Capacitive flexible pressure sensor based on double-sided hierarchical microstructure and preparation method thereof

Abstract

The invention relates to a capacitive flexible pressure sensor based on a double-sided hierarchical microstructure and a preparation method of the capacitive flexible pressure sensor, and belongs to the technical field of sensors. An upper flexible electrode layer; an ion sensitive layer; an isolation layer; an ionic gel layer; an intermediate support layer; a lower flexible electrode layer; and a lower encapsulation layer. According to the invention, by designing the double-sided graded microstructure, the ion sensitive layer and the ion gel layer can respond step by step under different pressures, so that the top of the microstructure is contacted at first under low pressure, and high sensitivity is provided; as the pressure is increased, the microstructure gradually topples over, and the contact area is increased, so that linear response is kept in a wide pressure range, and the problems that the sensitivity and the measuring range cannot be obtained at the same time, the response / recovery speed is low, the structure collapses and lags, and the EDL area utilization rate is low are solved.

Description

Technical Field

[0001] This invention relates to the field of transistor manufacturing technology, and in particular to a capacitive flexible pressure sensor based on a bifacial hierarchical microstructure and its fabrication method. Background Technology

[0002] Capacitive structures have become one of the mainstream implementation methods for flexible pressure sensors due to their simple structure, low power consumption, small temperature drift, and good compatibility with standard readout circuits. The basic mechanism is as follows: when external pressure reduces the dielectric layer thickness d or increases the equivalent dielectric constant ε, the parallel plate capacitance C = εA / d increases accordingly. To improve the sensitivity ΔC / ΔP, current research mainly follows the following three technical routes: (1) Reduce the effective Young's modulus of the dielectric layer - introduce microstructures such as micropores, pyramids, hemispheres, and cylinders inside / on the surface of the elastomer so that the device can produce large deformation under small pressure; (2) Increase the amplitude of dielectric constant change - use ion gel, ion liquid-polymer composite, high κ ceramic-elastomer composite, etc. as dielectric layer, and utilize pressure-induced percolation or nonlinear dielectric constant enhancement effect; (3) Increasing the effective area or introducing electric double layer (EDL) capacitance—When the ion gel comes into contact with the conductive electrode, a nanoscale EDL is formed at the solid-liquid interface, and its capacitance per unit area can reach tens of μF cm⁻¹. -2 It is 3-4 orders of magnitude higher than that of traditional parallel plate capacitors, thus significantly amplifying ΔC.

[0003] Existing technologies still have the following common problems: (1) Natural templates have strong randomness and poor batch consistency, which cannot meet the requirements of controllable manufacturing; (2) 3D printing or laser processing is inefficient and expensive, which is not conducive to large-scale production; (3) Under high pressure, single-sided multi-level structures are prone to "tilting-stacking" of adjacent microstructures, resulting in plastic deformation, signal drift and hysteresis; (4) EDL is only formed at the interface between planar electrode and ion gel, and the usable area is limited by two-dimensional geometry, so the capacitance change cannot be further amplified; (5) Thick dielectric layers or high-viscosity ion gels result in long ion migration times and response / recovery speeds typically in the order of hundreds of milliseconds, making it difficult to detect high-frequency vibrations (>50 Hz). Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide a capacitive flexible pressure sensor based on a double-sided hierarchical microstructure and its fabrication method, in order to solve one of the problems of incompatibility between sensitivity and range, slow response and recovery speed, structural collapse and hysteresis, and low EDL area utilization.

[0005] This invention discloses a capacitive flexible pressure sensor based on a double-sided hierarchical microstructure, which, from top to bottom along the thickness direction, consists of: an upper encapsulation layer; an upper flexible electrode layer; and an ion-sensitive layer. Isolation layer; Ion gel layer; Intermediate support layer; Lower flexible electrode layer; Lower encapsulation layer; The lower surface of the upper flexible electrode layer is bonded to the upper surface of the ion-sensitive layer to form a first interface; The lower surface of the ion-sensitive layer is provided with a first microstructure, and the upper surface of the ion gel layer is provided with a second microstructure. The first microstructure and the second microstructure are arranged facing each other and staggered along the in-plane direction. The isolation layer is a continuous closed frame. The upper surface of the isolation layer is in contact with the periphery of the lower surface of the ion-sensitive layer, and the lower surface of the isolation layer is bonded to the periphery of the upper surface of the ion gel layer, so that the first microstructure and the second microstructure maintain a non-contact air gap under zero pressure. The lower surface of the ion gel layer is bonded to the upper surface of the lower flexible electrode layer through an intermediate support layer to form a second interface; The upper encapsulation layer completely covers the upper surface of the upper flexible electrode layer, and the lower encapsulation layer completely covers the lower surface of the lower flexible electrode layer; the outer edges of the upper and lower encapsulation layers are bonded to each other, and the ion-sensitive layer, the isolation layer, the ion gel layer, the intermediate support layer, and the sidewalls of the lower flexible electrode layer are completely sealed to form a fully sealed structure.

[0006] Preferably, the depth of the first microstructure in the ion-sensitive layer is 30 μm to 40 μm; and the depth of the second microstructure in the ion gel layer is 80 μm to 120 μm.

[0007] Preferably, the angle between the first microstructure in the ion-sensitive layer and the plane of the ion-sensitive layer is 60°~70°; the angle between the second microstructure in the ion gel layer and the plane of the ion gel layer is 60°~70°.

[0008] Preferably, the ion-sensitive layer is based on a microstructured elastomer with a two-dimensional material coated on its surface.

[0009] Preferably, the two-dimensional material is one or more of two-dimensional transition metal carbides / nitrides, graphene and its derivatives, two-dimensional transition metal sulfides, two-dimensional metal oxides, or carbon nanotube films. This invention also discloses a method for fabricating a capacitive flexible pressure sensor based on a bifacial hierarchical microstructure, which includes the following steps: S1: Two sets of microstructure molds with different depths and a certain tilt angle are obtained by two tilting photolithography. One set of microstructure molds is used to prepare an ion-sensitive layer with a first microstructure on one side of the surface. The other set of microstructure molds is used to prepare an ion gel layer with a second microstructure on one side of the surface. The tilt angles of the two sets of microstructure molds are matched so that the first microstructure and the second microstructure are set facing each other and staggered along the in-plane direction. S2: Print an isolation layer on the side of the ionogel layer that has the second microstructure; S3: The side of the ion-sensitive layer with the first microstructure is stacked with the side of the ion gel layer with the second microstructure facing each other, so that the first microstructure and the second microstructure are misaligned and the isolation layer is located between the ion-sensitive layer and the ion gel layer to obtain a pressure sensor preform. S4: The upper flexible electrode layer, the pressure sensor preform, the middle support layer, and the lower flexible electrode layer are stacked in sequence and then packaged to obtain the finished flexible pressure sensor.

[0010] Preferably, step S1 includes: S101: A microstructure mold consisting of a silicon wafer and microstructures at a certain tilt angle to the silicon wafer is fabricated using photolithography. During the exposure process, a certain angle must be maintained between the silicon wafer and the incident light so that the microstructures in the microstructure mold have a tilt angle. S102: A microstructured elastomer is prepared using a pre-made microstructured mold, cured by heating, and then peeled off to complete the preparation of the ion-sensitive layer; S103: Prepare an ion gel solution by pouring the ion gel solution into a microstructure mold and allowing it to solidify before peeling it off from the mold to complete the preparation of the ion gel layer.

[0011] Preferably, step S101 includes: adjusting the microstructure depth in the microstructure mold by adjusting the rotation speed and time of the spin coater.

[0012] Preferably, in step S101, the angle between the silicon wafer and the incident light is 20°~30°.

