Composite structure, preparation method, packaging method, water immersion sensor and application

Abstract

The application discloses a composite structure, a preparation method, a packaging method, a water immersion sensor and application, and comprises a POF base layer, an Ag layer, a Ni3(HITP)2 layer and a Nb2C MXene layer; the Ag-O bond connection is formed between the POF base layer and the Ag layer; the Ag-N bond connection is formed between the Ag layer and the Ni3(HITP)2 layer; the Ag-Cl bond connection is formed between the Ag layer and the Nb2C MXene layer; the Ni-O-Nb coordination bond and the pi-pi bond between aromatic skeletons are formed between the Ni3(HITP)2 layer and the Nb2C MXene layer to realize the connection; the Ni-O-C coordination bond connection is formed between the Ni3(HITP)2 layer and the POF base layer; and the Nb-O-C coordination bond connection is formed between the Nb2C MXene layer and the POF base layer. The application realizes accurate and continuous quantitative detection of a water immersion solution, and the sensing response law is stable and has good repeatability.

Description

Technical Field

[0001] This invention relates to a composite structure, preparation method, packaging method, and water immersion sensor and its application, belonging to the fields of materials science, flexible electronics, and wearable technology. Background Technology

[0002] Flexible pressure sensors convert mechanical forces into electrical signals and are widely used in wearable devices, smart interactions, and biomimetic robots due to their good fit and high sensitivity. Water immersion sensors based on the hydrogel swelling effect are an important branch of flexible pressure sensors. Their conventional structure involves filling the etched area of ​​a MEMS pressure sensor with hydrogel. The swelling deformation generated after the hydrogel absorbs the solution compresses the sensing unit, driving the flexible diaphragm to bend, and thus converting the swelling amount into a recognizable electrical signal. However, this traditional structure has significant drawbacks: long-term compression of the hydrogel easily leads to irreversible deformation, causing sensor signal drift and distortion, making it difficult to meet the long-term stable monitoring requirements of wearable devices. Therefore, developing novel functional materials and device structures based on the swelling sensing mechanism to improve overall sensing performance has become a research hotspot in the field of flexible sensing.

[0003] Existing technologies disclose hydrogel-based swelling sensors. For example, the literature "Enzyme-Functionalized Piezoresistive Hydrogel Biosensors for the Detection of Urea" (Sensors, 2019, 19, 2858) reports a water immersion sensor. This sensor encapsulates a urease-loaded hydrogel within the etched area of ​​a piezoresistive sensor. The hydrogel swells due to the alkaline environment generated by urea hydrolysis, squeezing the diaphragm to generate a pressure signal. This device has a detection range of 1–20 mmol / L, but suffers from slow response, with a response time as long as 4 hours and a recovery time of 20 hours. Furthermore, the hydrogel is prone to dehydration and failure during long-term storage, leading to sensor performance degradation and a short device lifespan.

[0004] Another paper, "Porosity Engineering of Dried Smart Poly (N-isopropylacrylamide) Hydrogels for Gas Sensing" (Biomacromolecules, 2024, 25, 2715-2727), discloses a porous hydrogel-based gas sensor. This sensor utilizes the swelling effect of porous hydrogels adsorbing volatile organic compounds, combined with a piezoresistive chip to detect membrane deformation, to achieve gas detection. The detection range for acetone is 20–100 ppm, with a response time of 40 s. While this approach improves adsorption and response speed through its porous structure, the reduced porous structure decreases the effective contact area between the hydrogel and the sensing substrate, resulting in insufficient output signal strength and limited sensing sensitivity. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention provides a composite structure, a preparation method, a packaging method, a water immersion sensor, and its application.

[0006] To achieve the above objectives, the present invention employs a POF / Ag / Ni3(HITP)2 / Nb2C MXene wrinkled composite structure, comprising a POF (Polyolefin oriented film, multilayer co-extruded polyolefin heat shrinkable film) base layer, an Ag layer, a Ni3(HITP)2 layer and an Nb2C MXene layer stacked sequentially from bottom to top;

[0007] Between the POF substrate and the Ag layer, the hydroxyl groups on the surface of the POF substrate are tightly bonded to silver atoms through van der Waals forces, forming weak Ag-O bonds with a bond length of 3.0~3.6 Å. This ensures interfacial adhesion while reducing interfacial contact resistance, preventing electrode layer peeling, and providing stable physical support for the multilayer structure.

[0008] Between the Ag layer and the Ni3(HITP)2 layer, stable Ag-N bonds are formed between silver atoms and nitrogen atoms in the Ni3(HITP)2 layer. The bond length is preferably 2.6~3.0 Å. Within this bond length range, efficient coupling of interface electrons can be achieved, which significantly improves the interface bonding strength and charge transport rate, and effectively suppresses signal noise.

[0009] The Ag layer and the Nb2C MXene layer are connected by Ag-Cl bonds formed by silver atoms and chlorine atoms doped in the Nb2C MXene layer. The bond length is preferably 2.6~3.2 Å. The appropriate bond length ensures the stability of the interface bonding. At the same time, the electronegativity of halogen atoms is used to optimize the interface band structure and reduce the carrier transport barrier.

[0010] Between the Ni3(HITP)2 layer and the Nb2C MXene layer, Ni-O-Nb coordination bonds are formed between the nickel atoms of the Ni3(HITP)2 layer and the niobium atoms on the surface oxide layer of the Nb2C MXene layer. The bond length is preferably 2.2~3.8 Å. Combined with the π–π conjugation between aromatic skeletons, a tight physical contact and chemical anchoring can be maintained within a wide bond length range, which synergistically promotes the rapid transfer and uniform distribution of interfacial charges.

[0011] Between the Ni3(HITP)2 layer and the POF substrate, Ni-OC coordination bonds are formed between the nickel atoms of the Ni3(HITP)2 layer and the hydroxyl groups on the surface of the POF substrate. The bond length is preferably 2.3~3.0 Å. The short-range strong coordination effectively enhances the chemical bonding force between the sensitive layer and the substrate, avoids interlayer failure, and optimizes the energy level matching at the interface.

[0012] The Nb2C MXene layer and the POF substrate are connected by Nb-OC coordination bonds formed by niobium atoms in the Nb2C MXene layer, the carbon skeleton of the POF substrate, and hydroxyl groups on the surface of the POF substrate. The bond length is preferably 2.3~3.2 Å. This bond length ensures strong interlayer interaction while taking into account the interfacial stress buffering capacity, further improving the mechanical stability and electrochemical performance of the composite structure.

[0013] Preferably, the POF substrate has a thickness of 3-25 μm and a wavy folded structure; the spacing between adjacent fold peaks or adjacent fold valleys is 0.5-5 μm, and the height difference between fold peaks and fold valleys is 1-5 μm; the gaps, interior, and top of the folds are all covered with an Ag / Ni3(HITP)2 / Nb2C MXene composite structure; the Ag layer has a thickness of 5-25 μm, the Ni3(HITP)2 layer has a thickness of 0.01-0.1 μm, and the Nb2C MXene layer has a thickness of 0.01-0.1 μm.

[0014] A second aspect of the present invention also provides a method for preparing the POF / Ag / Ni3(HITP)2 / Nb2C MXene wrinkled composite structure, comprising the following steps:

[0015] (1) Take a clean Si substrate, 1.50~2.50 cm long and 1.50~2.50 cm wide; POF heat shrink film, 2.00~3.00 cm long and 2.00~3.00 cm wide;

[0016] The POF heat shrink film is fixed on a clean Si substrate using high-temperature tape. The film is then heated at 150-250 °C for 8-10 seconds using a hot air gun to shrink the POF heat shrink film and completely adhere it to the substrate, thus obtaining a POF substrate layer loaded on the substrate.

