An electrostatic flexible pressure sensor with nano-crown platform structure and a preparation method thereof

Abstract

The application discloses a flexible capacitive pressure sensor with a nano-crown platform structure and a preparation method thereof. The sensor is a layered structure, and comprises an upper electrode, a lower electrode and an ionic gel layer arranged between the upper electrode and the lower electrode, and can further comprise a PDMS frame-shaped intermediate layer arranged between the ionic gel layer and the lower electrode. The ionic gel layer is formed by compounding PVDF-HFP and ionic liquid, and the surface of the ionic gel layer has a nano-crown platform structure obtained by replication molding with a patterned sapphire substrate template; and the surface has a corresponding inverse pit structure. The PDMS frame-shaped intermediate layer can be used for defining an effective sensing area and reducing the initial capacitance of the device, so as to improve the signal readability and assembly stability of the device in the pressure detection process. The sensor preparation process is simple, the template can be repeatedly used, and the microstructure molding consistency is good.

Description

Technical Field

[0002] This invention relates to the field of flexible pressure sensor technology, and in particular to an ionized flexible pressure sensor with a nano-crown structure and its fabrication method. Background Technology

[0003] Flexible pressure sensors, as fundamental components of flexible electronics, electronic skin, and human-computer interaction, have been widely applied in fields such as robotic tactile sensing, wearable health monitoring, and intelligent interactive input. Existing flexible pressure sensors, based on their working mechanisms, typically include piezoresistive, piezoelectric, and capacitive types. Among them, traditional dielectric-capacitive sensors achieve pressure detection through changes in dielectric layer thickness or dielectric constant, offering advantages such as simple structure and low power consumption. However, in detecting minute pressure signals, they are often limited by the low capacitance density of the dielectric layer, resulting in limited amplitude of output signal changes.

[0004] Ionized pressure sensors utilize a charge-separated double-layer structure formed at the interface between electrodes and ionic media (ionic liquids, ionic gels, etc.). Their equivalent capacitance density can be significantly higher than that of traditional dielectric capacitors, thus improving signal response under minute pressures. These sensors typically generate measurable capacitance changes by altering the contact state at the electrode-ionic medium interface caused by external pressure, leading to changes in the effective contact area of ​​the double layer or the interface charge distribution. Due to their high interface capacitance density and good flexibility, ionized pressure sensors have attracted attention in low-pressure tactile sensing and wearable applications.

[0005] To further improve the sensitivity and usability of ionized pressure sensors, existing technologies often introduce microstructures (such as micropillars, microdots, and micropores) onto the electrode or ion-medium surface to amplify the effective contact area change under pressure, thereby increasing the capacitance change. However, existing microstructure designs are mostly micrometer-scale, and micrometer-scale structures have limited modulation of the interface contact state under lower pressures, making it difficult to fully utilize the advantages of ionized sensing in low-pressure regions. Furthermore, at higher pressure ranges, contact saturation or enhanced nonlinearity can easily occur, making it difficult to simultaneously achieve optimal sensitivity, range, and linearity.

[0006] Theoretically, further reducing the feature size of microstructures to the nanoscale could potentially trigger more significant interfacial contact changes under lower pressures, thereby achieving higher low-pressure response capabilities. Existing nanostructured ionogel pressure sensors are typically fabricated using micro / nano fabrication templates, nanoimprint templates, or porous anodic alumina templates. While porous anodic alumina templates can provide nanoscale structures, they usually require removal after molding via acid-base etching, making template reuse difficult. Furthermore, the chemical removal process can increase process complexity and affect the integrity of the ionogel structure. On the other hand, existing sapphire template solutions are mostly used to construct micrometer-scale surface structures, but their feature sizes are relatively large, and their ability to modulate changes in interfacial contact area in low-pressure regions still has room for improvement. Therefore, how to utilize reusable rigid templates to form regular nanoarray structures on the ionogel surface using a non-sacrificial demolding method remains a valuable area for improvement.

[0007] Furthermore, the initial capacitance of an ion-type capacitive sensor is closely related to its assembly and bonding state. If the initial capacitance of the device is too large or the initial capacitance varies significantly between samples, it will negatively impact the readability and consistency of the output signal. Simultaneously, flexible devices may experience bonding errors, edge compression, and inconsistent effective areas during assembly and packaging, which will also affect the sensor's stability and repeatability. Therefore, while ensuring high sensitivity, improving device consistency and engineering feasibility through structural design and assembly methods is a crucial technical challenge that needs to be addressed.

[0008] In summary, there is an urgent need to provide an ionized flexible pressure sensor and its fabrication method, which can construct a regular nanoarray structure on the surface of an ion gel in a non-sacrificial peeling and demolding manner, and has the advantages of washable and reusable templates, simple demolding process, and good replication consistency, thereby improving pressure detection capability and meeting the needs of robotic tactile and wearable applications. Summary of the Invention

[0009] The purpose of this invention is to overcome the problems commonly found in existing ionized flexible pressure sensors, such as large microstructure scale, high cost and complex manufacturing process for nanostructures, difficulty in reusing templates, and insufficient replication consistency. This invention provides an ionized flexible pressure sensor based on sapphire template replication to create nanoscale microstructures, along with its fabrication method and applications. This results in a flexible pressure sensing device that is simple to manufacture, low in cost, reproducible, and possesses high pressure response capability. To achieve the above objectives, this invention provides the following technical solution.