[0013] Preferably, step S102 further includes: coating a two-dimensional material on the surface of the ion-sensitive layer.

[0014] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: (1) This invention designs a double-sided hierarchical microstructure, which enables the ion-sensitive layer and the ion gel layer to respond stepwise under different pressures. At low pressure, the top of the microstructure contacts first, providing high sensitivity. As the pressure increases, the microstructure gradually tilts, increasing the contact area, thereby maintaining a linear response over a wide pressure range, solving the problem of the incompatibility between sensitivity and range. The sensitivity is 27 kPa⁻¹~36 kPa⁻¹, the range is 0~250 kPa, the response time is 15~35 ms, the recovery time is ≤25 ms, and the minimum detection is 0.8 Pa.

[0015] (2) The design of the isolation layer in this invention ensures that there is sufficient gap between the ion-sensitive layer and the ion gel layer under no pressure, avoiding unnecessary capacitance changes. When subjected to pressure, the rapid contact of the microstructure and the rapid recovery after pressure release enable the sensor to have a rapid response (≤15ms) and a recovery time (≤25ms), thereby solving the problem of slow response / recovery speed.

[0016] (3) The design of the double-sided hierarchical microstructure in this invention enables the microstructure to tilt in an directional manner under high pressure, avoiding the stacking and collapse between adjacent microstructures; the use of the isolation layer further ensures that the microstructure can quickly return to the initial state after the pressure is released, reducing structural collapse and hysteresis, improving the stability and repeatability of the sensor, thereby ensuring that the capacitance drift is <5% after 5000 cycles.

[0017] (4) The present invention forms a two-stage ladder with a height difference Δh≈50μm~80μm by the first microstructure in the ion-sensitive layer and the second microstructure in the ion gel layer. The two-stage depth difference forms a step-by-step contact sequence, taking into account both low pressure and high sensitivity and high pressure and long stroke. The same set of sensors can achieve continuous coverage of "low pressure and high sensitivity - high pressure and wide range" and realize linear output of the full range of 0~250kPa.

[0018] (5) The present invention obtains a double-sided graded mold by performing only two photolithography-molding processes, and completes the preparation of electrodes and isolation layers with flexible electronic printing. It eliminates the need for 3D printing or multiple alignments, reduces process complexity by more than 50%, and achieves low-cost mass production compatible with roll-to-roll.

[0019] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0020] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. Figure 1 This is a layered explosion diagram of a double-sided hierarchical microstructure capacitive flexible pressure sensor according to one embodiment of the present invention. Figure 2a for Figure 1 A three-dimensional simulation model of the double-sided hierarchical microstructure in the implementation method; Figure 2b for Figure 2a Enlarged view of a specific area; Figure 3 Figure 2 shows the simulation results of the contact area change of the microstructure under progressive pressure. Figure 4 For preparation Figure 1 A schematic diagram of the photolithography exposure angle used when creating tilted microstructures; Figure 5 for Figure 1 Scanning electron microscope image of the double-sided hierarchical microstructure mold in the embodiment; Figure 6 for Figure 1 Photographs of the actual surface morphology of the ion-sensitive layer in the implementation method; Figure 7 for Figure 1 Photographs of the actual surface morphology of the ionogel layer in the implementation method; Figure 8a for Figure 1 The implementation method includes a schematic diagram of the isolation layer printing process and a top view of the finished product; Figure 8b for Figure 8a Enlarged view of a specific area; Figure 9 For testing Figure 1 Images of a pressure-capacitive data acquisition platform for sensor performance; Figure 10 for Figure 1 Response / recovery time curves of the sensor under step pressure; Figure 11 for Figure 1 Sensor capacitance-pressure calibration curve; Figure 12 for Figure 1 A pulse waveform captured when the sensor is attached to the wrist; Figure 13 for Figure 1 A graph of bending-capacitance signals collected when the sensor is attached to a finger joint; Figure 14 for Figure 1Capacitive response diagram of vocal cord vibration (producing "a / b / c") when the sensor is attached to the neck.

[0021] Figure label: 5a - Upper encapsulation layer; 1a - Upper flexible electrode layer; 2-Ion-sensitive layer; 21-First microstructure; 3-Isolation layer; 4-Ion gel layer; 41-Second microstructure; 6-Intermediate support layer; 1b - Lower flexible electrode layer; 5b - Lower encapsulation layer. Detailed Implementation

[0022] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0023] On one hand, this invention discloses a capacitive flexible pressure sensor based on a double-sided hierarchical microstructure, such as... Figure 1-14 As shown, the pressure sensors are arranged from top to bottom along the thickness direction as follows: Upper encapsulation layer 5a; Upper flexible electrode layer 1a; Ion-sensitive layer 2; Isolation layer 3; Ion gel layer 4; Intermediate support layer 6; Lower flexible electrode layer 1b; Lower encapsulation layer 5b; The lower surface of the upper flexible electrode layer 1a is bonded to the upper surface of the ion-sensitive layer 2 to form a first interface. The lower surface of the ion-sensitive layer 2 is provided with a first microstructure 21, and the upper surface of the ion gel layer 4 is provided with a second microstructure 41. The first microstructure 21 and the second microstructure 41 are arranged facing each other and staggered along the in-plane direction. The isolation layer 3 is a continuous closed frame. The upper surface of the isolation layer 3 is in contact with the periphery of the lower surface of the ion-sensitive layer 2, and the lower surface of the isolation layer 3 is bonded to the periphery of the upper surface of the ion gel layer 4, so that the first microstructure 21 and the second microstructure 41 maintain a non-contact air gap when there is zero pressure. The lower surface of the ion gel layer 4 is bonded to the upper surface of the lower flexible electrode layer 1b through the intermediate support layer 6, forming a second interface; The upper encapsulation layer 5a completely covers the upper surface of the upper flexible electrode layer 1a, and the lower encapsulation layer 5b completely covers the lower surface of the lower flexible electrode layer 1b; the outer edges of the upper encapsulation layer 5a and the lower encapsulation layer 5b are bonded to each other, and the ion-sensitive layer 2, the isolation layer 3, the ion gel layer 4, the intermediate support layer 6, and the sidewall of the lower flexible electrode layer 1b are completely sealed to form a fully sealed structure.

[0024] During implementation, the first microstructure on the lower surface of the ion-sensitive layer 2 interacts with the second microstructure 41 on the upper surface of the ion gel layer 4, which helps to increase the contact area between them under pressure, thereby increasing the capacitance change of the pressure sensor, amplifying the double layer effect, and thus improving the sensitivity of the pressure sensor to pressure. The isolation layer 3 is placed between the ion-sensitive layer 2 and the ion gel layer 4 to ensure that the two do not come into contact with each other when there is no pressure, and at the same time, it allows the pressure sensor to quickly return to its initial state when the pressure is removed. The upper encapsulation layer 5a and the lower encapsulation layer 5b can provide protection for the overall structure of the pressure sensor, preventing environmental factors such as humidity and dust from damaging the internal structure of the sensor, while enhancing mechanical stability and durability. The upper flexible electrode layer 1a and the lower flexible electrode layer 1b serve as two electrodes of the pressure sensor, capable of outputting the pressure signal generated by the pressure sensor. The above arrangement and setup, through the design of a double-sided hierarchical microstructure, can achieve linear response and rapid response and recovery within different pressure ranges. The isolation layer can prevent false triggering under no-pressure conditions, improve the stability of the sensor, and thus achieve high-sensitivity pressure detection while improving the sensor's sensitivity, response speed, and stability. It also provides a large bandwidth and operating range for pressure detection to meet the needs of various application scenarios.