[0017] (2) A silver film was deposited on the surface of the POF substrate using a vacuum deposition process to obtain a POF / Ag composite layer based on a Si substrate;

[0018] (3) Take 1~5 mg of washed and dried Ni3(HITP)2 powder, disperse it in a mixed solvent composed of isopropanol and deionized water (the volume ratio of isopropanol to deionized water is 1:(1~2)), and sonicate it until it is uniformly dispersed to obtain Ni3(HITP)2 electrodeposition solution; in Ni3(HITP)2 electrodeposition solution, use a platinum sheet as the positive electrode and the POF / Ag composite layer obtained in step (2) as the negative electrode, and perform electrodeposition under a constant voltage of 0.5~10 V to obtain a POF / Ag / Ni3(HITP)2 composite layer based on a Si substrate;

[0019] (4) Take 1~20 μL of solution with a concentration of 2 mg·mL -1 Nb2C MXene aqueous solution was applied to the surface of the POF / Ag / Ni3(HITP)2 composite layer at a speed of 2000~3000 r·min. -1 Spin coating was performed at a rotation speed of 20~45 s to obtain a POF / Ag / Ni3(HITP)2 / Nb2C MXene composite structure;

[0020] (5) The composite structure obtained in step (4) is peeled off from the Si substrate and placed in an oven at 80~130 ℃ for 3~30 min. After heat shrinking deformation, a POF / Ag / Ni3(HITP)2 / Nb2C MXene wrinkled composite structure is formed.

[0021] A third aspect of the present invention also provides a planar interdigitated sensitive electrode pair, including a pair of interdigitated electrodes and pads (Pad1, Pad2) respectively disposed at the ends of the interdigitated electrodes.

[0022] The surface of the interdigitated electrode has the wrinkled composite structure described above or the wrinkled composite structure prepared by the preparation method.

[0023] Before heat shrinking, the linewidth of the interdigital electrode is 10~30 μm and the line spacing is 100~250 μm; after heat shrinking, the linewidth of the interdigital electrode is 5~15 μm and the line spacing is 55~150 μm.

[0024] A fourth aspect of the present invention also provides a method for fabricating the planar interdigitated sensitive electrode pair, which further includes a photolithography patterning step after the POF substrate is prepared according to step (1) and before step (2):

[0025] Positive photoresist is spin-coated onto the surface of the POF substrate, followed by pre-baking at 82-87 ℃ for 4-6 min, exposure pattern transfer in a photolithography machine, development in a developer for 25-35 s, rinsing with deionized water, and baking at 72-78 ℃ for 4-6 min. After completing the photolithography pattern, steps (2) to (5) are performed. Finally, the product is immersed in an NMP (N-Methyl-2-pyrrolidone) solution for desizing to obtain the planar interdigitated sensitive electrode pair.

[0026] In a fifth aspect, the present invention also provides a sensing module comprising, from bottom to top, a base, a PAM (polyacrylamide) hydrogel, an interdigitated electrode pair, a lead frame, and a cover plate, wherein the interdigitated electrode pair is the planar interdigitated sensitive electrode pair described above or the planar interdigitated sensitive electrode pair prepared by the preparation method described above.

[0027] The base has a hollow structure, and the PAM hydrogel fills the hollow structure;

[0028] The planar interdigitated sensitive electrode pair is fixedly installed on the base, with the interdigitated area of ​​the planar interdigitated sensitive electrode pair facing the hollow structure and in contact with the PAM hydrogel;

[0029] The lead frame is fixed to the planar interdigitated sensitive electrode pair, and the pins of the lead frame extend to the slot of the base.

[0030] The cover plate is fastened to the top of the lead frame. The cover plate and the base are positioned and prevented from shifting by interlocking with the groove and the slot. The cover plate has a through hole, which is directly opposite the sensing area of ​​the sensitive membrane of the planar interdigitated sensitive electrode pair.

[0031] A sixth aspect of the present invention also provides a method for packaging the aforementioned sensing module, comprising the following steps:

[0032] (1) The planar interdigitated sensitive electrode pair is bonded and fixed to the base using DAF (Die Attach Film) adhesive, so that the interdigitated area is aligned with the hollow structure of the base; the pads of the planar interdigitated sensitive electrode pair are electrically connected to the lead frame using conductive silver paste, conductive adhesive or carbon cloth.

[0033] (2) Fill the hollow structure of the base with PAM hydrogel so that the PAM hydrogel is in full contact with the planar interdigitated sensitive electrode pair;

[0034] (3) Apply sealant to the joint between the cover plate and the base. The sealant is epoxy resin or silicone rubber and is cured at room temperature for 16-32 hours.

[0035] (4) Inject sealing material into the potting mold until the sealing material completely covers the cover plate, and cure again at room temperature for 16~32 h to complete the overall encapsulation.

[0036] Specifically, the packaging method of the sensing module includes:

[0037] The Pad1 and Pad2 pads of the planar interdigitated sensitive electrode pair are electrically connected to the lead frame through connectors, which include conductive silver paste, conductive adhesive, or carbon cloth. First, double-sided adhesive is applied to the base surface, and the interdigitated sensing areas of the planar interdigitated sensitive electrode pair are aligned with the hollow structure of the base to complete the electrode alignment pre-assembly. Then, sealant is used to initially bond and fix the planar interdigitated sensitive electrode pair to the base surface.

[0038] For areas where the planar interdigitated sensitive electrode pairs have uneven or raised contact surfaces with the base, DAF adhesive, such as epoxy resin or 502 glue, is applied for secondary bonding and sealing reinforcement to eliminate gaps. Simultaneously, excess POF heat-shrink film edges are embedded into the first groove of the base, and DAF adhesive is applied around the first groove to complete a third sealing protection, further improving structural fit and sealing. After electrode fixing and multiple sealing, the lead extensions of the lead frame are inserted into the slots of the base, and the cover plate is fastened to complete the initial structural assembly. Subsequently, PAM hydrogel is cut into sheet-like structures that match the shape and size of the base's hollow structure and neatly filled into the hollow area to ensure full contact between the hydrogel and the interdigitated electrodes.

[0039] A sealing material, such as epoxy resin or silicone rubber, is applied to the joint between the cover plate and the base. This sealing material penetrates and fills the internal grooves of the base, achieving initial encapsulation of the sensor's internal structure. It is then cured at room temperature for 16-32 hours, completing the first curing process. Next, sealing material is added to the potting mold until the cover plate is completely covered, performing a second potting and encapsulation of the sensor. This is followed by another 16-32 hours of curing at room temperature, completing the second curing process. After this double curing and encapsulation, the entire sensor structure is encapsulated within the sealing material, and the lead frame extends to the outside of the encapsulation body via the base slot, ensuring electrical lead-out while achieving a fully sealed structure. This encapsulation process ensures a tight and close fit to the sensor's internal structure, with an internal void ratio of less than 10% after encapsulation. This reduces encapsulation gaps, air leakage, water leakage, and structural loosening, effectively guaranteeing the long-term stability and reliability of the sensor.

[0040] A seventh aspect of the present invention also provides a water immersion sensor, comprising a substrate, a USB power supply module, a power management module, a microprocessor module, a data acquisition module, a data signal processing module, a storage module, a base, and the aforementioned sensing module or the sensing module obtained by the aforementioned packaging method.

[0041] The sensing module is used to sense the external solution and convert the pressure signal generated by swelling into an electrical signal.

[0042] The acquisition module is electrically connected to the sensing module and is used to acquire the electrical signals output by the sensing module.

[0043] The data signal processing module has a built-in AD conversion unit and a data processing unit. The data signal processing module is electrically connected to the acquisition module and is used to convert the acquired analog electrical signals into digital signals and complete data processing.

[0044] The storage module is electrically connected to the data signal processing module and is used to store the detection data processed by the data signal processing module.

[0045] The microprocessor module is electrically connected to the acquisition module, data signal processing module, storage module and power management module respectively, and is used to issue control commands to each module and coordinate the working status of each module;

[0046] The USB power supply module is electrically connected to the power management module, which provides power to the sensing module, acquisition module, data signal processing module, storage module, and microprocessor module respectively.