[0010] An ionized flexible pressure sensor with a nanocluster structure includes: An upper electrode, a lower electrode, and an ion gel layer sandwiched between the upper electrode and the lower electrode; The ionogel layer is formed by combining a polymer matrix and an ionic liquid to form an ionogel material, and at least one side surface of the ionogel layer has an array of nano-crown protrusions. The nano-crown protrusion array is obtained by directly pouring ion gel precursor liquid into the surface pit structure of a patterned sapphire substrate PSS hard template and curing it, and then replicating it by a non-sacrificial peeling demolding method. The PSS hard template is a single crystal sapphire substrate with a periodically arranged inverted pit structure pre-formed on its surface. The PSS hard template retains structural integrity after demolding and can be reused for the next replication after cleaning. When external pressure is applied to the sensor, the effective contact area of ​​the double layer between the electrode surfaces of the upper and / or lower electrodes and the nano-crown protrusion array on the surface of the ion gel layer changes with the pressure, causing a change in the interfacial double layer capacitance, thereby achieving pressure detection.

[0011] Preferably, the polymer matrix is ​​polyvinylidene fluoride-hexafluoropropylene copolymer PVDF-HFP, and the ionic liquid is selected from imidazole bis(trifluoromethanesulfonyl)imine salts; In the ionogel layer, the mass ratio of polymer matrix to ionic liquid enables the ionogel to form a flexible cross-linked network with peelable self-supporting properties, and the thickness of the ionogel layer is 0.3–0.8 mm.

[0012] Preferably, each crown of the nano-crown protrusion array has a top platform region, inclined sidewalls, and a bottom transition rounded corner region, and has a polygonal outline in the top-view projection direction; the crown height is 200–260 nm, the lateral equivalent radius of the crown structure is 150–350 nm, and the center-to-center distance between adjacent crowns is 0.8–1.2 μm.

[0013] Preferably, the upper electrode and the lower electrode are planar structure electrodes; the upper electrode and the ion gel layer and the lower electrode and the ion gel layer form an electrode-ion gel interface by direct attachment; the nano-crown protrusion array is arranged toward the planar structure electrode, so that effective double-layer contact mainly occurs in the top platform region of the crown under low pressure, and gradually extends to the inclined sidewall region as the pressure increases.

[0014] Preferably, the frame-shaped intermediate interlayer is disposed between the ionogel layer and the lower electrode or between the upper electrode and the ionogel layer; The frame-shaped interlayer is a hollow frame structure, with an effective sensing window area defined inside the frame. The thickness of the frame itself is in the range of 100–300 μm, and the frame-shaped interlayer is made of PDMS material. The frame-shaped intermediate interlayer constrains the effective double-layer contact between the ion gel layer and the electrode within the windowed area, thereby reducing the initial capacitance under no-pressure conditions and improving the assembly consistency between devices.

[0015] Preferably, the interface between the ion gel layer and the electrode is subjected to plasma treatment before assembly to increase the surface energy; the sensor also includes a flexible encapsulation layer covering the outer surface of the layered structure composed of the upper electrode, the lower electrode, and the ion gel layer, wherein the encapsulation layer is made of PI and has a thickness in the range of 0.05–0.15 mm.

[0016] Preferably, the PSS rigid template is a commercially available patterned sapphire substrate wafer, whose surface inverted pit structure was originally used as a patterned substrate for LED epitaxial growth. The pits have an aperture of 300–700 nm, a depth of 200–260 nm, and a center-to-center spacing of 0.8–1.2 μm. The ion gel precursor liquid is filled into the pits and cured at 80–120 °C. The gel is then demolded from the PSS rigid template surface by mechanical peeling. After demolding, the surface of the ion gel is left with an array of nano-crown protrusions that are complementary to the pits.

[0017] The method for manufacturing the ionized flexible pressure sensor includes the following steps: S1. Preparation of ionogel precursor solution: Dissolve PVDF-HFP in DMF solvent, heat and stir until completely dissolved, add ionic liquid and continue stirring, then sonicate to obtain homogeneous ionogel precursor solution; S2. Take a commercially available PSS rigid template, clean and dry its surface, add the ion gel precursor liquid to the template surface and fill the reverse pit array on the template surface with the precursor liquid, and cure it at 75–120℃ for 2–6 h to allow the solvent to evaporate and the ion gel network to form. S3. Mechanically peel off the solidified ionogel layer from the edge of the PSS template to obtain a flexible ionogel layer with a nano-crown protrusion array on the surface. S4. The upper electrode and the lower electrode are respectively attached to the upper and lower sides of the ion gel layer to form a layered sandwich sensing structure. Plasma treatment is performed to improve the interface adhesion, and then flexible encapsulation is performed to obtain the ionized flexible pressure sensor. S5. After the PSS rigid template is demolded, it is solvent cleaned and / or ultrasonically cleaned, dried, and then returned to step S2 for reuse.

[0018] Preferably, in step S1, the mass ratio of PVDF-HFP:DMF solvent:ionic liquid is 1:(4–7):(2–4); In step S2, the curing temperature is 80±5℃ and the curing time is ≥4 h; In step S3, the demolding method is purely mechanical peeling along the edge of the template, without involving acid or alkali corrosion to remove the template; In step S4, the bonding surface of the ionogel layer and / or the electrode surface are subjected to argon or oxygen plasma treatment for 60–180 s before bonding.