[0025] Compared with existing technologies, this invention designs a double-sided hierarchical microstructure, which enables the ion-sensitive layer and the ion gel layer to respond stepwise under different pressures. At low pressure, the top of the microstructure contacts first, providing high sensitivity. As the pressure increases, the microstructure gradually tilts, increasing the contact area, thereby maintaining a linear response over a wide pressure range, solving the problem of the trade-off between sensitivity and range.

[0026] Compared with existing technologies, the isolation layer design in this invention ensures sufficient gap between the ion-sensitive layer and the ion gel layer under no pressure, avoiding unnecessary capacitance changes. When subjected to pressure, the rapid contact of the microstructure and the rapid recovery after pressure release enable the sensor to achieve a fast response (≤15ms) and recovery time (≤25ms), thereby solving the problem of slow response / recovery speed.

[0027] Compared with the prior art, the design of the double-sided hierarchical microstructure in this invention enables the microstructure to tilt in an directional manner under high pressure, avoiding the stacking and collapse between adjacent microstructures; the use of the isolation layer further ensures that the microstructure can quickly return to its initial state after the pressure is released, reducing structural collapse and hysteresis, improving the stability and repeatability of the sensor, and ensuring that the capacitance drift is <5% after 5000 cycles.

[0028] Compared with the prior art, the technical effects achieved by the present invention include: High-sensitivity detection: By setting bifacial hierarchical microstructures of different heights on the surfaces of the ion-sensitive layer 2 and the ion gel layer 4, high-sensitivity detection under minute pressures (0-0.25 kPa) was achieved, with a sensitivity ≥36.46 kPa. -1 .

[0029] Wide detection range: The hierarchical design of the microstructure enables the sensor to maintain a linear response over a wide pressure range of 0.25 kPa to 250 kPa, making it suitable for a variety of applications.

[0030] Rapid response and recovery: The design of the isolation layer ensures that the sensor responds quickly (15ms) when stimulated by pressure and recovers quickly (25ms) after the pressure is released, making it suitable for dynamic pressure monitoring.

[0031] Low detection limit: The sensor can detect very small pressure changes, such as vocal tract vibrations, with a minimum detection limit of ≤0.8 Pa.

[0032] Good stability and repeatability: After 5000 cycles of loading, the capacitance drift is less than 5%, demonstrating good long-term stability and repeatability.

[0033] Easy to prepare and cost-effective: Using conventional photolithography processes and materials, without the need for high-precision 3D printing technology, the preparation complexity and cost are reduced, which is conducive to mass production.

[0034] Preferably, the depth of the first microstructure in the ion-sensitive layer is 30 μm to 40 μm; and the depth of the second microstructure in the ion gel layer is 80 μm to 120 μm.

[0035] It should be noted that the first microstructure in the ion-sensitive layer and the second microstructure in the ion gel layer form a two-stage ladder with a height difference Δh≈50μm~80μm, aiming to achieve continuous coverage of "low pressure high sensitivity - high pressure wide range" using the same sensor. Low-pressure zone (0–0.25 kPa): Only the shallow column at the top, 30–40 μm in diameter, contacts the opposite plane first. The actual contact area is small, so even a small pressure can produce a large area change rate ΔA / A, and the sensitivity is amplified to 36 kPa⁻¹.

[0036] Medium and high pressure range (0.25kPa–250kPa): After the shallow column is gradually poured to its limit, the 80–120 μm deep column begins to participate in the contact, and the effective area continues to expand linearly, avoiding "bottoming out" hardening. This allows the capacitance to continue to rise with pressure, and the range extends to 250 kPa while maintaining a correlation R²>0.99.

[0037] Anti-stacking and springback: The height difference ensures that the deep column is in standby mode under low pressure, preventing adjacent columns from tilting and interlocking at the same time; when the pressure is released, the shallow column recovers first, causing the deep column to spring back, reducing plastic deformation and hysteresis.

[0038] Process tolerance: Shallow structures of 30μm~40μm have low requirements for photoresist thickness uniformity and the highest yield; deep structures of 80μm~120μm are independently controlled through secondary photolithography, and depth errors can be compensated individually, resulting in better overall reproducibility.

[0039] Compared with the prior art, the present invention forms a two-stage ladder with a height difference Δh≈50μm~80μm by the first microstructure in the ion-sensitive layer and the second microstructure in the ion gel layer. The two-stage depth difference forms a step-by-step contact sequence, which takes into account both low pressure and high sensitivity and high pressure and long stroke. The same set of sensors can achieve continuous coverage of "low pressure and high sensitivity - high pressure and wide range" and realize linear output of the full range of 0~250kPa.

[0040] Compared with existing technologies, this invention obtains a double-sided graded mold by performing only two photolithography-molding processes, and completes the preparation of electrodes and isolation layers with flexible electronic printing. It eliminates the need for 3D printing or multiple alignments, reduces process complexity by more than 50%, and achieves low-cost mass production compatible with roll-to-roll.

[0041] Preferably, the angle between the first microstructure in the ion-sensitive layer and the plane of the ion-sensitive layer is 60°~70°; the angle between the second microstructure in the ion gel layer and the plane of the ion gel layer is 60°~70°.

[0042] It should be noted that the aforementioned angle setting ensures that the micro-columns bend only in the "downhill" direction when under pressure, and that adjacent columns are staggered due to the alternating tilt directions, thus preventing the "head-to-head" locking common in vertical columns. This maximizes the rebound torque coefficient of the microstructure, allowing it to fully reset within 25ms after unloading, further reducing hysteresis. At the same time, it reduces the initial contact area by approximately 35% compared to vertical columns, increasing ΔC / C0 by 1.4 times. Simultaneously, the root cross-sectional area increases by approximately 1 / sin65°, resulting in an increase in compressive strength rather than a decrease, balancing high signal strength and long lifespan.

[0043] Specifically, the upper flexible electrode layer 1a and the lower flexible electrode layer 1b can be made of silver nanowires, gold nanowires, graphene ink or carbon nanotube ink to ensure the continuity and conductivity of the electrodes when the sensor is bent or stretched, thereby maintaining the stability of the sensor performance.

[0044] Specifically, the thickness of the upper flexible electrode layer 1a and the lower flexible electrode layer 1b is 20μm~50μm, which can be 20μm, 25μm, 30μm, 35μm, 40μm, 45μm or 50μm.

[0045] It should be noted that the thickness of the upper flexible electrode layer 1a and the lower flexible electrode layer 1b is less than 20μm, and the sudden increase in surface resistance leads to signal attenuation; printing requires single-pass molding, resulting in large thickness errors and a decrease in yield; although bending is more flexible, the curing stress on the PI substrate is too low, which easily leads to "wrinkling" defects. The upper flexible electrode layer 1a and the lower flexible electrode layer 1b are larger than 50μm. The bending radius increases sharply, making it impossible to fit the skin / joint. At the same time, the ink consumption and cost increase linearly. This results in an error of >3μm after multiple printing passes. The microstructure is easily "crushed" by the hard electrodes, and the sensitivity decreases.

[0046] Specifically, the upper encapsulation layer 5a and the lower encapsulation layer 5b can be selected as polyimide (PI) films, and the thickness of the upper encapsulation layer 5a and the lower encapsulation layer 5b is 25μm~100μm, which can be 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 55μm, 60μm, 65μm, 70μm, 75μm, 80μm, 85μm, 90μm, 95μm or 100μm.

[0047] It should be noted that when the thickness of the upper encapsulation layer 5a and the lower encapsulation layer 5b is less than 25μm, the tensile strength of the PI film is <120MPa, and it is easy to tear after encapsulation; when the thickness of the upper encapsulation layer 5a and the lower encapsulation layer 5b is greater than 100μm, the bending stiffness is proportional to the cube of the thickness, and the bending radius is >10mm, which is greater than the curvature of the wrist / finger joint.