[0047] The base is used to support and fix the substrate and various functional modules. Through its internal integrated circuit layout, mechanical connection and electrical conduction between the modules are realized.

[0048] The functional modules are electrically connected on the base through tin solder balls, copper-filled Si vias, and PI adhesive printed copper wires. The gaps between the modules are filled with polyimide to form an overall package shell.

[0049] Furthermore, the sensing module is configured with a total of two pins: a positive pin and a negative pin.

[0050] The storage module is configured with a total of eight pins: power supply 1, ground 1, data input 1, data output 1, debug input 1, debug output 1, reset 1, and clock 1.

[0051] The data signal processing module is configured with eight pins: power supply pin 2, ground pin 2, data input pin 2, data output pin 2, debug input pin 2, debug output pin 2, reset pin 2, and clock pin 2.

[0052] The microprocessor module is configured with three power supply pins, three ground pins, three data input pins, three data output pins, three debug input pins, three debug output pins, three reset pins, and three clock pins, for a total of eight pins.

[0053] The acquisition module is configured with four power supply pins, four ground pins, four data input pins, four data output pins, four debug input pins, four debug output pins, four reset pins, and four clock pins, for a total of eight pins.

[0054] The power management module is configured with ten pins: power supply five, ground five, data input five, data output five, debug input five, debug output five, data receive positive one, data receive negative one, reset five, and clock five.

[0055] The substrate is configured with power supply, ground, data input, data output, data receive positive 1, data receive negative 1, positive 2, negative 2, debug input 1, debug output 1, debug input 2, debug output 2, debug input 3, debug output 3, debug input 4, debug output 4, debug input 5, debug output 5, reset, and clock, for a total of twenty pins;

[0056] The USB power supply module is configured with four pins: power supply six, ground six, data reception positive two, and data reception negative two.

[0057] The modules are electrically interconnected using a combination of methods, including side traces, flip-chip bonding with solder balls, copper-filled Si vias, and PI printed copper conductors. The specific connection relationships are as follows:

[0058] Between the storage module and the data signal processing module: the power supply 1 and ground 1 of the storage module are connected to the power supply 2 and ground 2 of the data signal processing module via side traces on the chip; the reset 1 and clock 1 pins of the storage module are flip-chip bonded to the reset 2 and clock 2 pins of the data signal processing module via solder balls; the data input 1 of the storage module is connected to the data output 2 of the data signal processing module, and the data output 1 of the storage module is connected to the data input 2 of the data signal processing module; the debug input 1 and debug output 1 of the storage module pass through the data signal processing module, the microprocessor module, the acquisition module and the power management module in sequence via Si vias, and are bonded to the debug input 1 and debug output 1 pins of the substrate via solder balls and copper traces on the board.

[0059] Between the data signal processing module and the microprocessor module: Power supply pin 2 and ground pin 2 of the data signal processing module are connected to power supply pin 3 and ground pin 3 of the microprocessor module via side traces on the chip; Reset pin 2 and clock pin 2 of the data signal processing module are flip-chip bonded to reset pin 3 and clock pin 3 of the microprocessor module via solder balls; Data input pin 2 of the data signal processing module is connected to data output pin 3 of the microprocessor module, and data output pin 2 of the data signal processing module is connected to data input pin 3 of the microprocessor module; Debug input pin 2 and debug output pin 2 of the data signal processing module pass through the microprocessor module, acquisition module, and power management module sequentially via Si vias, and are bonded to debug input pin 2 and debug output pin 2 of the substrate via solder balls and copper traces on the board.

[0060] Between the microprocessor module and the acquisition module: the power supply pin 3 and ground pin 3 of the microprocessor module are connected to the power supply pin 4 and ground pin 4 of the acquisition module via side traces on the chip; the reset pin 3 and clock pin 3 of the microprocessor module are flip-chip bonded to the reset pin 4 and clock pin 4 of the acquisition module via solder balls; the data input pin 3 of the microprocessor module is connected to the data output pin 4 of the acquisition module, and the data output pin 3 of the microprocessor module is connected to the data input pin 4 of the acquisition module; the debug input pin 3 and debug output pin 3 of the microprocessor module pass through the acquisition module and the power management module sequentially via Si vias, and are bonded to the debug input pin 3 and debug output pin 3 of the substrate via solder balls and copper traces on the board.

[0061] Between the acquisition module and the power management module: Power supply pin 4 and ground pin 4 of the acquisition module are connected to power supply pin 5 and ground pin 5 of the power management module via side traces on the chip; Reset pin 4 and clock pin 4 of the acquisition module are flip-chip bonded to reset pin 5 and clock pin 5 of the power management module via solder balls; Data input pin 4 of the acquisition module is connected to data output pin 5 of the power management module, and data output pin 4 of the acquisition module is connected to data input pin 5 of the power management module; Debug input pin 4 and debug output pin 4 of the acquisition module pass through the power management module via Si vias and are bonded to debug input pin 4 and debug output pin 4 of the substrate via solder balls and copper traces on the board.

[0062] Between the power management module and the substrate: the power supply pin 5 and ground pin 5 of the power management module are connected to the power supply and ground pins of the substrate via side traces on the chip; the reset pin 5 and clock pin 5 of the power management module are flip-chip bonded to the reset pin and clock pin of the substrate via solder balls; the data input pin 5 and data output pin 5 of the power management module are connected to the data input pin and data output pin of the substrate respectively; the data receive positive pin 1, data receive negative pin 1, debug input pin 5, and debug output pin 5 of the power management module are bonded to the corresponding pins of the substrate via solder balls and copper traces on the board layer.

[0063] Between the sensing module and the substrate: the positive and negative pins of the sensing module are connected to the positive and negative pins of the substrate through copper wires printed with PI adhesive.

[0064] Between the USB power supply module and the substrate: the power supply 6, ground 6, data reception positive 2, and data reception negative 2 pins of the USB power supply module are respectively connected to the power supply, ground, data reception positive, and data reception negative pins of the substrate through PI adhesive printed copper wires.

[0065] Between the substrate and the base: the power supply, ground, data input, data output, data receiving positive, data receiving negative, positive terminal two, negative terminal two, debug input one, debug output one, debug input two, debug output two, debug input three, debug output three, debug input four, debug output four, debug input five, debug output five, reset, and clock of the substrate are bonded to the corresponding pad pins of the base one by one through solder balls;

[0066] After all functional modules are assembled, polyimide material is used to fill all gaps between the modules to form a sealed encapsulation shell. The solder balls used are tin solder balls with a diameter controlled between 200 and 400 μm; the Si vias are filled with copper material with a diameter controlled between 10 and 50 μm. The overall encapsulation structure is dense and cavity-free, ensuring stable electrical connections and structural reliability of the device.

[0067] In an eighth aspect, the present invention also provides an application of a sensing module or a water immersion sensor based on the aforementioned sensing module or the aforementioned packaging method in pressure sensing devices, the pressure sensing devices including wearable health monitoring devices, electronic skin, bionic robots and intelligent interactive devices.

[0068] The pressure sensing device can achieve pressure sensing and detection, specifically including the following steps:

[0069] (1) Power on the device and initialize it to obtain the initial capacitance value C0 of the sensing module;

[0070] (2) When the external solution comes into contact with the sensing module, the solution seeps into the PAM hydrogel and causes it to absorb water and swell. The squeezing force generated by the swelling acts on the planar interdigitated sensitive electrode pair, causing the capacitance between the electrodes to change.

[0071] (3) The acquisition module acquires the capacitance signal in real time and transmits it to the data signal processing module. The data signal processing module performs noise reduction and smoothing processing on the signal according to the formula C=0.58△V+C0, where C is the real-time capacitance value in pF; △V is the amount of solution added in μL; and C0 is the initial capacitance value of the device.

[0072] (4) Depending on the working mode, the calculated amount of solution added is stored in the storage module or output to the outside through the external pin.