[0019] Preferably, the preparation method further includes: Preparation of PDMS frame-shaped gaskets; A PDMS frame-shaped pad is placed between the ionogel layer and the lower electrode, so that the opening area of ​​the frame-shaped pad corresponds to the effective sensing area. The lower electrode, ion gel, and upper electrode are bonded together within the opening area of ​​the frame-shaped gasket.

[0020] In a preferred embodiment, the template is a patterned sapphire substrate template, abbreviated as PSS template, where PSS stands for Patterned Sapphire Substrate. The PSS template is a single-crystal α-Al₂O₃ sapphire hard template with a surface pre-formed with inverted pit structures corresponding to the nanocrystal structure. The PSS template can be a commercially available 2-inch patterned sapphire substrate wafer, or a template sheet cut from such a 2-inch wafer. The PSS template can be used to replicate and form nanocrystal structures on the surface of ion gels without requiring photolithography, etching, or nanoimprinting to prepare the template. The PSS template is not chemically etched away during the ion gel curing and demolding process, retains its structural integrity after demolding, and can be reused after cleaning and drying.

[0021] In a preferred embodiment, the ionogel layer may be subjected to plasma treatment before being bonded to the electrode to improve bonding stability, preferably argon plasma treatment, and the treatment time is preferably 120 s.

[0022] In a preferred embodiment, an encapsulation layer is provided on the outside of the sensor for sealing protection, preferably a PI encapsulation layer for full coverage encapsulation; preferably, the thickness of the PI encapsulation layer is about 0.1 mm to improve the environmental adaptability and stability of the device in wearable, tactile interaction and other scenarios.

[0023] The present invention also provides a method for fabricating the ionized flexible pressure sensor as described above, comprising: preparing an ion gel precursor solution; introducing the ion gel precursor solution into a sapphire template and curing it; demolding to obtain an ion gel layer with a nano-crown structure; bonding the ion gel layer to upper and lower electrodes to form a layered structure; optionally setting a PDMS frame-shaped intermediate layer; and encapsulating the device to obtain the finished sensor.

[0024] In some embodiments, the preparation method of the PDMS frame-shaped intermediate interlayer includes: mixing the PDMS main agent and the curing agent in a ratio of 10:1 and stirring for 3–5 min; degassing the mixed solution under vacuum for about 30 min; pouring the degassed PDMS solution into a PMMA plate with a frame-shaped cavity; curing at 80 °C for about 2 h; and demolding to obtain a PDMS frame-shaped gasket.

[0025] The sensor of this invention operates based on the electric double-layer capacitance (EDL) mechanism. Migratable ions exist within the ionogel layer. When the upper electrode and the lower electrode contact the ionogel layer, a charge separation layer, i.e., an electric double-layer structure, is formed at the electrode-ionogel interface. This interface can be equivalent to a capacitor unit, and its equivalent capacitance is positively correlated with the effective contact area of ​​the interface.

[0026] Under external pressure, the adhesion between the electrode and the ionogel layer increases. Simultaneously, due to the nanoarray microstructure on the ionogel surface, the interfacial micro-contact evolves from initial local contact to more complete surface contact, leading to a significant change in the effective contact area of ​​the double layer and consequently, a change in the equivalent capacitance. Compared to micrometer-scale structures, nanoarrays have smaller feature scales and higher interfacial curvature, allowing for more pronounced micro-contact evolution and area modulation even under lower pressure, thus improving the capacitive response in low-pressure regions.

[0027] In terms of measurement methods, an LCR meter can be used to read the device capacitance. To reduce the influence of the initial capacitance difference between samples and to facilitate comparison, the normalized capacitance change can be used as a characterization quantity. The normalized output is defined as ΔC / C0=(C-C0) / C0, where C0 is the initial capacitance without pressure and C is the capacitance after pressure is applied.

[0028] In an optional embodiment, by setting a PDMS frame-shaped intermediate interlayer between the ionogel layer and the lower electrode, the effective sensing area can be defined and the initial effective contact area can be reduced, thereby reducing the initial capacitance of the device and improving the readability of the output signal and assembly consistency. This structure does not change the basic mechanism of EDL, but rather optimizes the initial state and effective area of ​​the device through engineering.

[0029] Compared with the prior art, the present invention has at least the following beneficial effects: (1) The nano-crown microstructure is replicated using a sapphire (PSS) template, which makes the effective contact area of ​​the electrode-ion gel interface more significantly modulated during the pressure process, thereby improving the pressure response capability; (2) The sapphire template is a commercially available template with advantages such as low cost, reusability, and easy demolding, which is conducive to improving the consistency of microstructure replication and reducing manufacturing costs; (3) The optional PDMS frame-shaped intermediate layer can be used to define the effective sensing area and adjust the initial contact state, which is conducive to reducing the initial capacitance fluctuation and improving the assembly consistency and signal readability; (4) Combined with plasma processing and PI full-coverage packaging, it can improve the device bonding stability and environmental adaptability, and is suitable for robot tactile and wearable applications. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the embodiments of the present invention are briefly described below. It should be understood that the following drawings are for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0031] Figure 1 This is a schematic diagram of the structure of the ionized flexible pressure sensor of the present invention; Figure 2(A) is a SEM image of the PSS template surface; Figure 2(B) shows the three-dimensional AFM morphology of the PSS template surface. Figure 2(C) is a cross-sectional profile of a single inverted pit structure on the surface of the PSS template; Figure 3 The image shows the morphology of the nanocranial structure on the surface of the ion gel obtained by replication using a PSS template. Figure 4 The pressure-capacitance response curves of the nanostructured ionogel sensor and the unstructured ionogel sensor are compared under the same test conditions. Figure 5 This is a schematic diagram of the PDMS frame-shaped intermediate layer structure.

