High-integration-level interdigital flexible strain sensing array and preparation method thereof

Abstract

The invention discloses a high-integration-level interdigital flexible strain sensing array and a preparation method thereof. The preparation method comprises the following steps: circularly cutting a flexible thin film through a nanosecond laser to manufacture a thin film substrate with small holes; after the small holes in the film substrate are aligned with the small points of the interdigital array electrode layer silk-screen printing screen plate, an interdigital array upper electrode layer is manufactured through via hole silk-screen printing; covering the cured upper electrode layer of the interdigital array with a protective film, and performing hot pressing and cooling to form an upper packaging layer; after small holes in the back face of the film substrate where the upper packaging layer is installed are aligned with small points of a back face electrode layer silk-screen printing screen plate, an interdigital array lower electrode layer is manufactured through the silk-screen printing technology; and covering the lower electrode layer of the interdigital array with a protective film, and performing hot-pressing packaging to obtain a complete sensing array. According to the invention, the bottleneck that the traditional interdigital array is complex in design and low in integration level is successfully broken through, high integration of the sensor array is realized, and more complex strain monitoring requirements can be met.

Description

Technical Field

[0001] The present invention relates to the field of flexible wearable electronics and micro-nano sensor devices, and particularly to a highly integrated interdigital flexible strain sensing array and a preparation method thereof. Background Art

[0002] The skin is the largest organ of the human body, consisting of multiple layers of different tissues. It can not only sense stimuli such as temperature, pressure, and pain, but also constantly participate in the body's functional activities. The mechanical properties of human skin play an important role in distinguishing healthy skin from unhealthy skin. The strain on the human skin surface is particularly crucial for the early detection of many skin diseases.

[0003] However, traditional mechanical strain sensors have many limitations such as weak wearability, poor direction perception ability, and limited detection area, resulting in problems such as inconvenient use, low detection accuracy, and low detection efficiency. Overcoming these defects has become the key to opening up the market in the field of human skin surface strain detection.

[0004] The emergence of planar interdigital electrode sensing array technology has brought new hope for solving many problems in the sensing field. This technology adopts a unique electrode design. By integrating the electrodes in a staggered arrangement on the same plane, the sensitivity and response ability of the sensor are greatly improved. When the sensing device is closely attached to the skin surface, the planar interdigital electrode sensing array can accurately sense the pressure changes from different directions. This multi-directional pressure sensing ability makes it have broad application prospects in the fields of wearable devices, electronic skin, and medical monitoring. However, the traditional planar interdigital electrode sensing array has complex design, numerous leads, low integration, and poor electrode stability. Summary of the Invention

[0005] To solve the above problems, the present invention provides a highly integrated interdigital flexible strain sensing array with different direction perception abilities and a preparation method thereof, successfully breaking through the bottleneck of the complex design and low integration of the traditional interdigital array, realizing the high integration of the sensor array, and being able to adapt to more complex strain monitoring requirements.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: A preparation method of a highly integrated interdigital flexible strain sensing array includes the following steps: S1. Preparation of a perforated flexible substrate: A thin film substrate with small holes is made by circularly cutting a flexible film with a nanosecond laser. S2. Through-hole screen printing of the upper electrode layer of the interdigital array: After aligning the small holes on the thin film substrate with the printing points of the screen printing stencil of the interdigital array electrode layer, together Place it on the screen printing table, add liquid metal conductive ink, print with a squeegee at a 45° tilt, and dry to obtain the cured interdigital array upper electrode layer; S3. Encapsulation of the interdigital array upper electrode layer Cover the interdigital array upper electrode layer with a protective film, place it at 80 °C and hot press for 90 s, and then cool to form the upper encapsulation layer; S4. Through-hole screen printing of the interdigital array lower electrode layer After aligning the small holes on the reverse side of the film substrate with the small dots of the screen printing stencil of the reverse side electrode layer after the upper encapsulation layer is installed, place them together on the screen printing table, add liquid metal conductive ink, print with a squeegee at a 45-degree tilt, and dry to obtain a film substrate with an interdigital array upper electrode layer and an interdigital array lower electrode layer; S5. Encapsulation of the reverse side electrode layer of the substrate Cover the interdigital array lower electrode layer with a protective film, perform hot press encapsulation to construct the lower encapsulation layer, and obtain a complete sensing array.

[0007] Furthermore, in the step S1, during cyclic cutting, the laser power is 15 W, the cutting speed is 1000 mm / min, and the cutting times are 5 times.