[0073] The preparation principle of the wrinkled composite structure of the present invention is as follows:

[0074] When preparing the Ni3(HITP)2 electrodeposition solution, Ni3(HITP)2 powder is dispersed in a solvent of isopropanol and deionized water, and ultrasonically treated until uniformly dispersed to form a uniform electrodeposition solution, ensuring that Ni3(HITP)2 crystals can grow directionally on the Ag electrode surface during constant voltage deposition.

[0075] In preparing the POF / Ag structure based on a Si substrate, a Si substrate and a POF heat-shrinkable film are taken, and the POF heat-shrinkable film is fixed to the surface of the Si substrate with high-temperature tape. The film is then heated to pre-shrink and fully adhere to the substrate, resulting in a flat POF substrate layer based on the Si substrate. A planar interdigitated sensitive electrode pair is obtained on the obtained POF substrate layer based on the Si substrate using photolithography. An Ag thin film is then deposited by magnetron sputtering and immersed in an NMP solution to remove the adhesive, resulting in a POF / Ag composite layer based on the Si substrate.

[0076] When preparing the POF / Ag / Ni3(HITP)2 structure based on Si substrate, a constant voltage electrophoretic deposition method is used: the POF / Ag composite layer is used as the negative electrode and the platinum sheet is used as the positive electrode. The prepared Ni3(HITP)2 electrodeposition solution is poured into the electrolytic cell, and the positive and negative electrodes are immersed in the electrodeposition solution for electrochemical deposition. This allows the Ag layer and the Ni3(HITP)2 layer to be connected by Ag-N bonds formed between silver atoms and nitrogen atoms in the Ni3(HITP)2 layer.

[0077] When preparing the POF / Ag / Ni3(HITP)2 / Nb2C MXene composite structure based on a Si substrate, a spin coating method was used: an aqueous solution of Nb2C MXene was coated on the surface of the POF / Ag / Ni3(HITP)2 composite layer, and Nb2C MXene was impregnated into the pores of Ni3(HITP)2 to obtain the POF / Ag / Ni3(HITP)2 / Nb2C MXene composite structure based on a Si substrate;

[0078] When preparing the wrinkled composite structure, the heat shrinking method is used: the composite structure is peeled off from the Si substrate and placed in an oven for heat treatment at 80~130℃ to obtain the wrinkled composite structure. The wrinkles are wavy and the gaps, interior and top of the wrinkles are covered with Ag / Ni3(HITP)2 / Nb2C MXene structure. Specifically, heat treatment enables the following connections: between the POF substrate and the Ag layer, Ag-O bonds are formed between the hydroxyl groups on the surface of the POF substrate and silver atoms; between the Ag layer and the Nb2C MXene layer, Ag-Cl bonds are formed between the silver atoms in the Ag layer and the chlorine atoms doped in the Nb2C MXene layer; between the Ni3(HITP)2 layer and the Nb2C MXene layer, Ni-O-Nb coordination bonds are formed between the nickel atoms in the Ni3(HITP)2 layer and the niobium atoms on the surface oxide layer of the Nb2C MXene layer, and π–π bonds are formed between the aromatic skeletons; between the Ni3(HITP)2 layer and the POF substrate, Ni-OC coordination bonds are formed between the nickel atoms in the Ni3(HITP)2 layer and the hydroxyl groups on the surface of the POF substrate; and between the Nb2C MXene layer and the POF substrate, Nb-OC coordination bonds are formed between the niobium atoms in the Nb2C MXene layer and the carbon skeleton and hydroxyl groups on the surface of the POF substrate.

[0079] The working principle of the POF / Ag / Ni3(HITP)2 / Nb2C MXene wrinkled composite structure of the present invention is as follows:

[0080] The planar interdigitated electrode based on this wrinkled composite structure was used for water immersion sensing. The structural definitions of the symbols in the attached figures are as follows: black rectangle represents the base, orange rectangle represents the POF substrate, blue rectangle represents the PAM hydrogel, green area represents the Ni3(HITP)2 layer, gray area represents the Nb2C MXene layer, white area represents the Ag layer, blue stripes represent PAM segments, and blue arrows indicate the direction of water immersion; red spheres represent positive ions (H+). + and NH4 + The blue spheres represent negative ions (OH-). - and COO - ).

[0081] When not in contact with external solutions, such as Figure 10 As shown in (a), the PAM hydrogel tightly wraps the wrinkled composite structure above, and the overall structure is in a stable equilibrium state. Positive and negative ions are evenly distributed inside the hydrogel, and there is no ion enrichment phenomenon.

[0082] When in contact with external solutions, such as Figure 10As shown in (b), the external solution immerses the hydrogel through the cutout in the sensing module. The hydrogel absorbs water and swells, causing the cross-linked PAM segments inside to extend, resulting in overall volume swelling of the PAM hydrogel. Due to the constraint of the base structure around the sensing module, the swelling deformation of the hydrogel cannot diffuse outwards, but can only exert a mechanical effect upwards and inwards: forming a convex deformation upwards, while simultaneously squeezing the interdigitated electrode structure inwards, increasing the linewidth of the interdigitated electrodes and decreasing the electrode spacing. At the same time, positive and negative ions from the external solution continuously penetrate into the PAM hydrogel, increasing the overall ion concentration of the hydrogel. The originally uniformly distributed positive and negative ions undergo directional migration under the action of the electric field, with positive ions converging towards the negative electrode and negative ions converging towards the positive electrode, and adsorbing onto the outer surface of the wrinkled composite material. This induces corresponding positive and negative charges on the surface of the composite structure, forming a large number of "ion-charge" pairs at the interface between the composite material and the hydrogel, constructing a stable double layer and pseudocapacitive effect, thereby generating a stable sensing capacitance signal.

[0083] When the amount of external solution contact is further increased, such as Figure 10 As shown in (c), the PAM hydrogel continuously absorbs water and swells, further intensifying the swelling deformation and making the upward convexity of the structure more significant. This continuously increases the internal compressive force on the interdigitated electrodes, resulting in a further increase in the linewidth and a further decrease in the line spacing of the interdigitated electrodes. At the same time, more ions penetrate into the hydrogel with the solution, significantly increasing the ion concentration of the system. The number of "ion-charge" pairs generated at the interface increases significantly, and the double layer and pseudocapacitive effect are continuously enhanced, ultimately achieving a regular increase in the sensing capacitance value.

[0084] This invention achieves accurate and continuous quantitative detection of water-immersed solutions by regulating electrode structural parameters through hydrogel swelling and deformation, combined with the capacitance change mechanism induced by ion migration. The sensing response is stable and has good repeatability.

[0085] Compared with the prior art, the beneficial effects of the present invention are:

[0086] 1) Existing traditional water immersion sensors generally suffer from drawbacks such as easy dehydration and aging of the hydrogel, easy distortion of sensing signals, and short device lifespan. In the prior art, the paper "Enzyme-Functionalized Piezoresistive Hydrogel Biosensors for the Detection of Urea" (Sensors, 2019, 19, 2858) discloses an enzyme-functionalized hydrogel urea sensor. Although this approach improves detection specificity through biometric mechanisms, the device response time is as long as 4 hours, which cannot meet the application requirements of real-time dynamic monitoring. To address the above technical problems, this invention utilizes a detachable, modular packaging structure to achieve convenient replacement and refilling of the PAM hydrogel inside the sensing module. This solves the technical problem of traditional integrated packaged sensors becoming unusable due to hydrogel dehydration and failure, thus improving the long-term stability of the device. Meanwhile, this invention utilizes a heat-shrink process to prepare a POF / Ag / Ni3(HITP)2 / Nb2C MXene wrinkled composite structure. This structure possesses an ultra-large specific surface area and a dense nano-wrinkled morphology, which can accelerate the solution wetting rate and interfacial ion transport efficiency. Experimental verification shows that the solution response time of the water immersion sensor of this invention can be shortened to less than 100 s, exhibiting excellent linear response and rapid, stable monitoring capabilities within the 0–3 μL solution detection range. Compared to traditional fixed hydrogel integrated sensors, it has technical advantages in terms of ease of operation, detection timeliness, and long-term stability.