[0048] Preferably, the upper encapsulation layer 5a and the lower encapsulation layer 5b are made of polyimide (PI) film material. Polyimide (PI) film material has good heat resistance, chemical stability and mechanical strength. At the same time, the PI film has strong adhesion to the ion gel layer, which can prevent slippage and avoid the relative position displacement of the electrode layer and the ion gel layer. It also separates the electrode layer and the dielectric layer to prevent voltage breakdown and protect the electrode.

[0049] Specifically, the thickness of the intermediate support layer 6 is 40μm to 65μm, which can be 40μm, 45μm, 50μm, 55μm, 60μm or 65μm.

[0050] It should be noted that when the intermediate support layer 6 is a PI film, if the thickness is less than 40 μm, the pinhole density of the PI film increases sharply, and the breakdown field strength drops from 280 V / μm to below 180 V / μm, increasing the risk of breakdown at a 5V working voltage. At the same time, insufficient film thickness cannot fill the unevenness of the lower flexible electrode layer of 20 μm–50 μm, resulting in local stress concentration in the ion gel layer.

[0051] When the thickness of the intermediate support layer 6 exceeds 65μm, the bending stiffness is proportional to the cube of the thickness. The minimum bending radius of the overall sensor increases from 5mm to more than 10mm, which exceeds the curvature of the wrist / finger joint.

[0052] Specifically, the ion-sensitive layer 2 is based on a microstructured elastomer with a two-dimensional material coated on its surface.

[0053] Specifically, the two-dimensional material can be one or more of the following: two-dimensional transition metal carbon / nitrides, graphene and its derivatives, two-dimensional transition metal sulfides (e.g., molybdenum disulfide), two-dimensional metal oxides, or carbon nanotube films.

[0054] In implementation, the ion-sensitive layer 2 is coated with a two-dimensional material (such as MXene). The ion-sensitive layer uses a microstructured elastomer as its substrate; the microstructure helps increase the contact area with the ion gel layer under pressure, thereby increasing capacitance change, amplifying the electric double layer effect, and improving the sensor's sensitivity to pressure. By coating the ion-sensitive layer with the two-dimensional material MXene, the electric double layer effect is amplified, further improving the sensor's sensitivity.

[0055] Compared with existing technologies, this invention increases the contact area with the ion gel layer by coating the surface of the ion-sensitive layer with a two-dimensional material with a high specific surface area, such as MXene, thereby enhancing the electric double layer effect (EDL) and improving the capacitance. This design fully utilizes the high capacitance characteristics of EDL, further improving the sensor's sensitivity and solving the problem of low EDL area utilization.

[0056] Specifically, the thickness of the microstructured elastomer ranges from 500 μm to 2000 μm, and can be 500 μm, 550 μm, 600 μm, 650 μm, 700 μm, 750 μm, 800 μm, 850 μm, 900 μm, 950 μm, 1000 μm, 1050 μm, 1100 μm, 1150 μm, 1200 μm, 1250 μm, 1300 μm, 1350 μm, 1400 μm, 1450 μm, 1500 μm, 1550 μm, 1600 μm, 1650 μm, 1700 μm, 1750 μm, 1800 μm, 1850 μm, 1900 μm, 1950 μm, or 2000 μm.

[0057] It should be noted that when the thickness of the microstructured elastomer is less than 500 μm, the total height of the microstructure is only 35 μm-100 μm. After being compressed, the compressibility of the elastomer body is less than 10%, and it will "bottom out" and harden within a wide range of 0–250 kPa, resulting in a sharp drop in linearity. When the thickness of the microstructured elastomer is greater than 2000 μm, the thickness increases approximately linearly with the thermosetting time, and the compression set rate increases from 2% to 8%, leading to a decrease in stability.

[0058] Specifically, the material of the microstructured elastomer is one or a combination of PDMS, hydrogel, silicone, and TPU.

[0059] Specifically, the isolation layer 3 can be an insulating flexible material, such as silicone, with a thickness of 80μm to 120μm, which can be 80μm, 85μm, 90μm, 95μm, 100μm, 105μm, 110μm, 115μm or 120μm.

[0060] It should be noted that the thickness of the isolation layer 3 is 80μm~120μm, which can ensure a pressureless isolation gap of ≥10μm and a springback recovery force of 0.2–0.4Ncm⁻², while maintaining high sensitivity and single-print accuracy. It is the thinnest and safest thickness that balances performance and process.

[0061] Specifically, the thickness of the ionogel layer 4 ranges from 3000μm to 5000μm, and can be 3000μm, 3200μm, 3400μm, 3600μm, 3800μm, 4000μm, 4200μm, 4400μm, 4600μm, 4800μm or 5000μm.

[0062] It should be noted that the thickness of the ion gel layer 4 ranges from 3000μm to 5000μm, which ensures sufficient ion storage to maintain high EDL capacitance, while controlling the response / recovery time within 15ms / 25ms. It is also compatible with existing photolithography-molding processes and is the thinnest usable thickness that balances sensitivity, speed and mass production.

[0063] Specifically, the ionogel layer 4 is prepared from a gel component and an ion salt component, wherein the gel component is one or more of TPU, SEBS, POE, TPEE, PMMA, PBMA, polybutyl acrylate, PVDF-HFP, NBR and XSBR; and the ion salt component is one or more of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, N-butyl-N-methylpyrrolidine bisimide salt, triethylbutylammonium bisimide salt, LiTFSI and LiFSI.

[0064] On the other hand, this invention discloses a method for fabricating a capacitive flexible pressure sensor based on a bifacial hierarchical microstructure, comprising: S1: Two sets of microstructure molds with different depths and a certain tilt angle are obtained by two tilting photolithography. One set of microstructure molds is used to prepare an ion-sensitive layer with a first microstructure on one side of the surface. The other set of microstructure molds is used to prepare an ion gel layer with a second microstructure on one side of the surface. The tilt angles of the two sets of microstructure molds are matched so that the first microstructure and the second microstructure are set facing each other and staggered along the in-plane direction. S2: Print an isolation layer on the side of the ionogel layer that has the second microstructure; S3: The side of the ion-sensitive layer with the first microstructure is stacked with the side of the ion gel layer with the second microstructure facing each other, so that the first microstructure and the second microstructure are misaligned and the isolation layer is located between the ion-sensitive layer and the ion gel layer to obtain a pressure sensor preform. S4: The upper flexible electrode layer, the pressure sensor preform, the middle support layer, and the lower flexible electrode layer are stacked in sequence and then packaged to obtain the finished flexible pressure sensor.

[0065] In practice, the above-mentioned preparation method can achieve hierarchical processing of microstructures and can achieve high-precision control over the morphology of hierarchical microstructures. It avoids the randomness and high error of hierarchical microstructures made using natural templates such as sandpaper and leaves, and also avoids the problems of large material limitations and demanding equipment requirements caused by using high-precision 3D printing technology to make hierarchical microstructures.

[0066] Compared with existing technologies, this invention designs a double-sided hierarchical microstructure, which enables the ion-sensitive layer and the ion gel layer to respond stepwise under different pressures. At low pressure, the top of the microstructure contacts first, providing high sensitivity. As the pressure increases, the microstructure gradually tilts, increasing the contact area, thereby maintaining a linear response over a wide pressure range, solving the problem of the trade-off between sensitivity and range.