[0008] Furthermore, in the step S1, after cyclic cutting is completed, the film substrate with small holes needs to be placed in a plasma cleaner for plasma cleaning treatment.

[0009] Furthermore, in the step S2, during drying, place it on an 80 °C baking table and heat and dry for 10 - 20 min.

[0010] Furthermore, the flexible film is made of a silicone film or a TPU film.

[0011] Furthermore, the protective film is made of a silicone film or a TPU film.

[0012] The present invention also provides a highly integrated interdigital flexible strain sensing array, which is prepared by using the preparation method of the above-mentioned highly integrated interdigital flexible strain sensing array, and includes an upper encapsulation layer, an interdigital array upper electrode layer, a perforated flexible substrate, an interdigital array lower electrode layer, and a lower encapsulation layer sequentially arranged from top to bottom. The upper encapsulation layer, the interdigital array upper electrode layer, the perforated flexible substrate, the interdigital array lower electrode layer, and the lower encapsulation layer are integrally formed by hot press lamination.

[0013] The strain change directions of the sensing units of the high-integration interdigital flexible strain sensing array of the present invention are different in the two directions of longitudinal and transverse stretching, which can effectively distinguish different directions of strain, thus significantly improving the functional diversity of the sensor. Through the via printing technology, the problem of numerous leads in the traditional interdigital sensor array is effectively solved, enabling the sensing array to achieve high integration. The heating interconnection of the encapsulation layer realizes the flexible encapsulation of the array, ensuring the ultra-high flexibility of the array to adapt to various forms of skin surface adhesion and expanding the application of the flexible array on the human skin surface. Using the full screen printing technology, the preparation operation is simple and the cost is low, which is conducive to large-scale production and commercial promotion. Such a flexible strain sensing array can be widely applied to scenarios that require pressure insensitivity, high stability, and high sensitivity, providing an effective solution for improving the performance and reliability of equipment. Description of the Drawings

[0014] By reading the following detailed description of the non-limiting embodiments with reference to the accompanying drawings, other features, objects, and advantages of the present invention will become more apparent: Figure 1 It is a schematic structural diagram of each layer in a high-integration interdigital flexible strain sensing array according to an embodiment of the present invention; Figure 2 It is a schematic diagram of the liquid metal via structure during screen printing; Figure 3 It is a schematic diagram of the principle of the present invention with different direction sensing capabilities; Figure 4 It is the "strain-resistance" experimental test result of the via printing electrode layer in an embodiment of the present invention; Figure 5 It is the cyclic test result of the line resistance value under 100% tensile strain in an embodiment of the present invention; In the figure: 1 - upper encapsulation layer; 2 - upper electrode layer of the interdigital array; 3 - perforated flexible substrate; 4 - lower electrode layer of the interdigital array; 5 - lower encapsulation layer; 6 - via. Detailed Embodiments

[0015] The present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made. These all belong to the protection scope of the present invention.

[0016] In order to break through the bottleneck of complex traditional interdigital array design and low integration, the present invention provides a preparation method for a highly integrated interdigital flexible strain sensing array, innovatively introducing a via technology, which not only simplifies the wiring structure of the sensor, reduces the density of the number of leads, thereby improving the overall mechanical and electrical properties, but also realizes the high integration of the sensor array, enabling the sensor to adapt to more complex strain monitoring requirements while maintaining high sensitivity and stability. Specifically, the preparation method includes the following steps: S1. Preparation of a perforated flexible substrate: The perforated flexible substrate can be fabricated by cutting with a nanosecond laser or by die casting. In this embodiment, taking the cutting with a nanosecond laser as an example for detailed description: During operation, the shape of the target substrate with small holes is imported into the nanosecond laser. Take a silicone film with a suitable size and a thickness of 0.3 mm, adsorb it on the laser etching platform through vacuum, and perform 5 cycles of cutting with a laser power of 15 W and a cutting speed of 1000 mm / min. After all the contours are cut, remove the silicone film and place it in a plasma cleaner for plasma cleaning treatment to obtain a thin film substrate with small holes, and set it aside for use; S2. Via printing of the upper electrode layer of the interdigital array: The via printing of the upper electrode layer of the interdigital array can be carried out by screen printing technology or by 3D printing (such as direct ink writing, etc.). Screen printing technology has the advantages of simple operation, low equipment cost, and large-area printing, and can perform patterned printing on various flexible materials to meet the preparation requirements of the flexible strain sensing array. Moreover, this technology can precisely control the printing thickness and pattern accuracy, ensuring the quality of the electrode layer, the base layer, and the encapsulation layer, thereby guaranteeing the performance stability and detection accuracy of the sensor. Therefore, in this embodiment, taking the screen printing technology as an example for detailed description: During operation, place the thin film substrate on the screen printing table, then fix the screen printing stencil of the interdigital array electrode layer above the thin film substrate, and align the small dots on the screen printing stencil with the small holes on the thin film substrate. Then pour the liquid metal conductive ink onto the screen printing stencil, and perform inclined printing at 45° with a squeegee to obtain a silicone-interdigital array electrode layer film. Then, place it on an 80°C drying table and heat it for 10 - 20 min to obtain a cured silicone-interdigital array electrode layer structure.