[0087] 2) In the prior art, the paper "Porosity Engineering of Dried Smart Poly (N-isopropylacrylamide) Hydrogels for Gas Sensing" (Biomacromolecules, 2024, 25, 2715-2727) discloses a porous hydrogel sensing structure. This structure utilizes the adsorption of volatile organic compounds by the porous hydrogel to induce swelling and deformation, combined with a piezoresistive sensor for signal detection, achieving a response time of up to 40 s for acetone gas. However, this porous structure significantly reduces the effective contact area between the hydrogel and the sensing substrate, resulting in attenuation of the pressure signal output amplitude and limitations in sensing sensitivity and detection accuracy. To address this, this invention employs a combination of electrophoretic deposition and spin-coating processes to sequentially construct a Ni3(HITP)2 functional layer and a Nb2C MXene functional layer on the surface of the Ag interdigitated electrode, creating a multilayered, wrinkled composite sensing interface with multiple chemical bonds and excellent interface stability. The composite structure of this invention forms a multi-faceted synergistic interface comprising Ag-N bonds, Ag-Cl bonds, Ni-O-Nb coordination bonds, Ni-OC coordination bonds, Nb-OC coordination bonds, and π-π stacking interactions. Compared to traditional single-sensor materials and simple coating composite structures, it provides an ultra-large specific surface area and abundant interfacial interaction sites, efficiently converting the weak swelling pressure of the hydrogel into a significant change in capacitance signal, thus improving the sensing response sensitivity. Experimental testing shows that the detection sensitivity of the water immersion sensor of this invention can reach 0.576 pF·μL. -1 Meanwhile, XPS characterization results confirmed that the multi-interface synergistic effect of Ag-N bonds with bond lengths of 2.6–3.0 Å, Ni-O-Nb bonds with bond lengths of 2.2–3.8 Å, and interlayer π-π stacking can effectively resist the structural stress caused by repeated swelling-shrinkage cycles of hydrogel, ensuring the structural integrity, operational stability, and signal reproducibility of sensitive interfaces.

[0088] 3) This invention integrates functional units such as the sensing module, signal processing module, storage module, microprocessor module, and USB power supply module onto a substrate carrier. This integrated design overcomes the technical limitations of traditional water immersion sensing devices, which suffer from the separation of the sensing unit and signal processing circuit, low system integration, large device size, and poor portability. It effectively optimizes the electrical connection layout of each functional module, improving the overall system integration, compactness, and electrical connection reliability. Simultaneously, the modular integrated structure offers excellent versatility and plug-and-play performance, making it well-suited for various application scenarios such as wearable health monitoring, electronic skin, bionic robots, and intelligent interaction. This provides a reliable integrated technical solution for the industrialization and large-scale application of high-precision, intelligent, and long-lasting water immersion monitoring technology. Attached Figure Description

[0089] Figure 1 This is a flowchart illustrating the preparation process of the POF / Ag / Ni3(HITP)2 / Nb2C MXene wrinkled composite structure of the present invention.

[0090] Figure 2 The following are XPS spectra of the POF / Ag / Ni3(HITP)2 / Nb2C MXene wrinkled composite structure of the present invention: (a) is the high-resolution XPS spectrum of C 1s, (b) is the high-resolution XPS spectrum of O 1s, (c) is the high-resolution XPS spectrum of Ag 3d, (d) is the high-resolution XPS spectrum of Ni 2p, (e) is the high-resolution XPS spectrum of Nb 3d and Cl 2p, and (f) is the high-resolution XPS spectrum of N 1s.

[0091] Figure 3 This is a schematic diagram of the microstructure of the POF / Ag / Ni3(HITP)2 / Nb2C MXene wrinkled composite structure of the present invention;

[0092] Figure 4 This is a flowchart illustrating the fabrication process of the planar interdigitated sensitive electrode pair of the present invention.

[0093] Figure 5 This is a schematic diagram of the structure of the water immersion sensor of the present invention;

[0094] Figure 6 This is a 3D top view of the sensor module in the water immersion sensor of the present invention.

[0095] Figure 7 This is a 3D top view of the stacked module in the water immersion sensor of the present invention.

[0096] Figure 8 This is a 3D top view of the sensor module in the pressure sensing device of the present invention.

[0097] Figure 9 This is a 3D top view of the stacked module in the water immersion sensor of the present invention;

[0098] Figure 10 This is a schematic diagram illustrating the working principle of the present invention;

[0099] Figure 11 This is a schematic diagram illustrating the working process of the water immersion sensor of the present invention. Detailed Implementation

[0100] The following embodiments are further illustrations of the present invention and serve as explanations of the technical content of the present invention. However, the essence of the present invention is not limited to the embodiments described below. Those skilled in the art can and should know that any simple changes or substitutions based on the spirit of the present invention should fall within the protection scope claimed by the present invention.

[0101] Example 1

[0102] Combination Figure 1 As shown, a method for preparing a POF / Ag / Ni3(HITP)2 / Nb2C MXene wrinkled composite structure is described, with the following specific steps:

[0103] (1) Preparation of POF substrate: Take a clean Si substrate with a length of 2 cm and a width of 2 cm, and a POF heat shrink film with a length of 2.5 cm and a width of 2.5 cm; fix the POF heat shrink film on the Si substrate with high temperature tape, heat it to 200 ℃ with a hot air gun, blow for 8 s, the POF heat shrink film shrinks when heated, and stop heating when it is completely attached to the Si substrate to obtain the POF substrate based on the Si substrate.

[0104] (2) Preparation of Ag layer: A silver film is deposited on the surface of the POF substrate obtained in step (1) to obtain a POF / Ag composite layer based on Si substrate;

[0105] (3) Preparation of Ni3(HITP)2 layer: 2 mg of washed and dried Ni3(HITP)2 powder was dispersed in a mixed solvent composed of isopropanol and deionized water in a volume ratio of 1:1, and ultrasonically treated until uniformly dispersed to obtain Ni3(HITP)2 electrodeposition solution; using a platinum sheet as the positive electrode and the POF / Ag composite layer as the negative electrode, electrochemical deposition was performed in the Ni3(HITP)2 electrodeposition solution under constant voltage of 0.5~10 V to obtain a POF / Ag / Ni3(HITP)2 composite layer based on Si substrate;

[0106] (4) Nb2C MXene layer: 10 μL of MXene with a concentration of 2 mg·mL -1 The Nb2C MXene aqueous solution was heated at a rotation speed of 2500 r·min. -1 The spin coating was applied to the surface of the POF / Ag / Ni3(HITP)2 composite layer for 35 seconds to obtain a POF / Ag / Ni3(HITP)2 / Nb2C MXene composite structure based on a Si substrate.

[0107] (5) Preparation of POF / Ag / Ni3(HITP)2 / Nb2C MXene wrinkled composite structure: The POF / Ag / Ni3(HITP)2 / Nb2C MXene composite structure obtained in step (4) is peeled off from the Si substrate and placed in an oven at 100 ℃ for 20 min to cause thermal shrinkage and wrinkling, and finally the POF / Ag / Ni3(HITP)2 / Nb2C MXene wrinkled composite structure is obtained.

[0108] In the wrinkled composite structure prepared in this embodiment, the thickness of the POF substrate layer is 15 μm, and the overall structure exhibits a regular wavy wrinkled structure. The spacing between adjacent wrinkle peaks or valleys is 3 μm, and the height difference between the wrinkle peaks and valleys is 2.5 μm. The wrinkle gaps, the interior of the wrinkles, and the top of the wrinkles are all completely covered by the Ag / Ni3(HITP)2 / Nb2C MXene composite structure. Specifically, the Ag layer has a thickness of 15 μm, the Ni3(HITP)2 layer has a thickness of 0.05 μm, and the Nb2C MXene layer has a thickness of 0.04 μm.

