4 , 5 As shown, this confirms that the sensing unit has the ability to recognize stretching at different angles; S1.6: The packaged sensing unit was subjected to 30% strain stretching at different angles on a mechanical testing instrument. Based on the collected resistance data, the strain curves fitted by the three sensors in the sensing unit were obtained as follows: Figure 6 As shown; subsequently, at a fixed strain angle of 45°, the resistance changes of the three sensors in the sensing unit were recorded over three periods with strain increments of 4% from 0% to 32%. Figure 7 As shown.

[0036] A multilayer stress sensor fabricated using laser direct writing technology includes the following steps: S2.1: Mix PDMS and ATO in a weight ratio of 100:5 and stir thoroughly to ensure that the dopant is evenly distributed in the substrate to form a flexible polymer colloid doped with a photoactivated catalyst. Then add 10% of PDMS as a curing agent, vacuum and continue stirring until no bubbles are generated. S2.2: Spray silicone release agent onto the surface of a scaled-down aircraft model and dry it in a 60°C oven for 20 minutes; evenly apply the prepared conductive colloid to the surface of the aircraft model and place it in a 60°C oven for one hour to cure; the final result is as follows. Figure 8 As shown, a uniform thin film is formed on the surface of the model; S2.3: Arrange the conductive film as follows Figure 1 The model was etched multiple times using a 60kHz laser at a speed of 2000mm / s. The optical image of the processed model surface is shown in Figure 9. Next, water, copper plating solution component A, and copper plating solution component B were mixed in a weight ratio of 15:2:1 to prepare the chemical plating solution, which was then thoroughly stirred. The laser-treated aircraft model was placed in the solution, sealed with tin foil, and then placed in a constant temperature chamber set at 30°C and 30% humidity for chemical plating for 4 hours. Through this process, a copper plating layer was uniformly deposited on the substrate, forming a dense conductive film. After chemical plating was completed, the model was carefully removed and thoroughly cleaned and dried. Figure 10 The large-scale fabrication of the three-dimensional curved surface sensing unit array is shown.

[0037] Obviously, the embodiments described above are merely some, not all, embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0038] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0039] It should be noted that the terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented in sequences other than those illustrated or described herein.

[0040] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0041] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A multilayer stress sensor prepared based on a laser direct writing technique, characterized in that: The multilayer stress sensor comprises two conductive layers, i.e. an upper layer and a lower layer, and the substrate of the lower layer is composed of a mixed colloid of a flexible polymer, conductive nanomaterial and a catalyst; the upper layer is a metal conductive layer closely connected with the lower layer formed by laser catalytic chemical plating.

2. The multilayer stress sensor prepared based on the laser direct writing technology according to claim 1, characterized in that: The multilayer stress sensor has a "Y" shape, and three sensors extend from the center point along three different angles, and the center points of the three sensors are connected with each other.

3. The multilayer stress sensor prepared based on the laser direct writing technology according to claim 1, characterized in that: The multilayer stress sensor is prepared on a doped flexible substrate by using a laser direct writing technology.

4. The multilayer stress sensor prepared based on the laser direct writing technology according to claim 2, characterized in that: The angle between the three sensors and the size of the sensor can be controlled by a laser control file drawn in advance to control the laser etching mode.

5. The multilayer stress sensor prepared based on laser direct writing technology according to claim 2, characterized in that: When the sensor generates strain in a two-dimensional plane, the resistance change trend of the three sensors in the sensor unit has obvious correlation with the strain angle and amplitude.

6. The multilayer stress sensor prepared based on laser direct writing technology according to claim 1, characterized in that: The flexible polymer comprises a polymer such as polydimethylsiloxane and a styrene polymer, which can be used as a doped bearing substrate.

7. The multilayer stress sensor based on laser direct writing technology according to claim 1, wherein: The conductive nanomaterial comprises a nanomaterial with conductivity such as a carbon nanotube and carbon black.

8. The multilayer stress sensor prepared based on laser direct writing technology according to claim 1, characterized in that: The catalyst comprises a material with catalytic acceleration of the chemical plating process such as ATO.

9. A method for preparing a multilayer stress sensor based on laser direct writing technology, comprising the multilayer stress sensor based on laser direct writing technology as claimed in claims 1-8, characterized in that: The preparation steps comprise: S1: The flexible polymer, conductive nanomaterial and photo-activated catalyst are mixed in a certain proportion, and then fully stirred to uniformly distribute the dopant in the substrate to form a conductive flexible polymer colloid doped with a photo-activated catalyst; then a suitable curing agent is added, vacuum is continued, and stirring is continued until no bubbles are generated; S2: A silicon release agent is sprayed on a glass sheet, heated and dried on a baking table, and then the prepared conductive polymer colloid is spin-coated on the glass sheet on a high-speed centrifugal colloid coating machine to form a uniformly distributed colloid, and then placed on a baking table for heating and curing to form a thin film with uniform thickness.

10. S3: The conductive thin film is processed according to the requirements using a laser with appropriate power, and then the surface of the thin film is cleaned with water.

11. S4: The solution required for chemical plating is proportioned and fully stirred, the laser-processed thin film is placed in the solution, sealed and placed in a constant temperature box for chemical plating treatment.

12. S5: The thin film sheet is taken out and cleaned with water, then dried, and the thin film is peeled off from the glass sheet to obtain the required sensor, and the preparation of the strain sensing unit is completed.

13. The method of claim 9, wherein the method is based on laser direct writing technology. In step S1, the weight ratio of the conductive nanomaterial carbon nanotube to the flexible polymer PDMS is 1%-6%, the weight ratio of the photo-activated catalyst ATO to the flexible polymer PDMS is 3%-6%, and the weight ratio of the curing agent to PDMS is 1:10-1:5; in step 2, the drying of the silicon release agent is performed on a baking table at 150°C for 10 minutes, the spin coating step is performed on a high-speed centrifugal spin coater at a speed of 400 r / min for 2 minutes, the baking table temperature is set to 150°C during the heating and curing, and the heating time is 5 minutes; in step 3, the laser treatment is laser activation etching treatment of multiple "Y" type regions using an ultraviolet laser at a laser frequency of 20-60 kHz and a speed of 2000 mm / s, and then cutting treatment of the region edges using a speed of 20 kHz and 10 mm / s; in step 4, the chemical plating solution is configured by mixing water, copper plating liquid component A, and copper plating liquid component B in a mass ratio of 15:2:1, the temperature of the thermostat is set to 30°C, the humidity is 20%, and the chemical plating time is 4 hours.

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