[0032] Figure descriptions: 1—Upper electrode; 2—Ion gel layer; 21—Nano-crown structure; 3—Lower electrode; 41—Upper encapsulation layer; 42—Lower encapsulation layer. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Equivalent modifications to materials, parameters, structures, and processes made by those skilled in the art without departing from the concept of the present invention should fall within the scope of protection of the present invention.

[0034] An ionized flexible pressure sensor includes an upper electrode, a lower electrode, and an ion gel layer disposed between the upper and lower electrodes. The ion gel layer is a polymer-ionic liquid composite ion gel. At least one side of the ion gel layer has a nano-crown structure, which is formed by casting, curing, and demolding a patterned sapphire substrate template with corresponding inverted pit structures on its surface. The patterned sapphire substrate template is a single-crystal sapphire hard template that is not chemically etched away during demolding and can be repeatedly used to replicate the nano-crown structure on the ion gel surface. When external pressure is applied to the sensor, the effective contact area of ​​the electric double layer at the interface between the electrode and the ion gel layer changes, thereby causing a change in capacitance to achieve pressure detection. The polymer is polyvinylidene fluoride-hexafluoropropylene copolymer PVDF-HFP. The ion liquid includes 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIM-TFSI). The ion gel is prepared by mixing PVDF-HFP, DMF, and EMIM-TFSI in a mass ratio of 1:5:3. The nano-crown structure has a top platform region, inclined sidewalls, and a bottom transition region. The nano-crown structure has a polygonal outline when viewed from above. The thickness of the ionogel layer is 0.3–0.8 mm, preferably about 0.5 mm.

[0035] The nano-crown structure is a nanoscale protrusion formed by reverse replication from a patterned sapphire substrate template. It has a top platform region, sloping sidewalls, and a bottom transition region. Preferably, the height of the nano-crown structure is 200–260 nm, and the lateral equivalent radius is 150–350 nm, more preferably 200–280 nm. The center-to-center distance between adjacent nano-crown structures is 0.8–1.2 μm. This nano-crown structure allows for a more significant change in interfacial contact area under relatively low pressure, thereby enhancing the double-layer capacitance modulation effect.

[0036] The upper and / or lower electrodes are conductive copper tape electrodes with a planar structure. Before bonding the ionogel layer to the electrodes, at least one bonding surface undergoes plasma treatment, preferably argon plasma treatment for 120 s. The sensor is fully encapsulated and sealed using a PI encapsulation layer, preferably with a thickness of approximately 0.1 mm. A PDMS frame-shaped intermediate interlayer is also included, disposed between the ionogel layer and the lower electrode. The PDMS frame-shaped intermediate interlayer is a frame-shaped gasket with an outer edge length of 1.2 cm and an inner edge length of 1.0 cm. The thickness of the PDMS frame-shaped intermediate interlayer is 100–300 μm, preferably approximately 150 μm. The PDMS frame-shaped intermediate interlayer is used to define the effective sensing area and reduce the initial capacitance of the sensor.

[0037] The patterned sapphire substrate template is a single-crystal α-Al₂O₃ sapphire hard template, which differs from porous anodic aluminum oxide sacrificial templates. The patterned sapphire substrate template is a commercially available patterned sapphire substrate wafer, i.e., a PSS wafer (Patterned Sapphire Substrate); preferably, the PSS wafer is a 2-inch wafer, or a template sheet cut from a 2-inch PSS wafer. The ionogel layer is obtained by demolding from the sapphire template using a peel-off method.

[0038] The method for fabricating the ionized flexible pressure sensor includes: 1. Mixing PVDF-HFP and DMF, and stirring under heating conditions to dissolve them; 2. Adding an ionic liquid and continuing to stir to obtain an ionized mixed solution; the mass ratio of PVDF-HFP, DMF and ionic liquid is 1:5:3; 3. Sonicating the ionized mixed solution; 4. Introducing the ionized mixed solution onto the surface of a sapphire template and curing it, then demolding to obtain an ion gel layer with a nano-crown structure array on the surface; 5. Bonding the upper electrode and the lower electrode to the ion gel layer to form a layered structure and encapsulating them to obtain the ionized flexible pressure sensor.

[0039] The curing temperature is 80℃, and the curing time is ≥4 h. After the ionogel layer is demolded, the sapphire template is cleaned and dried before being reused for the next replication molding. The cleaning includes solvent cleaning and / or ultrasonic cleaning. Before bonding, the ionogel layer and / or electrode surface are subjected to argon plasma treatment for 120 s.