[0109] like Figure 2 , Figure 3 As shown, in the Ag 3d spectrum, except for Ag... 0 Besides the main peaks (binding energies 368.2 eV and 374.2 eV), an oxidized Ag⁺ peak exists at 367.7 eV, confirming chemical bonding between Ag and adjacent layers. The POF substrate surface is rich in hydroxyl groups (O1s spectrum binding energy 530.2 eV), providing an interfacial basis for Ag-O bond formation with the Ag layer. In the Ni₃(HITP)₂ layer, the N 1s spectrum (binding energy 398.8 eV) indicates Ag-N bond formation with Ag⁺. In the Nb₂C MXene layer, the Cl 2p spectrum (binding energies 197.7 / 199.2 eV) indicates Ag-Cl bond formation with Ag⁺. The Ni₃(HITP)₂ layer contains Ni… 3+ (Ni 2p3 / 2 binding energy 855.0 eV) and Nb in the Nb2C MXene surface oxide layer 5+ (Nb 3d5 / 2 binding energy 206.75 eV) is linked by Ni-O-Nb bonds formed through shared lattice oxygen (O 1s spectrum binding energy 528.7 eV); Ni³⁺ simultaneously forms Ni-OC bonds with hydroxyl groups on the POF substrate surface; Nb 5 ⁺ Forms Nb-OC bonds with the hydroxyl groups and carbon skeleton on the POF substrate surface. Adjacent layers are synergistically bonded through the above chemical bonds and π-π stacking between aromatic skeletons, resulting in tight interlayer bonding without delamination and excellent structural stability.

[0110] Example 2

[0111] Combination Figure 4 As shown, a planar interdigitated sensitive electrode pair and its fabrication are prepared in the same manner as in Example 1, except that a photolithography patterning step is added before the Ag layer is prepared in step (2). The specific operation is as follows:

[0112] Positive photoresist was uniformly spin-coated onto the surface of the POF substrate layer prepared in step (1), and then pre-baked at 85 ℃ for 5 min. After the interdigitated electrode pattern was exposed and transferred by the photolithography machine, the substrate was placed in the developer for 30 s to remove excess photoresist. After being thoroughly cleaned with deionized water, it was post-baked at 75 ℃ for 5 min to dry and solidify the photoresist layer and complete the interdigitated electrode pattern.

[0113] After the photolithography pattern is completed, the following steps are performed in sequence: Ag layer deposition, Ni3(HITP)2 layer electrodeposition, Nb2CMXene layer spin coating, and heat shrinking and wrinkling forming. Finally, the prepared device is immersed in NMP solution for desizing to remove residual photoresist and obtain the target planar interdigitated sensitive electrode pair.

[0114] The planar interdigitated sensing electrode pair prepared in this embodiment includes a set of symmetrical interdigitated electrodes. The electrode ends are provided with two pads, Pad1 and Pad2, for electrical lead-out. Before the heat-shrinking and wrinkling process, the linewidth of the interdigitated electrodes is 10–30 μm, and the line spacing is 100–250 μm. After the high-temperature heat-shrinking process, the electrodes shrink as a whole, ultimately reducing the linewidth to 5–15 μm and the line spacing to 55–150 μm. This micro / nano electrode structure effectively improves sensing sensitivity.

[0115] Example 3

[0116] This embodiment provides a water immersion sensor, combined with Figure 5 , Figure 6 , Figure 7 , Figure 8 , Figure 9 As shown, the device is mainly composed of a base 104, a sensing module 101, a stacking module 102, and a USB power supply module 103. The stacking module 102 is arranged from top to bottom as follows: a storage module 201, a data signal processing module 202, a microprocessor module 203, an acquisition module 204, a power management module 205, and a substrate 206. The USB power supply module 103 is located on the side of the base 104. All modules are solidified and assembled on the surface of the base 104 to form an integrated package structure.

[0117] like Figure 5 As shown, the left side of the water immersion sensor base 104 is hollowed out, and the sensing module 101 is placed in the hollowed-out area of ​​the base. The right side surface is integrated with solder pads and pins that correspond one-to-one with the stacked module 102, and provides a stable mounting position and physical support for the USB power supply module 103.

[0118] like Figure 6As shown, the sensing module 101 is assembled from a cover plate 301, a planar interdigitated sensitive electrode pair 302, a PAM hydrogel 303, a lead frame 304, and a base 305, and is a water immersion sensing unit.

[0119] The pin configurations for each functional module are as follows (it should be noted that the "I, II, III, IV, V, VI" serial numbers and "upper" and "lower" orientations used in the pin names in this manual are only for distinguishing pins of different functional modules, different mounting levels, and different electrical definitions, and have no special meaning. The entire text will use this rule to uniformly distinguish pins, and will not be repeated hereafter):

[0120] The sensing module 101 has a positive electrode and a negative electrode, for a total of two pins;

[0121] The storage module 201 has a total of 8 pins: power supply 1, ground 1, debug input 1, debug output 1, data input 1, data output 1, reset 1, and clock 1.

[0122] The data signal processing module 202 has eight pins: power supply pin 2, ground pin 2, debug input pin 2, debug output pin 2, data input pin 2, data output pin 2, reset pin 2, and clock pin 2.

[0123] The microprocessor module 203 has a total of 8 pins: power supply pin 3, ground pin 3, debug input pin 3, debug output pin 3, data input pin 3, data output pin 3, reset pin 3, and clock pin 3.

[0124] The acquisition module 204 has 8 pins: power supply, ground, debug input, debug output, data input, data output, reset, and clock.

[0125] The power management module 205 has 10 pins: power supply 5, ground 5, data reception positive 1, data reception negative 1, debug input 5, debug output 5, data input 5, data output 5, reset 5, and clock 5.

[0126] The substrate 206 is provided with 20 pins: power supply, ground, positive, negative, data receive positive, data receive negative, debug input 5, debug output 5, debug input 4, debug output 4, debug input 3, debug output 3, debug input 2, debug output 2, debug input 1, debug output 1, data input, data output, reset, and clock.

[0127] The USB power supply module 103 has four pins: power supply six, ground six, data reception positive two, and data reception negative two.

[0128] Each module is electrically interconnected on the base using a combination of chip side routing, flip-chip bonding with solder balls, copper-filled Si vias (433), and PI-printed copper conductors. The specific connection relationships are as follows:

[0129] Between storage module 201 and data signal processing module 202: Power supply 501 and ground 502 of storage module 201 are electrically connected to power supply 509 and ground 510 of data signal processing module 202 via side traces; reset pin 507 and clock pin 508 of storage module 201 are flip-chip bonded to reset pin 403 and clock pin 404 of data signal processing module 202 via solder balls; data input pin 505 and data output pin 506 of storage module 201 are respectively connected to… The data input 401 and data output 402 of the data signal processing module 202 are electrically connected; the debug input 503 and debug output 504 of the storage module 201 pass through the data signal processing module 202, the microprocessor module 203, the acquisition module 204 and the power management module 205 in sequence via copper-filled Si vias 433, and are connected to the debug input 427 and debug output 428 of the substrate 206 by flip-chip bonding with tin solder balls and board copper traces.