[0067] Specifically, step S1 includes: S101: A microstructure mold consisting of a silicon wafer and microstructures at a certain tilt angle to the silicon wafer is fabricated using photolithography. During the exposure process, a certain angle must be maintained between the silicon wafer and the incident light so that the microstructures in the microstructure mold have a tilt angle. S102: A microstructured elastomer is prepared using a pre-made microstructured mold, cured by heating, and then peeled off to complete the preparation of the ion-sensitive layer; S103: Prepare an ion gel solution. Pour the ion gel solution into a microstructure mold. After solidification, slowly peel it off from the mold to complete the preparation of the ion gel layer.

[0068] Specifically, step S101 includes: S1011: Take a single-sided polished silicon wafer and perform air blowing, baking and ion cleaning pretreatment; S1012: Photoresist is spin-coated onto the polished surface of a silicon wafer and then cured; S1013: After attaching the photoresist to the mask on the silicon wafer, the angle between the silicon wafer and the incident light is controlled for exposure; S1014: A silicon wafer with a microstructure on its surface is obtained after development.

[0069] Preferably, in step S1013, the angle between the silicon wafer and the incident light is between 20° and 30°, thereby preparing an ion gel layer and an ion-sensitive layer with a microstructure tilted at an angle of 60° to 70° to the ground.

[0070] Preferably, step S1012 is performed on a spin coater, and the depth of the microstructure in the microstructure mold is adjusted by adjusting the spin coater speed and time.

[0071] As an example, the process for fabricating the microstructure mold of the ion-sensitive layer meets the following requirements: By operating at 400 r / min to 600 r / min for 4 to 8 seconds, and then at 2000 r / min to 4000 r / min for 20 to 40 seconds, a microstructure mold with a depth of 30 μm to 40 μm can be obtained.

[0072] As an example, the process for fabricating the microstructure mold of the ionogel layer meets the following requirements: By operating at 80 r / min to 120 r / min for 4 to 8 seconds, and then at 1200 r / min to 1800 r / min for 20 to 40 seconds, microstructure molds with a depth of 80 μm to 120 μm can be obtained.

[0073] Preferably, the exposure time in step S1013 is 4s to 10s.

[0074] Specifically, step S102 includes: S1021: Fix the prepared silicon wafer with microstructure as a mold on the spin coater, pour the elastomer solution into the mold, set the speed and time of the spin coater, and perform spin coating. S1022: When less than 10 4 Degas for 10-30 minutes under vacuum. S1023: Dry at 60℃~70℃ for 1h~2h to complete the preparation of the ion-sensitive layer.

[0075] Specifically, in step S1021, the elastomer solution is a solution of one or more of PDMS, hydrogel, silicone, and TPU.

[0076] Specifically, the rotation speed and time of the spin coater in step S1021 are set as follows: 400r / min~600r / min for 4s~8s, then 2000r / min~4000r / min for 20s~40s.

[0077] It should be noted that a speed of 400r / min to 600r / min for 4s to 8s can quickly spread the photoresist (or elastomer solution) across the entire silicon wafer, eliminating pinholes and radial streaks, while preventing premature solvent evaporation that could lead to increased viscosity; the high-speed range of 2000–4000r / min for 20–40s can precisely thin the photoresist layer to the target thickness and homogenize it.

[0078] If only low speed is used: the adhesive layer is thick and has poor uniformity, which cannot meet the high aspect ratio requirements of microstructure molds; if only high speed is used: the adhesive is instantly thrown out of the edge, resulting in "central voids" or radial missing adhesive, and the mold is partially unfilled with adhesive, leading to the subsequent loss of microstructure.

[0079] Preferably, step S1024 is provided after step S1023: a two-dimensional material is coated on the surface of the ion-sensitive layer.

[0080] Pretreatment of the ion-sensitive layer by vacuum immersion in a bridging reagent solution for 18-26 hours can overcome the problem of low bonding strength between the two-dimensional material and the ion-sensitive layer, which makes it easy to fall off. After vacuum immersion pretreatment, the ion-sensitive layer was dried at 50℃~60℃ for 4h~6h, then immersed in a 1mg / mL~5mg / mL two-dimensional material dispersion, and dried at 50℃~60℃ to obtain an ion-sensitive layer with a two-dimensional material coating on its surface.

[0081] Specifically, the two-dimensional material can be one or more of the following: two-dimensional transition metal carbon / nitrides, graphene and its derivatives, two-dimensional transition metal sulfides (e.g., molybdenum disulfide), two-dimensional metal oxides, or carbon nanotube films.

[0082] Specifically, the bridging reagent solution can be a solution of one or more of chitosan and its derivatives, polyethyleneimine, polydiallyldimethylammonium chloride, or gelatin.

[0083] Specifically, the bridging reagent solution concentration is 0.1 mg / ml to 0.5 mg / ml. This concentration provides sufficient bridging efficiency and sufficient bridging effect within a limited time.

[0084] During implementation, bridging reagents and two-dimensional materials are used to achieve "molecular-level bridging + defect-free full coverage + high adhesion" on the surface of the ion-sensitive layer, ultimately increasing the specific capacitance of the double layer by 3-4 orders of magnitude while meeting long-term cycling stability requirements.

[0085] Specifically, step S103 includes: S1031: Place the prepared silicon wafer with microstructure as a mold on a horizontal platform, and slowly pour the prepared ion gel liquid onto the silicon wafer to completely cover the mold. S1032: Place in a fume hood at room temperature for 8-16 hours; S1033: Separate the cured ionogel layer from the mold to obtain the finished ionogel layer.

[0086] Specifically, the mass ratio of gel component to ionic salt component in the ionogel liquid is 1:1.2 to 2, and the solid mass fraction is 15% to 30%.

[0087] Specifically, the gel component is one or more of TPU, SEBS, POE, TPEE, PMMA, PBMA, polybutyl acrylate, PVDF-HFP, NBR and XSBR; the ionic salt component is one or more of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imine salt, N-butyl-N-methylpyrrolidine bisimine salt, triethylbutylammonium bisimine salt, LiTFSI and LiFSI.

[0088] It should be noted that the mass ratio of gel component to ion salt component in the ion gel liquid is 1:1.2 to 2 to ensure an excess of ion salt and to ensure continuous ion channels after swelling; when the solid mass fraction is <15%, the solution viscosity is too low, which makes it easy to flow and cause microstructure collapse during the casting process. When the solid mass fraction is greater than 30%, the viscosity is greater than 10,000 cP, making vacuum degassing difficult. Furthermore, the elastomer modulus after curing is greater than 2 MPa, resulting in decreased sensitivity in the high-pressure section.

[0089] Specifically, step S2 includes: A flexible material with insulating properties is loaded into the ink unit of a flexible electronic printer. A drawing is made on a computer, and the electronic printer deposits the flexible material onto a flexible film according to the path on the drawing, thus completing the preparation of the isolation layer.

[0090] Specifically, step S4 includes: S401: The sensor is assembled by bonding layers one by one. From top to bottom, the layers are: upper flexible electrode layer, ion sensitive layer, isolation layer, ion gel layer, middle support layer, and lower flexible electrode layer. The side of the ion sensitive layer with the first microstructure and the side of the ion gel layer with the second microstructure are set opposite to each other, and the microstructures on the upper and lower surfaces are arranged in a cross pattern. S402: Finally, add a sealing layer on both the top and bottom, and bond them together with hot-press adhesive to form a fully sealed structure.

[0091] Specifically, step S4 includes the following steps: preparing the upper flexible electrode layer by printing conductive ink on a flexible substrate; and preparing the lower flexible electrode layer using the same method.

[0092] Specifically, the fabrication of the flexible electrode layer includes: S411: Clean the surface of the flexible membrane and use a plasma cleaner to enhance its hydrophilicity; S412: Conductive ink is selected as the electrode material, and a flexible microelectronic printer is used to deposit the liquid electrode material onto the flexible film according to the drawn pattern; S413: The side of the lower flexible electrode layer that has not been printed is heated and baked to cure the flexible film, and the newly cured flexible film serves as an intermediate support layer.