[0017] S3. Encapsulation of the interdigital array electrode layer Cover the cured silicone-interdigital array electrode layer structure with a TPU protective film, place it under 80°C for hot pressing for 90 s, and then cool it to form an upper encapsulation layer.

[0018] S4. Via printing of the lower electrode layer of the interdigital array The vias of the upper electrode layer on the interdigital array can be printed using screen printing technology or constructed by 3D printing (such as direct ink writing). In this embodiment, screen printing technology is adopted. During operation, the reverse side of the thin film substrate with the upper encapsulation layer installed is placed on the screen printing table. Then, the screen printing stencil of the reverse side electrode layer is fixed above the substrate, and the dots on the screen printing stencil are aligned with the small holes on the thin film substrate. Then, the liquid metal conductive ink is poured onto the screen printing stencil, and a 45º inclined printing is performed using a squeegee. After printing, the thin film substrate with the upper electrode layer and the lower electrode layer of the interdigital array is placed on an 80°C drying table and heated and dried for 10 - 20 minutes.

[0019] S5. Encapsulation of the reverse side electrode layer of the substrate Cover the protective film on the lower electrode layer of the interdigital array, and perform thermal compression encapsulation on the lower electrode layer of the interdigital array according to the steps similar to S3 to construct the lower encapsulation layer and obtain a complete sensing array.

[0020] Preferably, the upper electrode layer and the lower electrode layer of the interdigital array in the present invention can adopt a structural design with more fingers and smaller finger spacing to improve the strain sensing sensitivity. The unit area of the interdigital sensor can be reduced, or the printing accuracy can be optimized to reduce the sensor line width and line spacing to improve the integration degree of the sensing array. At the same time, different array shapes can be designed according to the needs of the detection part to increase the wearing comfort.

[0021] As Figure 1 shown, an interdigital flexible strain sensing array with different direction sensing capabilities provided by an embodiment of the present invention includes an upper encapsulation layer 1, an upper electrode layer 2 of the interdigital array, a perforated flexible substrate 3, a lower electrode layer 4 of the interdigital array, and a lower encapsulation layer 5 arranged in sequence from top to bottom. The upper encapsulation layer 1, the upper electrode layer 2 of the interdigital array, the perforated flexible substrate 3, the lower electrode layer 4 of the interdigital array, and the lower encapsulation layer 5 are integrally formed by thermal compression. The functional layers are closely attached and work together, thereby ensuring the high integration degree of the strain sensing array. At the same time, since the strain change directions of the upper electrode layer 2 and the lower electrode layer 4 of the interdigital array are different in two directions, the different directions of the strain can be effectively distinguished, thus significantly improving the functional diversity of the sensor. In this embodiment, the perforated flexible substrate 3 can adopt a 0.3 mm silicone film or a TPU film. The upper electrode layer 2 and the lower electrode layer 4 of the interdigital array can be made of liquid metal conductive ink or indium tin alloy. The upper encapsulation layer 1 and the lower encapsulation layer 5 adopt silicone film or TPU film, etc.

[0022] The liquid metal via stretching experiment materials for the upper electrode layer of the interdigital array, the vias, and the lower electrode layer of the interdigital array are composed of Figure 2It can be observed that the vias are filled with liquid metal conductive ink, so that the upper electrode layer of the interdigital array and the lower electrode layer of the interdigital array form an electrical path through the conductive vias, realizing the "off-plane integration" of the wires.