[0040] The preparation method also includes preparing and setting a PDMS frame-shaped intermediate interlayer. The preparation of the PDMS frame-shaped intermediate interlayer includes: mixing the PDMS main agent and the curing agent at a ratio of 10:1 and stirring for 3–5 min, degassing under vacuum for about 30 min, pouring it into a PMMA plate with a frame-shaped cavity and curing at 80°C for about 2 h, and demolding to obtain the PDMS frame-shaped intermediate interlayer.

[0041] Example 1 This embodiment provides an ionized flexible pressure sensor, the structure of which is as follows: Figure 1 As shown, the structure includes an upper electrode, a lower electrode, and an ion gel layer located between them; the surface of the ion gel layer has a nano-crown structure replicated from a PSS template. The morphology of the nano-crown inverted pit structure on the PSS template surface is shown in Figures 2(A) to 2(C), and the SEM morphology of the nano-array on the ion gel surface is shown in... Figure 3 .

[0042] The surface of the ion gel layer has a nano-crown structure replicated from a patterned sapphire substrate template; the patterned sapphire substrate template is a single-crystal sapphire hard template with an inverted pit structure on its surface; when external pressure is applied to the sensor, the effective contact area of ​​the double layer at the interface between the electrode and the ion gel layer changes, thereby causing a change in capacitance to achieve pressure detection.

[0043] The upper and / or lower electrodes are conductive copper tape electrodes with a planar structure to facilitate bonding with the ion gel layer to form a stable electrode-ion gel interface.

[0044] In a preferred embodiment, the sensor further includes a PDMS frame-shaped intermediate layer disposed between the ionogel layer and the lower electrode; the PDMS frame-shaped intermediate layer is used to define the effective sensing area and reduce the initial capacitance of the device, thereby improving assembly consistency and output signal readability. Preferably, the PDMS frame-shaped intermediate layer is a frame-shaped gasket with an outer edge length of 1.2 cm, an inner edge length of 1.0 cm, and a thickness preferably about 150 μm.

[0045] 1. Weigh PVDF-HFP and DMF, mix them at a mass ratio of 1:5, place them on a magnetic stirrer, and stir at 600 r / min at 80℃ for 2 h to fully dissolve PVDF-HFP and obtain the first mixed solution.

[0046] 2: Add EMIM-TFSI to the first mixed solution to make the mass ratio of PVDF-HFP:DMF:EMIM-TFSI 1:5:3, and continue stirring at room temperature for 2 h to obtain an ion gel mixed solution.

[0047] 3: The ion gel mixture solution is sonicated for about 15 minutes to improve the homogeneity of the system and reduce local aggregation.

[0048] 4. The ion gel mixture obtained in step 3 is introduced into the microstructure region of the sapphire template, so that the solution covers the template surface and fills the gaps between the template arrays. The template uses a commercially available 2-inch patterned sapphire substrate wafer, i.e., a PSS wafer. PSS stands for Patterned Sapphire Substrate. The PSS wafer is a single-crystal α-Al2O3 sapphire hard substrate, and its patterned surface has an inverse pit structure corresponding to the nano-crown structure. In use, the 2-inch PSS wafer can be used as a whole as a template, or it can be cut into smaller template pieces according to the sensor size requirements. Since the PSS template is a hard sapphire substrate, it can be demolded by edge peeling after the ion gel has solidified. The template itself does not need to be removed by acid or alkali corrosion. After cleaning and drying, it can be reused for subsequent replication and molding of ion gel nano-crown structures.

[0049] 5: Place the sapphire template carrying the ionogel mixture in an oven and cure it at 80 °C for more than 4 hours to allow the solvent to evaporate and form a stable ionogel layer.

[0050] 6. After curing, remove the template and allow it to cool. Gently peel the ionogel layer from the edge with tweezers to demold, obtaining an ionogel layer with a nano-crown structure on the surface. Its SEM morphology can be found in [reference needed]. Figure 3 .

[0051] In a preferred embodiment, the nanocranial structure has a top platform region, sloping sidewalls, and a bottom transition region, exhibiting a polygonal outline in top view, preferably a hexagonal outline; its height is 200–260 nm, its lateral equivalent radius is 150–350 nm, and the center-to-center distance between adjacent nanocranial structures is 0.8–1.2 μm; the microstructure's equivalent radius is within the nanoscale range. This nanocranial structure can trigger more significant interfacial contact area modulation under relatively low pressure, thereby enhancing the double-layer capacitance change signal.

[0052] 7. To improve the fidelity and consistency of structural replication during multiple replication processes, the sapphire template can be cleaned and reused after the first curing and demolding. The cleaning and reuse process may include, but is not limited to, the following steps: Step 7-1: Solvent cleaning of the template surface to remove any residual ionomer gel or organic components. The solvent may be one or more of DMF, ethanol, isopropanol, or combinations thereof; Step 7-2: Ultrasonic cleaning of the template to further remove residues in the microstructure gaps; Step 7-3: Drying of the cleaned template, which may include nitrogen blowing, natural drying, or low-temperature drying; Step 7-4: Using the cleaned and dried template in the next round of ionomer gel mixing solution introduction and curing steps, thereby achieving template reuse. Through the above optional cleaning and reuse process, the impact of template surface residues on subsequent molding can be reduced, which is beneficial for maintaining the consistency and stability of microstructure replication. Simultaneously, the template can be reused multiple times, which helps reduce the dependence on expensive custom processing and disposable templates for nanostructure replication molding, thereby improving the engineering feasibility and promotional value of the present invention.