[0093] Specifically, the flexible membrane in steps S411 and S413 can be a PI membrane.

[0094] Specifically, the encapsulation material fabrication in step S4 includes: S421: Cut the encapsulation material film according to the size requirements of the printer platform; S422: Perform necessary pretreatment on the cut encapsulation material film, such as cleaning and drying, to ensure that its surface is clean and free of contamination, in preparation for the subsequent bonding and encapsulation process.

[0095] Specifically, the encapsulation material film can be a PI film, and the encapsulation operation can be carried out by selecting a suitable flexible encapsulation process based on the material of the encapsulation material film.

[0096] To better illustrate the present invention, the following embodiments and comparative examples are provided:

[0097] Example 1 This embodiment discloses a capacitive flexible pressure sensor based on a double-sided hierarchical microstructure, such as... Figures 1-14 As shown, it includes: Along the thickness direction from top to bottom, it includes: Upper encapsulation layer 5a; Upper flexible electrode layer 1a; Ion-sensitive layer 2; Isolation layer 3; Ion gel layer 4; Intermediate support layer 6; Lower flexible electrode layer 1b; Lower encapsulation layer 5b; The lower surface of the upper flexible electrode layer 1a is bonded to the upper surface of the ion-sensitive layer 2 to form a first interface. The lower surface of the ion-sensitive layer 2 is provided with a first microstructure 21, and the upper surface of the ion gel layer 4 is provided with a second microstructure 41. The first microstructure 21 and the second microstructure 41 are arranged facing each other and staggered along the in-plane direction. The isolation layer 3 is a continuous closed frame. The upper surface of the isolation layer 3 is in contact with the periphery of the lower surface of the ion-sensitive layer 2, and the lower surface of the isolation layer 3 is bonded to the periphery of the upper surface of the ion gel layer 4, so that the first microstructure 21 and the second microstructure 41 maintain a non-contact air gap when there is zero pressure. The lower surface of the ion gel layer 4 is bonded to the upper surface of the lower flexible electrode layer 1b through the intermediate support layer 6, forming a second interface; The upper encapsulation layer 5a completely covers the upper surface of the upper flexible electrode layer 1a, and the lower encapsulation layer 5b completely covers the lower surface of the lower flexible electrode layer 1b; the outer edges of the upper encapsulation layer 5a and the lower encapsulation layer 5b are bonded to each other, and the ion-sensitive layer 2, the isolation layer 3, the ion gel layer 4, the intermediate support layer 6, and the sidewall of the lower flexible electrode layer 1b are completely sealed to form a fully sealed structure.

[0098] The upper flexible electrode layer 1a and the lower flexible electrode layer 1b have a thickness of 30 μm.

[0099] The upper encapsulation layer 5a and the lower encapsulation layer 5b are polyimide (PI) films, each with a thickness of 50 μm.

[0100] The encapsulation layer 6 uses a polyimide (PI) film material with a thickness of 50 μm.

[0101] The ion-sensitive layer 2 uses a 500 μm PDMS microstructure elastomer as a substrate, with a Ti3C2T coating on the surface. x T = surface functional groups –OH, –F, =O, x represents the number of surface functional groups, ranging from 1 to 2.

[0102] Two-dimensional material, the first microstructure in the ion-sensitive layer has a depth of 35 μm.

[0103] The isolation layer 3 is a silicone with a thickness of 100μm.

[0104] The ionogel layer 4 is a 3000 μm thick TPU layer, and the second microstructure in the ionogel layer has a depth of 100 μm.

[0105] The first microstructure in the ion-sensitive layer forms an angle of 65° with the plane of the ion-sensitive layer; the second microstructure in the ion gel layer forms an angle of 65° with the plane of the ion gel layer.

[0106] This embodiment also discloses a method for fabricating a capacitive flexible pressure sensor based on a double-sided hierarchical microstructure: S1: Two sets of microstructure molds with different depths and certain tilt angles are obtained through two tilting photolithography processes. One set of microstructure molds is used for molding an ion-sensitive layer with a first microstructure on one side of the surface, and the other set of microstructure molds is used for molding an ion gel layer with a second microstructure on one side of the surface. The tilt angles of the two sets of microstructure molds are matched so that the first and second microstructures are set facing each other and staggered along the in-plane direction, including: S101: A microstructure mold consisting of a silicon wafer and microstructures at a certain tilt angle to the silicon wafer is fabricated using photolithography. During exposure, a certain angle must be maintained between the silicon wafer and the incident light, so that the microstructures in the microstructure mold have a tilt angle, such as... Figure 4 As shown, to obtain a microstructure mold with a tilt angle, the silicon wafer is placed at a non-perpendicular angle to the exposure light during the exposure process, thus creating a mold with a tilt angle using photolithography. The tilted microstructure ensures that the microstructures tilt in the same direction when compressed, preventing stacking and maximizing the function of each microstructure.

[0107] S101 includes: S1011: Take a single-sided polished silicon wafer and perform air blowing, baking and ion cleaning pretreatment; S1012: After spin-coating and curing photoresist on the polished surface of a silicon wafer, the process for fabricating the microstructure mold of the ion-sensitive layer meets the following requirements: A microstructure mold with a depth of about 35 μm can be obtained by running at 500 r / min for 5 s and then at 3000 r / min for 30 s.

[0108] The fabrication process for the microstructure mold of the ionogel layer meets the following requirements: A microstructure mold with a depth of 100 μm can be obtained by running at 100 r / min for 5 s and then at 1500 r / min for 30 s. S1013: After the photoresist is attached to the mask on the silicon wafer, the angle between the silicon wafer and the incident light is controlled for exposure. In S1013, the angle between the silicon wafer and the incident light is 25°. S1014: A silicon wafer with a microstructure on its surface is obtained after development.

[0109] S102: A microstructured elastomer is prepared using a pre-made microstructured mold, cured by heating, and then peeled off. A two-dimensional material is then coated onto its surface to complete the preparation of the ion-sensitive layer, including: S1021: The prepared silicon wafer with microstructure is fixed as a mold on the spin coater. A solution of PDMS and curing agent in a 10:1 mass ratio is poured into the mold. Spin coat is performed at 100 r / min for 5 s and then at 1500 r / min for 30 s. S1022: When less than 10 4Degas for 10-30 minutes under vacuum. S1023: Dry at 60℃~70℃ for 1h~2h to complete the preparation of the ion-sensitive layer; S1024: A two-dimensional material is coated on the surface of the ion-sensitive layer, including: The ion-sensitive layer was pretreated by vacuum immersion in a 0.2 mg / ml chitosan aqueous solution for 24 h to overcome the problem of low bonding strength between the two-dimensional material and the ion-sensitive layer, which makes it easy to fall off. After vacuum immersion pretreatment, the ion-sensitive layer was dried at 50°C for 4 hours and then immersed in a 2 mg / mL two-dimensional material dispersion. After drying at 50°C, an ion-sensitive layer with a two-dimensional material coating on its surface was obtained.

[0110] S103: Pour the prepared ionogel solution into the microstructure mold. After solidification, slowly peel it off from the mold to complete the preparation of the ionogel layer, including: S1031: Thermoplastic polyurethane (TPU) is dissolved in tetrahydrofuran (THF) at a mass ratio of 1:12 and stirred at 60°C for two hours to prepare a TPU solution. 1.5 times the mass of 1-ethyl-3-methylimidazolium diimide salt ion solution is added to the liquid and stirred at 60°C for one hour to obtain an ion gel liquid. The prepared silicon wafer with microstructure is placed on a horizontal platform as a mold, and the prepared ion gel liquid is slowly poured onto the silicon wafer to completely cover the mold. S1032: Place in a fume hood at room temperature for 12 hours; S1033: Separate the cured ionogel layer from the mold to obtain the finished ionogel layer.