[0023] Figure 3 It can be observed that the original interdigitated electrodes are shown in a. When the stretching direction is shown in b, the distance between the electrodes becomes larger. According to the capacitance formula ( is the dielectric constant, is the electrode facing area, is the electrostatic force constant, is the electrode spacing), the capacitance value decreases when the distance increases, so in this case the capacitance value decreases; when the stretching direction is as shown in c, the distance between the electrodes decreases, and the capacitance value increases. It can be found that the change trends of the capacitance values ​​in the above two cases are different, so the stretching direction can be distinguished accordingly.

[0024] Figure 4 It can be observed that the relative change of the resistance of the liquid metal of the interdigital flexible strain sensing array with different directional sensing capabilities under different strains of the present invention. When the strain is equal to 100%, the relative change of the resistance is only 5%. The change of resistance is almost negligible.

[0025] Figure 5 It can be observed that when the interdigitated flexible strain sensor array with different directional sensing capabilities of the present invention is subjected to 100% tensile strain, as the number of cyclic tests increases, the line resistance in the sensor array changes accordingly. This change reflects the strain response characteristics of the material during repeated stretching and release. Although the resistance changes after each cycle, the overall change is not significant, which shows that the sensor array has good stability and reliability.

[0026] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A preparation method of a highly integrated interdigital flexible strain sensing array, characterized in that: It includes the following steps: S1. Preparation of a perforated flexible substrate: A thin film substrate with small holes is fabricated by circularly cutting a flexible film with a nanosecond laser; S2. Through-hole screen printing of the upper electrode layer of the interdigital array: After aligning the small holes on the thin film substrate with the printing points of the screen printing stencil of the interdigital array electrode layer, the upper electrode layer of the interdigital array is fabricated by screen printing technology; S3. Encapsulation of the upper electrode layer of the interdigital array A protective film is covered on the upper electrode layer of the interdigital array, and it is hot-pressed at 80 °C for 90 s and then cooled to form an upper encapsulation layer; S4. Through-hole screen printing of the lower electrode layer of the interdigital array After aligning the small holes on the reverse side of the thin film substrate with the small dots of the screen printing stencil of the reverse side electrode layer after the installation of the upper encapsulation layer, the lower electrode layer of the interdigital array is fabricated by screen printing technology to obtain a thin film substrate with an upper electrode layer of the interdigital array and a lower electrode layer of the interdigital array; S5. Encapsulation of the reverse side electrode layer of the substrate A protective film is covered on the lower electrode layer of the interdigital array, and hot-press encapsulation is performed to construct a lower encapsulation layer to obtain a complete sensing array.

2. The preparation method of a highly integrated interdigital flexible strain sensing array according to claim 1, characterized in that: In the step S1, during circular cutting, the laser power is 15 W, the cutting speed is 1000 mm / min, and the cutting times are 5 times.

3. The preparation method of a highly integrated interdigital flexible strain sensing array according to claim 1, characterized in that: In the step S1, after circular cutting is completed, the thin film substrate with small holes needs to be placed in a plasma cleaner for plasma cleaning treatment.

4. The preparation method of a highly integrated interdigital flexible strain sensing array according to claim 1, characterized in that: In the step S2, after aligning the small holes on the thin film substrate with the printing points of the screen printing stencil of the interdigital array electrode layer, they are placed on the screen printing table together, liquid metal conductive ink is added, and printing is performed with a squeegee inclined at 45º and dried to obtain the upper electrode layer of the interdigital array. During drying, it is heated and dried on an 80 °C drying table for 10 - 20 min.

5. The preparation method of a highly integrated interdigital flexible strain sensing array according to claim 1, characterized in that: The flexible film is made of a silicone film or a TPU film.

6. The preparation method of a highly integrated interdigital flexible strain sensing array according to claim 1, characterized in that: The protective film is made of a silicone film or a TPU film.

7. A highly integrated interdigital flexible strain sensing array, characterized in that: It is prepared by using the preparation method of the highly integrated interdigital flexible strain sensing array according to any one of claims 1 - 6.

8. The highly integrated interdigital flexible strain sensing array according to claim 7, characterized in that: It includes an upper encapsulation layer, an upper electrode layer of the interdigital array, a perforated flexible substrate, a lower electrode layer of the interdigital array, and a lower encapsulation layer which are arranged in sequence from top to bottom. The upper encapsulation layer, the upper electrode layer of the interdigital array, the perforated flexible substrate, the lower electrode layer of the interdigital array, and the lower encapsulation layer are compounded into one body by hot pressing.

Images