[0053] 8: Cut the ion gel layer to the predetermined size; the upper and lower electrodes are made of conductive copper tape electrodes, and the electrode surfaces are planar structures.

[0054] 9. Before bonding, the bonding surfaces of the ionogel layer and / or the electrode bonding surfaces are subjected to plasma treatment, preferably argon plasma treatment for 120 s, to improve the bonding stability of the interface and reduce the interface voids.

[0055] 10: The upper and lower electrodes are respectively bonded to the ion gel layer to form a sandwich structure, thus obtaining a sensor semi-finished product.

[0056] 11: The semi-finished product is fully encapsulated and sealed using a PI encapsulation layer, preferably with a thickness of about 0.1 mm, to obtain the finished product of the ionized flexible pressure sensor.

[0057] The ionogel of this invention has nano-crown protrusions on its surface, and the electrodes are planar (copper tape). This structure allows for: Under zero pressure: Only the top platform of the crown forms effective EDL contact with the electrode (extremely small area); Under slight pressure: the sidewalls of the crown platform are gradually "pressed" and unfolded → the effective contact area increases non-linearly; During the pressurization process, the crown platform undergoes a three-level geometric transition from the top surface to the slope to the root. Compared to existing technologies such as the pure side surface of the cylinder in CN109781312A and the smooth curved surface of the dome in CN120467418A, this invention makes the unfolding process of the crown platform more controllable during the pressurization process and realizes the progressive surface contact EDL modulation of the nano-crown platform array by the planar electrode, which is not disclosed in the prior art.

[0058] From a process perspective, this invention innovatively uses commercially available LED substrate PSS, leveraging the mature patterned substrate product line in the optoelectronic industry, and cross-borderly uses it as a demolding mold for ion gel nanoforming. This avoids the potential damage and complex steps to the ion gel caused by strong acid and strong alkali corrosion of the template in existing technologies such as CN109781312A, and achieves pure mechanical peeling and template reuse.

[0059] Example 2 This embodiment further introduces a PDMS frame-shaped intermediate layer based on embodiment 1, as shown in the schematic diagram below. Figure 5 As shown, the PDMS frame-shaped intermediate layer is disposed between the ionogel layer and the lower electrode to define the effective sensing area and reduce the initial capacitance, thereby improving assembly consistency and output signal readability. Except for the differences described below, the remaining steps are the same as or equivalent to those in Example 1.

[0060] Step 12: Mix the PDMS base agent and curing agent at a ratio of 10:1 and stir for 3–5 minutes until homogeneous.

[0061] Step 13: Place the PDMS mixture in a vacuum drying oven and evacuate for about 30 minutes to remove air bubbles.

[0062] Step 14: Pour the degassed PDMS solution into a pre-prepared PMMA plate mold. The PMMA plate is laser-processed to form a frame-shaped cavity. The outer edge of the frame-shaped cavity is 1.2 cm and the inner edge is 1.0 cm. The cavity height is preferably about 150 μm (or can be selected in the range of 100–300 μm).

[0063] Step 15: Place the PMMA board in an 80 ℃ drying oven to cure for about 2 hours. After curing, use tweezers to demold and remove the PDMS frame gasket.

[0064] Step 16: During assembly, place the PDMS frame-shaped pad between the ionogel layer and the lower electrode, so that the frame-shaped opening area corresponds to the effective sensing area; the overall size of the ionogel layer is preferably similar to the outer ring size (e.g., about 1.2 cm × 1.2 cm), so that the effective area defined by the frame-shaped opening is about 1.0 cm × 1.0 cm.

[0065] Step 17: Complete the bonding of the lower electrode, ion gel, and upper electrode within the frame-shaped opening area to form an effective EDL interface; then complete the device fabrication according to the plasma processing and encapsulation steps in Example 1.

[0066] The product involved in this invention belongs to the category of sensors, which require calibration before use. In order to prevent repeated calibration, the consistency requirements between different batches of products are high. The surface microstructure prepared by this invention is obtained by demolding. Therefore, the reusable PSS template and PDMS frame shape jointly promote the improvement of product consistency.

[0067] Sensor pressure response test.

[0068] The sensor's capacitance was measured using an LCR meter at a frequency of 1 kHz and an excitation voltage of 500 mV. The output signal can be expressed as either the capacitance change ΔC or the normalized capacitance change ΔC / C0; ΔC / C0 is preferred for sensitivity analysis and comparison, where C0 is the initial capacitance.

[0069] Pressure loading is achieved using a displacement loading mechanism driven by a stepper motor, which applies repeatable compression loading to the sensor by controlling the displacement.

[0070] To map the displacement load to the actual pressure value, the sensor was placed on a commercial foil pressure gauge for pressure calibration. The pressure was then read using the foil pressure gauge, and a pressure-capacitance (or ΔC / C0) response curve was established.

[0071] Cyclic loading tests can be performed to evaluate repeatability and stability, such as performing continuous cyclic loading at a set pressure amplitude and recording the capacitance response curve over time.