[0111] S2: Printing an isolation layer on the side of the ionogel layer with the second microstructure, including: Silicone rubber is loaded into the ink unit of a flexible electronic printer. A path, i.e., a 2×2cm square, is drawn on a computer. The electronic printer prints the rubber directly onto the prepared ionogel layer according to the path on the drawing. This ensures that the isolation layer and the ionogel layer do not slip relative to each other when subjected to pressure.

[0112] S3: The side of the ion-sensitive layer with the first microstructure is stacked with the side of the ion gel layer with the second microstructure facing each other, so that the first microstructure and the second microstructure are misaligned and the isolation layer is located between the ion-sensitive layer and the ion gel layer to obtain a pressure sensor preform.

[0113] S4: The upper flexible electrode layer, the pressure sensor preform, the middle support layer, and the lower flexible electrode layer are stacked sequentially and then packaged to obtain the finished flexible pressure sensor, including: S401: The sensor is assembled by bonding layers one by one. From top to bottom, the layers are: upper flexible electrode layer, ion sensitive layer, isolation layer, ion gel layer, middle support layer, and lower flexible electrode layer. The side of the ion sensitive layer with the first microstructure and the side of the ion gel layer with the second microstructure are set opposite to each other, and the microstructures on the upper and lower surfaces are arranged in a cross pattern. S402: Finally, add a sealing layer on both the top and bottom, and bond them together with hot-press adhesive to form a fully sealed structure.

[0114] The packaging material manufacturing process includes: S421: Cut the encapsulation material film according to the size requirements of the printer platform; S422: Perform necessary pretreatment on the cut encapsulation material film, such as cleaning and drying, to ensure that its surface is clean and free of contamination, in preparation for the subsequent bonding and encapsulation process.

[0115] Fabrication of flexible electrode layer: S411: Clean the surface of the flexible membrane and use a plasma cleaner to enhance its hydrophilicity; S412: Conductive ink is selected as the electrode material, and a flexible microelectronic printer is used to deposit the liquid electrode material onto the flexible film according to the drawn pattern; copper nanowires are selected as the electrode material, and a flexible microelectronic printer is used to deposit the liquid electrode material onto the flexible film according to the drawn pattern. The film is baked at 85°C for 1 hour to obtain the lower flexible electrode layer and the upper flexible electrode layer. S413: The side of the lower flexible electrode layer that has not been printed is heated and baked to cure the flexible film, and the newly cured flexible film serves as an intermediate support layer.

[0116] like Figure 1 The diagram shown is a layered schematic of the pressure sensor obtained in this embodiment.

[0117] Figure 2a A three-dimensional simulation model of the double-sided hierarchical microstructure of this invention. (See diagram below.) Figure 2a As shown, for the sake of simulation speed, only two columns of microstructures were modeled and simulated. When the pressure is low, only the tops of the microstructures make contact. As the pressure increases, the microstructures gradually tilt, and the contact area continuously increases. The height-gradient setting can improve the bandwidth and linearity of the sensor. Moreover, the structure maintains a fixed direction when tilting under force, avoiding the stacking problem that occurs when microstructures in different columns tilt.

[0118] like Figure 3 As shown in the simulation, the contact area of ​​the double-sided hierarchical microstructure designed in this invention increases continuously when it is gradually compressed.

[0119] Figure 5This is an electron microscope image of the double-sided hierarchical microstructure mold of the present invention. The sensor prepared in this embodiment has a microstructure area of ​​289.002125 mm². 2 It has 7467 microstructural units.

[0120] Figure 6 , Figure 7 The images shown are actual pictures of the ion-sensitive layer and the ion gel layer in Example 1 of this invention, both of which have microstructures on their surfaces.

[0121] Figures 8a-8b This describes the actual printing process of the isolation layer in Embodiment 1 of the present invention. The material used in this process is silicone, which has high viscosity, is not easily diffused, is suitable for printing, and has good insulation properties. The printing path is a square with a side length of 2 cm and a height of 100 micrometers.

[0122] Figure 9 A pressure testing platform for testing sensor performance, including an LCR digital bridge and an electronic universal testing machine.

[0123] Figure 10 This refers to the response time and recovery time of the capacitive flexible pressure sensor based on a double-sided hierarchical microstructure in Example 1 of this invention. For example... Figure 10 As shown, the sensor's response time and recovery time are 15ms and 25ms respectively when subjected to pressure stimulation, demonstrating a very fast response capability.

[0124] Figure 11 This describes the pressure-capacitance relationship of the capacitive flexible pressure sensor based on a double-sided hierarchical microstructure in Example 1 of this invention. Figure 11 As shown, the sensor exhibits a high pressure of 36.46 kPa when the pressure is less than 0.25 kPa. -1 It has high sensitivity, and its detection range can reach up to 250 kPa.

[0125] Figure 12 This is a pulse waveform captured when the capacitive flexible pressure sensor based on a double-sided hierarchical microstructure, as described in Example 1 of this invention, is attached to the wrist. The pressure sensor prepared in this example, when attached to the wrist, can sensitively detect minute pressure from the pulse, demonstrating its significant application potential in the medical field.

[0126] Figure 13 This is a bending-capacitance signal image collected when the capacitive flexible pressure sensor based on a double-sided hierarchical microstructure is attached to a finger joint, as shown in Example 1 of this invention. By tightly attaching the sensor prepared in this embodiment to the finger joint, guiding the finger to perform bending movements of varying degrees, the sensor can accurately capture the pressure changes caused by finger bending.

[0127] Figure 14This is a detection diagram of vocal tract vibration by a capacitive flexible pressure sensor based on a double-sided hierarchical microstructure, as shown in Example 1 of this invention. The sensor prepared in this embodiment is attached to the vocal tract, and the vocal tract vibrates by emitting the sounds "a", "b", and "c". Figure 14 As shown, the sensor can detect even minute vibrations in the vocal tract caused by sound, and the capacitive response to the same sound is basically the same, indicating that the sensor can maintain stability even under minute vibrations.

[0128] In summary, the capacitive flexible pressure sensor based on a bifacial hierarchical microstructure provided in Embodiment 1 of the present invention has high sensitivity, wide detection range, fast response, low detection limit and long-term working stability, and has great application potential in fields such as human motion monitoring, vibration and tactile perception.

[0129] Example 2 This embodiment uses the fabrication method of the capacitive flexible pressure sensor based on a bifacial hierarchical microstructure provided in Example 1. The difference from Example 1 is that the copper nanowires in step 1 are replaced with silver nanowires of the same size. Other fabrication methods are the same as in Example 1. Performance testing showed that silver nanowires were selected as the electrode material, and the sensor sensitivity was 36.46 kPa. -1 The maximum pressure measurement range is 250 kPa.

[0130] Example 3 This embodiment uses the fabrication method of the capacitive flexible pressure sensor based on a double-sided hierarchical microstructure provided in Example 1. The difference from Example 1 is that the microstructure elastomer material PDMS in steps S1 and S102 is replaced with silicone. The other fabrication methods are the same as in Example 1. Performance testing showed that silicone was selected as the microstructure elastomer material, and the sensor sensitivity was 36.38 kPa. -1 The maximum pressure range for measurement is 250 kPa.