[0130] Between the data signal processing module 202 and the microprocessor module 203: Power supply pin 509 and ground pin 510 of the data signal processing module 202 are electrically connected to power supply pin 517 and ground pin 518 of the microprocessor module 203 via side traces; Reset pin 515 and clock pin 516 of the data signal processing module 202 are flip-chip bonded to reset pin 407 and clock pin 408 of the microprocessor module 203 via solder balls; Data input pin 513 and data output pin 514 of the data signal processing module 202... The second lower 514 is electrically connected to the data input third upper 405 and data output third upper 406 of the microprocessor module 203 respectively; the debugging input second lower 511 and debugging output second lower 512 of the data signal processing module 202 pass through the microprocessor module 203, the acquisition module 204 and the power management module 205 in sequence via copper-filled Si vias 433, and are connected to the debugging input second upper 425 and debugging output second upper 426 pins of the substrate 206 by flip-chip bonding with tin solder balls and board copper traces;

[0131] Microprocessor module 203 and acquisition module 204 Between: The power supply pin 517 and ground pin 518 of the microprocessor module 203 are electrically connected to the power supply pin 525 and ground pin 526 of the acquisition module 204 via side traces on the chip; the reset pin 523 and clock pin 524 of the microprocessor module 203 are flip-chip bonded to the reset pin 411 and clock pin 412 of the acquisition module 204 via solder balls; the data input pin 521 and data output pin 522 of the microprocessor module 203 are electrically connected to the data input pin 409 and data output pin 410 of the acquisition module 204, respectively; the debug input pin 519 and debug output pin 520 of the microprocessor module 203 pass through the acquisition module 204 and the power management module 205 sequentially via copper-filled Si vias 433, and are connected to the debug input pin 423 and debug output pin 424 of the substrate 206 via solder balls and copper traces.

[0132] Acquisition module 204 and power management module 205 Between: The power supply pin 525 and ground pin 526 of the acquisition module 204 are electrically connected to the power supply pin 533 and ground pin 534 of the power management module 205 via side traces on the chip; the reset pin 531 and clock pin 532 of the acquisition module 204 are flip-chip bonded to the reset pin 415 and clock pin 416 of the power management module 205 via solder balls; the data input pin 529 and data output pin 530 of the acquisition module 204 are electrically connected to the data input pin 413 and data output pin 414 of the power management module 205, respectively; the debug input pin 527 and debug output pin 528 of the acquisition module 204 pass through the power management module 205 via copper-filled Si vias 433 and are connected to the debug input pin 421 and debug output pin 422 of the substrate 206 via solder balls and copper traces.

[0133] Power management module 205 and baseboard 206 Between: Power management module 205's power supply pin 533 and ground pin 534 are electrically connected to substrate 206's power supply pin 543 and ground pin 544 via chip side traces; power management module 205's reset pin 541 and clock pin 542 are flip-chip bonded to substrate 206's reset pin 431 and clock pin 432 via solder ball flip bonding; power management module 205's data input pin 539 and data output pin 540 are electrically connected to substrate 206's data input pin 429 and data output pin 430 respectively; power management module 205's data receiving positive pin b535, data receiving negative pin b536, debug input pin 537, and debug output pin 538 are flip-chip bonded to substrate 206's data receiving positive pin a417, data receiving negative pin a418, debug input pin 419, and debug output pin 420 via solder ball flip bonding combined with board copper traces.

[0134] Between the sensing module 101 and the substrate 206: the positive terminal 1 and negative terminal 1 of the sensing module 101 are electrically connected to the corresponding positive terminal 545 and negative terminal 546 of the substrate 206 via copper wires printed with PI adhesive.

[0135] Between the USB power supply module 103 and the substrate 206: the power supply six, ground six, data receiving positive two, and data receiving negative two pins of the USB power supply module 103 are electrically connected to the power supply 543, ground 544, data receiving positive 547, and data receiving negative 548 pins of the substrate 206 via copper wires printed with PI adhesive.

[0136] Between substrate 206 and base 104: power supply 543, ground 544, positive terminal down 545, negative terminal down 546, data receive positive 547, data receive negative 548, debug input down 549, debug output down 550, debug input down 451, debug output down 452, debug input down 353, debug output down 354, debug input down 255, debug output down 256, debug input down 1557, debug output down 1558, data input down 559, data output down 560, reset down 561, clock down 562, are connected to the corresponding pad pins of base 104 one by one through solder balls;

[0137] After all functional modules are assembled, polyimide sealing material is used to fill all gaps between the modules, forming an integrated sealed encapsulation shell. The flip-chip bonding structure used for electrical interconnection consists of tin solder balls with a diameter controlled between 200 μm and 400 μm; the vertical conduction structure uses copper-filled Si vias with a via diameter of 10 μm to 50 μm, filled with high-purity copper. The overall encapsulation structure is dense and cavity-free, effectively ensuring the stability of the electrical connections and the reliability of the mechanical structure of the entire device.

[0138] Example 4

[0139] Combination Figure 10 , 11 As shown, a water immersion detection method using a water immersion sensor is described, and the specific steps of this method are as follows:

[0140] (1) Power-on initialization of the device: After the water immersion sensor is powered on, it automatically completes system initialization, performs baseline calibration on the sensing module, and obtains the initial capacitance value C0 of the sensor in the state of no solution contact.

[0141] (2) Sensing signal response: When the external aqueous solution comes into contact with the hollow sensing area of ​​the sensing module, the solution quickly penetrates into the internal PAM hydrogel layer, causing the PAM hydrogel to absorb water and swell and expand in volume; the squeezing force generated by the swelling continues to act on the sensing area of ​​the planar interdigitated electrode, causing regular changes in the distance between the interdigitated electrodes and the electrode contact state, and finally realizing the dynamic change of the capacitance value between the electrodes.

[0142] (3) Signal acquisition and transmission: The acquisition module acquires the analog signal of capacitance change output by the sensing module in real time and transmits the acquired electrical signal to the data signal processing module in real time;

[0143] (4) Data processing and output: The data signal processing module performs smoothing filtering and noise reduction on the acquired transient capacitance response signal to remove environmental noise and baseline interference; the solution adsorption amount is calculated according to the linear fitting formula C=0.58ΔV+C0; where C is the real-time capacitance value in pF; ΔV is the solution addition amount in μL; and C0 is the initial capacitance value.

[0144] Ultimately, depending on the operating mode, the processed absorption solution volume data is stored in the storage module or transmitted to an external pin output.

[0145] The water immersion sensor of this invention can be widely used in wearable health monitoring, electronic skin, bionic robots, intelligent interactive devices and other fields. It can accurately detect the amount of solution contact, sweat secretion, body fluid leakage and wetness of the contact surface, and has the advantages of fast response, high sensitivity, good stability and long-term cyclic use.

[0146] It should be noted that the above embodiments of the present invention are merely illustrative examples provided to enable those skilled in the art to understand the technical essence of the present invention. Any modifications, equivalent substitutions, and improvements made based on the essential spirit of the present invention, particularly the described multiple chemical bond interface enhancement mechanism and heat-shrinkable wrinkle sensitizing structure, should be within the scope of protection of the present invention.

Claims

1. A POF / Ag / Ni3(HITP)2 / Nb2C MXene wrinkled composite structure, characterized in that, It includes a POF substrate, an Ag layer, a Ni3(HITP)2 layer and an Nb2C MXene layer stacked sequentially from bottom to top; The POF substrate and the Ag layer are connected by Ag-O bonds formed between the hydroxyl groups on the surface of the POF substrate and the silver atoms. The Ag layer and the Ni3(HITP)2 layer are connected by Ag-N bonds formed between silver atoms and nitrogen atoms in the Ni3(HITP)2 layer; The Ag layer and the Nb2C MXene layer are connected by Ag-Cl bonds formed between silver atoms and chlorine atoms doped in the Nb2C MXene layer. The connection between the Ni3(HITP)2 layer and the Nb2C MXene layer is achieved through Ni-O-Nb coordination bonds formed by nickel atoms in the Ni3(HITP)2 layer and niobium atoms in the Nb2C MXene layer on the surface oxide layer, as well as π–π bonds between the aromatic skeletons. The Ni3(HITP)2 layer and the POF substrate are connected by Ni-OC coordination bonds formed between the nickel atoms of the Ni3(HITP)2 layer and the hydroxyl groups on the surface of the POF substrate. The Nb2C MXene layer and the POF substrate are connected by Nb-OC coordination bonds formed by niobium atoms in the Nb2C MXene layer, the carbon skeleton of the POF substrate, and hydroxyl groups on the surface of the POF substrate.