[0072] The PDMS frame-shaped interlayer has three functions: improving the sensing area, reducing initial capacitance, and suppressing edge squeezing, which can solve the problem of poor assembly consistency of ion-electric devices.

[0073] This invention solves the long-standing technical contradiction in the prior art of achieving a balance between "high sensitivity, wide measurement range, and low-cost preparation".

[0074] This invention creatively applies commercially available PSS sapphire substrates (originally used in the LED industry) to the micro / nano molding of ion gels. The single-crystal sapphire material of the PSS template possesses extremely high hardness, heat resistance, and chemical inertness. This characteristic creates a crucial synergy with the curing process of the ion gel precursor solution (80°C heating, DMF solvent environment): On the one hand, the rigid template ensures that during solvent evaporation and shrinkage, the ion gel can accurately replicate the unique crown morphology with a "top platform - sloping sidewalls - rounded bottom corners," avoiding the swelling and deformation that may occur with soft templates (such as PDMS) under high-temperature solvents; on the other hand, the chemical inertness of sapphire means that the template does not need to undergo strong acid and alkali corrosion as in existing technologies (CN109781312A) after demolding, requiring only simple cleaning for reuse. This combination of "rigid non-sacrificial template + specific polymer matrix (PVDF-HFP)" not only reduces costs but also ensures a high degree of consistency in the nano-crown structure of each batch, which is impossible to achieve with soft template transfer or sacrificial template methods.

[0075] The nano-crown structure and planar electrode configuration of this invention generate a unique "progressive surface contact" EDL modulation mechanism. Unlike existing micron-level dome interlocking structures or nanowire point contact structures, the crown structure of this invention features a flat top platform and a large slope angle. In the low-pressure stage, only the top platform forms an electric double layer, resulting in extremely low initial capacitance. As pressure increases, the inclined sidewalls gradually undergo elastic deformation and form surface contact with the planar electrodes. This "point (platform) line (edge) surface (sidewall)" contact evolution process causes the effective contact area to increase non-linearly with pressure. This interface physical evolution (progressive contact) guided by a specific geometry (crown structure) greatly optimizes the sensitivity and linearity of the ionization sensor, a technical effect that cannot be achieved simply by reducing the size of the micron structure.

[0076] The PDMS frame-shaped interlayer introduced in this invention is not simply a physical isolation layer, but rather forms a precise mechanical and electrical match with the nano-crown structure. The PDMS frame defines the effective sensing area, preventing ineffective compression of the ionogel layer in non-sensing areas and ensuring that pressure loads are accurately applied to the nano-crown array. Simultaneously, the frame thickness (100-300 μm) design allows the sensor to maintain a small pre-gap when not under pressure, further reducing the initial capacitance (C0). This combination of "nanoscale sensing unit (crown) + millimeter-scale confinement structure (PDMS frame)" effectively suppresses edge effects and assembly errors, significantly improving the signal consistency and repeatability of the device during mass production, and solving the engineering pain point of ionoelectric devices being difficult to implement due to large initial state fluctuations.

[0077] Comparison Example 1: Ionized Flexible Pressure Sensor without Microstructured Ion Gel Layer This comparative example is used to verify the contribution of the nanostructure array to the enhanced pressure response. The preparation steps are basically the same as in Example 1, except that instead of using a sapphire template to replicate the microstructure, an ionogel solution is cured on a flat substrate to obtain a smooth ionogel layer; subsequently, it is attached to the upper and lower electrodes and encapsulated in the same manner to obtain the control sensor.

[0078] The nanostructured ionogel sensor prepared in Example 1 and the unstructured ionogel sensor prepared in Control Example 1 were subjected to pressure-capacitance response tests under the same electrode materials, ionogel composition, device area, test frequency, and loading conditions. The test results are as follows: Figure 4 As shown, compared to ionogel layers without microstructure, ionogel layers with PSS template-replicated nanocluster structures exhibit more significant capacitance changes under pressure. This indicates that the nanocluster structure can enhance the effective contact area modulation of the electrode-ionogel interface during pressure application, thereby improving the pressure response capability of ionized pressure sensors.

[0079] In summary, this invention constructs a nano-crown structure by replicating and molding using a PSS template, enhancing the effective contact area modulation of the double electric layer while maintaining a simple and feasible process, thereby achieving ionized flexible pressure sensing. The PDMS frame-shaped interlayer further optimizes the initial capacitance and effective area, and combined with plasma treatment and packaging structure, improves the device assembly stability and application reliability.

Claims

1. An ionized flexible pressure sensor with a nano-crown structure, characterized in that, include: An upper electrode, a lower electrode, and an ion gel layer sandwiched between the upper electrode and the lower electrode; The ionogel layer is formed by combining a polymer matrix and an ionic liquid to form an ionogel material, and at least one side surface of the ionogel layer has an array of nano-crown protrusions. The nano-crown protrusion array is obtained by directly pouring ion gel precursor liquid into the surface pit structure of a patterned sapphire substrate PSS hard template and curing it, and then replicating it by a non-sacrificial peeling demolding method. The PSS hard template is a single crystal sapphire substrate with a periodically arranged inverted pit structure pre-formed on its surface. The PSS hard template retains structural integrity after demolding and can be reused for the next replication after cleaning. When external pressure is applied to the sensor, the effective contact area of ​​the double layer between the electrode surfaces of the upper and / or lower electrodes and the nano-crown protrusion array on the surface of the ion gel layer changes with the pressure, causing a change in the interfacial double layer capacitance, thereby achieving pressure detection.