[0131] Example 4 This embodiment uses the fabrication method of the capacitive flexible pressure sensor based on a bifacial hierarchical microstructure provided in Example 1. The difference from Example 1 is that the two-dimensional material MXene in step 3 is replaced with carbon nanotubes; the other fabrication methods are the same as in Example 1. Performance testing showed that using carbon nanotubes as a conductive coating on the microstructured elastomer resulted in a sensor sensitivity of 27.35 kPa. -1 The maximum measurement range is 250 kPa, the response time is 35 ms, and the recovery time is 25 ms.

[0132] Comparative Example 1 This comparative example prepares a single-layer microstructure capacitive flexible pressure sensor. The preparation method differs from Example 1 in that, in step 3, PDMS and curing agent are mixed at a 1:10 ratio and poured directly into a clean glass petri dish for heating and curing. The cured PDMS is then peeled off the petri dish and cut into 2×2cm squares. A layer of MXene is then coated onto the surface, following the same procedure as in Example 1, resulting in an ion-sensitive layer without microstructures. The remaining steps are the same as in Example 1, ultimately producing a single-layer microstructure capacitive flexible pressure sensor. Performance testing shows that the sensor has a sensitivity of 26.47 kPa⁻¹ and a pressure measurement range of 150 kPa. Compared to Example 1, the performance is reduced, with a 10 kPa⁻¹ decrease in sensitivity and a 100 kPa reduction in measurement range.

[0133] Comparative Example 2 This comparative example fabricates a capacitive flexible pressure sensor based on ion gel. The difference from Example 1 is that the steps for fabricating the ion-sensitive layer and isolation layer are skipped; the remaining steps are the same as in Example 1. The resulting capacitive flexible pressure sensor consists of two electrode layers and an ion gel layer, forming a classic "sandwich" structure, a common structure for existing capacitive sensors. Performance testing showed that the sensor has a sensitivity of 20.16 kPa⁻¹, a pressure measurement range of 145 kPa, and response and recovery times of 21 ms and 60 ms, respectively. Compared to Example 1, all performance aspects are significantly reduced.

[0134] The results show: The pressure sensor prepared in this embodiment of the invention has a sensitivity of 27 kPa⁻¹~36 kPa⁻¹, a range of 0~250 kPa, a response time of 15~35 ms, a recovery time of ≤25 ms, a drift of <5% after 5000 cycles, and a minimum detection limit of 0.8 Pa. Compared with the prior art, the sensitivity and range are significantly improved, while the response time and recovery time are significantly reduced.

[0135] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A capacitive flexible pressure sensor based on a double-sided hierarchical microstructure, characterized in that, From top to bottom along the thickness direction, the layers are: upper encapsulation layer, upper flexible electrode layer, ion-sensitive layer, isolation layer, ion gel layer, middle support layer, lower flexible electrode layer, and lower encapsulation layer. The lower surface of the upper flexible electrode layer is bonded to the upper surface of the ion-sensitive layer to form a first interface; The lower surface of the ion-sensitive layer is provided with a first microstructure, and the upper surface of the ion gel layer is provided with a second microstructure. The first microstructure and the second microstructure are arranged facing each other and staggered along the in-plane direction. The isolation layer is a continuous closed frame. The upper surface of the isolation layer is in contact with the periphery of the lower surface of the ion-sensitive layer, and the lower surface of the isolation layer is bonded to the periphery of the upper surface of the ion gel layer, so that the first microstructure and the second microstructure maintain a non-contact air gap under zero pressure. The lower surface of the ion gel layer is bonded to the upper surface of the lower flexible electrode layer through an intermediate support layer to form a second interface; The upper encapsulation layer completely covers the upper surface of the upper flexible electrode layer, and the lower encapsulation layer completely covers the lower surface of the lower flexible electrode layer; the outer edges of the upper and lower encapsulation layers are bonded to each other, and the ion-sensitive layer, the isolation layer, the ion gel layer, the intermediate support layer, and the sidewalls of the lower flexible electrode layer are completely sealed to form a fully sealed structure.

2. The capacitive flexible pressure sensor based on a double-sided hierarchical microstructure according to claim 1, characterized in that, The depth of the first microstructure in the ion-sensitive layer is 30 μm to 40 μm; the depth of the second microstructure in the ion gel layer is 80 μm to 120 μm.

3. The capacitive flexible pressure sensor based on a double-sided hierarchical microstructure according to claim 1, characterized in that, The angle between the first microstructure in the ion-sensitive layer and the plane of the ion-sensitive layer is 60°~70°; the angle between the second microstructure in the ion gel layer and the plane of the ion gel layer is 60°~70°.

4. The capacitive flexible pressure sensor based on a bifacial hierarchical microstructure according to any one of claims 1-3, characterized in that, The ion-sensitive layer uses a microstructured elastomer as a substrate and a two-dimensional material is coated on its surface.

5. The capacitive flexible pressure sensor based on a double-sided hierarchical microstructure according to claim 4, characterized in that, The two-dimensional material is one or more of the following: two-dimensional transition metal carbon / nitrides, graphene and its derivatives, two-dimensional transition metal sulfides, two-dimensional metal oxides, or carbon nanotube films.

6. A method for fabricating a capacitive flexible pressure sensor based on a double-sided hierarchical microstructure, characterized in that, The method for fabricating a capacitive flexible pressure sensor based on a bifacial hierarchical microstructure as described in any one of claims 1-5 comprises the following steps: S1: Two sets of microstructure molds with different depths and a certain tilt angle are obtained by two tilting photolithography. One set of microstructure molds is used to prepare an ion-sensitive layer with a first microstructure on one side of the surface. The other set of microstructure molds is used to prepare an ion gel layer with a second microstructure on one side of the surface. The tilt angles of the two sets of microstructure molds are matched so that the first microstructure and the second microstructure are set facing each other and staggered along the in-plane direction. S2: Print an isolation layer on the side of the ionogel layer that has the second microstructure; S3: The side of the ion-sensitive layer with the first microstructure is stacked with the side of the ion gel layer with the second microstructure facing each other, so that the first microstructure and the second microstructure are misaligned and the isolation layer is located between the ion-sensitive layer and the ion gel layer to obtain a pressure sensor preform. S4: The upper flexible electrode layer, the pressure sensor preform, the middle support layer, and the lower flexible electrode layer are stacked in sequence and then packaged to obtain the finished flexible pressure sensor.

7. The molding method for a capacitive flexible pressure sensor based on a double-sided hierarchical microstructure according to claim 6, characterized in that, Step S1 includes: S101: A microstructure mold consisting of a silicon wafer and microstructures at a certain tilt angle to the silicon wafer is fabricated using photolithography. During the exposure process, a certain angle must be maintained between the silicon wafer and the incident light so that the microstructures in the microstructure mold have a tilt angle. S102: A microstructured elastomer is prepared using a pre-made microstructured mold, cured by heating, and then peeled off to complete the preparation of the ion-sensitive layer; S103: Prepare an ion gel solution by pouring the ion gel solution into a microstructure mold and allowing it to solidify before peeling it off from the mold to complete the preparation of the ion gel layer.

8. The molding method for a capacitive flexible pressure sensor based on a double-sided hierarchical microstructure according to claim 7, characterized in that, Step S101 includes: adjusting the microstructure depth in the microstructure mold by adjusting the rotation speed and time of the spin coater.

9. The molding method for a capacitive flexible pressure sensor based on a double-sided hierarchical microstructure according to claim 7, characterized in that, In step S101, the angle between the silicon wafer and the incident light is 20°~30°.

10. The molding method of the capacitive flexible pressure sensor based on a double-sided hierarchical microstructure according to any one of claims 7-9, characterized in that, Step S102 further includes: coating a two-dimensional material onto the surface of the ion-sensitive layer.

Images