2. The POF / Ag / Ni3(HITP)2 / Nb2C MXene wrinkled composite structure according to claim 1, characterized in that, The Ag-O bond length is 3.0~3.6 Å; the Ag-N bond length is 2.6~3.0 Å; the Ag-Cl bond length is 2.6~3.2 Å; the Ni-O-Nb coordination bond length is 2.2~3.8 Å; the Ni-OC coordination bond length is 2.3~3.0 Å; and the Nb-OC coordination bond length is 2.3~3.2 Å.

3. The POF / Ag / Ni3(HITP)2 / Nb2C MXene wrinkled composite structure according to claim 1, characterized in that, The thickness of the POF substrate is 3~25 μm, and the POF substrate has a wavy folded structure; the spacing between adjacent fold peaks or adjacent fold valleys is 0.5~5 μm, and the height difference between fold peaks and fold valleys is 1~5 μm; the gaps, interiors, and tops of the folds are all covered with an Ag / Ni3(HITP)2 / Nb2C MXene composite structure; the thickness of the Ag layer is 5~25 μm, the thickness of the Ni3(HITP)2 layer is 0.01~0.1 μm, and the thickness of the Nb2C MXene layer is 0.01~0.1 μm.

4. A method for preparing the POF / Ag / Ni3(HITP)2 / Nb2C MXene wrinkled composite structure according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Fix the POF heat shrink film on a clean substrate and heat it for 8 to 10 seconds at 150 to 250 °C using a hot air gun so that the POF heat shrink film shrinks and completely adheres to the substrate, thus obtaining the POF base layer loaded on the substrate. (2) A silver film was deposited on the surface of the POF substrate using a vacuum deposition process to obtain a POF / Ag composite layer; (3) Take 1~5 mg of washed and dried Ni3(HITP)2 powder, disperse it in a mixed solvent composed of isopropanol and deionized water, and sonicate it until it is uniformly dispersed to obtain Ni3(HITP)2 electrodeposition solution; use a platinum sheet as the positive electrode and the POF / Ag composite layer obtained in step (2) as the negative electrode, and perform electrodeposition under a constant voltage of 0.5~10 V to obtain POF / Ag / Ni3(HITP)2 composite layer; (4) Take 1~20 μL of solution with a concentration of 2 mg·mL -1 An aqueous solution of Nb2C MXene was dropped onto the surface of a POF / Ag / Ni3(HITP)2 composite layer at a rate of 2000–3000 r·min. -1 Spin coating was performed at a rotation speed of 20~45 s to obtain a POF / Ag / Ni3(HITP)2 / Nb2C MXene composite structure; (5) Peel the composite structure obtained in step (4) from the substrate and place it in an oven at 80~130 ℃ for 3~30 min. After heat shrinking deformation, a wrinkled composite structure is formed.

5. A planar interdigitated sensitive electrode pair based on the pleated composite structure described in any one of claims 1-3, characterized in that, It includes a pair of interdigital electrodes and pads respectively disposed at the ends of the interdigital electrodes; before heat shrinking, the linewidth of the interdigital electrodes is 10~30 μm and the line spacing is 100~250 μm; after heat shrinking, the linewidth of the interdigital electrodes is 5~15 μm and the line spacing is 55~150 μm.

6. A method for preparing the planar interdigitated sensitive electrode pair according to claim 5, characterized in that, After the POF substrate is prepared according to step (1) of claim 4 and before step (2), a photolithography patterning step is also included: Positive photoresist was spin-coated onto the POF substrate surface, followed by pre-baking at 82-87 ℃ for 4-6 min, pattern transfer via photolithography, development with developer for 25-35 s, rinsing with deionized water, and post-baking at 72-78 ℃ for 4-6 min. After completing the photolithography pattern, perform steps (2) to (5) as described in claim 4, and finally immerse the product in NMP solution for degumming treatment to obtain the planar interdigitated sensitive electrode pair.

7. A sensing module, characterized in that, The device includes, from bottom to top, a base, PAM hydrogel, interdigitated electrode pairs, lead frame, and cover plate, wherein the interdigitated electrode pairs are the planar interdigitated sensitive electrode pairs as described in claim 5 or the planar interdigitated sensitive electrode pairs prepared by the preparation method described in claim 6. The base has a hollow structure, and the PAM hydrogel fills the hollow structure; The planar interdigitated sensitive electrode pair is fixedly installed on the base, with the interdigitated area of ​​the planar interdigitated sensitive electrode pair facing the hollow structure and in contact with the PAM hydrogel; The lead frame is fixed to the planar interdigitated sensitive electrode pair, and the pins of the lead frame extend to the slot of the base. The cover plate is fastened to the top of the lead frame. The cover plate and the base are positioned and prevented from shifting by interlocking with the groove and the slot. The cover plate has a through hole, which is directly opposite the sensing area of ​​the sensitive membrane of the planar interdigitated sensitive electrode pair.

8. A method for packaging the sensing module according to claim 7, characterized in that, Includes the following steps: (1) Use DAF adhesive to bond and fix the planar interdigitated sensitive electrode pair to the base, so that the interdigitated area is aligned with the hollow structure of the base; the pads of the planar interdigitated sensitive electrode pair are electrically connected to the lead frame through conductive silver paste, conductive adhesive or carbon cloth. (2) Fill the hollow structure of the base with PAM hydrogel so that the PAM hydrogel is in full contact with the planar interdigitated sensitive electrode pair; (3) Apply sealant to the joint between the cover plate and the base. The sealant is epoxy resin or silicone rubber and is cured at room temperature for 16-32 hours. (4) Inject sealing material into the potting mold until the sealing material completely covers the cover plate, and cure again at room temperature for 16~32 h to complete the overall encapsulation.

9. A water immersion sensor, characterized in that, It includes a substrate, a USB power supply module, a power management module, a microprocessor module, a data acquisition module, a data signal processing module, a storage module, a base, and a sensing module as described in claim 7 or a sensing module obtained by the packaging method described in claim 8. The sensing module is used to sense the external solution and convert the pressure signal generated by swelling into an electrical signal. The acquisition module is electrically connected to the sensing module and is used to acquire the electrical signals output by the sensing module. The data signal processing module has a built-in AD conversion unit and a data processing unit. The data signal processing module is electrically connected to the acquisition module and is used to convert the acquired analog electrical signals into digital signals and complete data processing. The storage module is electrically connected to the data signal processing module and is used to store the detection data processed by the data signal processing module. The microprocessor module is electrically connected to the acquisition module, data signal processing module, storage module and power management module respectively, and is used to issue control commands to each module and coordinate the working status of each module; The USB power supply module is electrically connected to the power management module, which provides power to the sensing module, acquisition module, data signal processing module, storage module, and microprocessor module respectively. The base is used to support and fix the substrate and various functional modules. Through its internal integrated circuit layout, mechanical connection and electrical conduction between the modules are realized. The functional modules are electrically connected on the base through tin solder balls, copper-filled Si vias, and PI adhesive printed copper wires. The gaps between the modules are filled with polyimide to form an overall package shell.

10. An application of a sensing module based on the sensing module of claim 7 or the packaging method of claim 8, or the water immersion sensor of claim 9, in a pressure sensing device, characterized in that, The pressure sensing devices include wearable health monitoring devices, electronic skin, bionic robots, and intelligent interactive devices. The pressure sensing device can achieve pressure sensing and detection, specifically including the following steps: (1) Power on the device and initialize it to obtain the initial capacitance value C0 of the sensing module; (2) When the external solution comes into contact with the sensing module, the solution seeps into the PAM hydrogel and causes it to absorb water and swell. The squeezing force generated by the swelling acts on the planar interdigitated sensitive electrode pair, causing the capacitance between the electrodes to change. (3) The acquisition module acquires the capacitance signal in real time and transmits it to the data signal processing module. The data signal processing module performs noise reduction and smoothing processing on the signal according to the formula C=0.58△V+C0; where C is the real-time capacitance value in pF; △V is the amount of solution added in μL; and C0 is the initial capacitance value of the device. (4) Depending on the working mode, the calculated amount of solution added is stored in the storage module or output to the outside through the external pin.

Images