2. The ionized flexible pressure sensor according to claim 1, characterized in that: The polymer matrix is ​​polyvinylidene fluoride-hexafluoropropylene copolymer PVDF-HFP, and the ionic liquid is selected from imidazole bis(trifluoromethanesulfonyl)imide salts; In the ionogel layer, the mass ratio of polymer matrix to ionic liquid enables the ionogel to form a flexible cross-linked network with peelable self-supporting properties, and the thickness of the ionogel layer is 0.3–0.8 mm.

3. The ionized flexible pressure sensor according to claim 1, characterized in that: Each crown protrusion in the nano-crown protrusion array has a top platform region, inclined sidewalls, and a bottom transition rounded corner region, and has a polygonal outline in the top-view projection direction; the height of the crown is 200–260 nm, the lateral equivalent radius of the crown structure is 150–350 nm, and the center-to-center distance between adjacent crowns is 0.8–1.2 μm.

4. The ionized flexible pressure sensor according to claim 1, characterized in that: The upper and lower electrodes are planar structure electrodes. The upper electrode and the ion gel layer, and the lower electrode and the ion gel layer, form an electrode-ion gel interface by direct attachment. The nano-crown protrusion array is arranged towards the planar structure electrode, so that the effective double-layer contact under low pressure mainly occurs in the top platform area of ​​the crown, and gradually expands to the inclined sidewall area as the pressure increases.

5. The ionized flexible pressure sensor according to claim 1, characterized in that, Also includes: A frame-shaped intermediate layer is disposed between the ionogel layer and the lower electrode or between the upper electrode and the ionogel layer; The frame-shaped interlayer is a hollow frame structure, with an effective sensing window area defined inside the frame. The thickness of the frame itself is in the range of 100–300 μm, and the frame-shaped interlayer is made of PDMS material. The frame-shaped intermediate interlayer constrains the effective double-layer contact between the ion gel layer and the electrode within the windowed area, thereby reducing the initial capacitance under no-pressure conditions and improving the assembly consistency between devices.

6. The ionized flexible pressure sensor according to claim 1, characterized in that: The interface between the ion gel layer and the electrode is subjected to plasma treatment before assembly to increase the surface energy; the sensor also includes a flexible encapsulation layer covering the outer surface of the layered structure composed of the upper electrode, the lower electrode, and the ion gel layer, the encapsulation layer being made of PI and having a thickness in the range of 0.05–0.15 mm.

7. The ionized flexible pressure sensor according to claim 1, characterized in that: The PSS rigid template is a commercially available patterned sapphire substrate wafer, whose surface inverted pit structure was originally used as a patterned substrate for LED epitaxial growth. The pits have an aperture of 300–700 nm, a depth of 200–260 nm, and a center-to-center spacing of 0.8–1.2 μm. The ion gel precursor liquid is filled into the pits and cured at 80–120 °C. The gel is then demolded from the PSS rigid template surface by mechanical peeling. After demolding, the surface of the ion gel is left with an array of nano-crown protrusions that are complementary to the pits.

8. The method for fabricating the ionized flexible pressure sensor according to any one of claims 1-7, characterized in that, Includes the following steps: S1. Preparation of ionogel precursor solution: Dissolve PVDF-HFP in DMF solvent, heat and stir until completely dissolved, add ionic liquid and continue stirring, then sonicate to obtain homogeneous ionogel precursor solution; S2. Take a commercially available PSS rigid template, clean and dry its surface, add the ion gel precursor liquid to the template surface and fill the reverse pit array on the template surface with the precursor liquid, and cure it at 75–120℃ for 2–6 h to allow the solvent to evaporate and the ion gel network to form. S3. Mechanically peel off the solidified ionogel layer from the edge of the PSS template to obtain a flexible ionogel layer with a nano-crown protrusion array on the surface. S4. The upper electrode and the lower electrode are respectively attached to the upper and lower sides of the ion gel layer to form a layered sandwich sensing structure. Plasma treatment is performed to improve the interface adhesion, and then flexible encapsulation is performed to obtain the ionized flexible pressure sensor. S5. After the PSS rigid template is demolded, it is solvent cleaned and / or ultrasonically cleaned, dried, and then returned to step S2 for reuse.

9. The preparation method according to claim 8, characterized in that: In step S1, the mass ratio of PVDF-HFP:DMF solvent:ionic liquid is 1:(4–7):(2–4); In step S2, the curing temperature is 80±5℃ and the curing time is ≥4 h; In step S3, the demolding method is purely mechanical peeling along the edge of the template, without involving acid or alkali corrosion to remove the template; In step S4, the bonding surface of the ionogel layer and / or the electrode surface are subjected to argon or oxygen plasma treatment for 60–180 s before bonding.

10. The preparation method according to claim 8, characterized in that, Also includes: Preparation of PDMS frame-shaped gaskets; A PDMS frame-shaped pad is placed between the ionogel layer and the lower electrode, so that the opening area of ​​the frame-shaped pad corresponds to the effective sensing area. The lower electrode, ion gel, and upper electrode are bonded together within the opening area of ​​the frame-shaped gasket.

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