Ionic gel flexible pressure film sensing array and preparation method thereof

Abstract

The invention discloses an ionic gel flexible pressure film sensing array and a preparation method thereof. The sensing array comprises two layers of patterned flexible electrodes, an ionic gel unit array containing a surface microstructure and a patterned isolation layer. The ionic gel layer and the isolation layer are located on the same plane, each ionic gel unit is surrounded by the isolation layer unit structure, the two layers of electrodes respectively cover the upper side and the lower side, the ionic gel is in contact with an electrode conductive region, and the isolation layer is in contact with a non-conductive region. The preparation method comprises the following steps: performing laser etching and patterning processing on the flexible electrode; preparing a mask with a hollow pattern and covering the mask to the first electrode; imprinting on the polymer film to prepare a microstructure mold; dropwise adding liquid ionic gel into the mold, and pressing and curing the first electrode covered with the mask to form an ionic gel unit array; and bonding the isolation layer and the two layers of electrodes. The preparation method is low in cost, simple, flexible, thin in device thickness, wide in measuring range, high in sensitivity and signal-to-noise ratio, resistant to sensitive layer crosstalk and suitable for various pressure detection scenes.

Description

TECHNICAL FIELD

[0001] The present application relates to a pressure sensor, in particular to an ionic gel flexible pressure film sensing array and a preparation method thereof. BACKGROUND

[0002] With the continuous development of wearable devices, robot skin and other technologies, the technology of making sensors into flexible and film-shaped forms to adapt to various measurement environments has attracted widespread attention. Pressure is an important physical quantity of sensing measurement, and pressure film sensors have a wide range of applications in blood pressure monitoring, mechanical arm force feedback, electronic touch screen pressure sensing, seat pressure distribution and other fields. Current pressure film sensors are often based on the following principles, such as resistive pressure sensors using piezoresistive effect, piezoelectric force sensors using piezoelectric effect, and capacitive pressure sensors using changes in electrode distance caused by pressure. These methods can convert the measured force into the deformation of the device to change the resistance / charge / capacitance of the device, and through the design of the circuit, the measured pressure value can be obtained by comparing the force-resistance / current / capacitance curve. However, current thin film pressure sensors generally have short measurement range and low resolution, and there is a need to balance the pressure measurement range, film thickness and sensitivity. In addition, in the preparation process of the pressure film array, the preparation of the sensitive layer often uses methods such as magnetron sputtering, lithography and etching, screen printing, inkjet printing, and laser direct writing. These methods require high equipment costs and some require special molds or are difficult to achieve the preparation of the surface microstructure of the sensitive layer, which is not conducive to the production of multi-application scenario and multi-form sensors, and lacks flexibility and low cost.

[0003] It should be noted that the information disclosed in the above background section is only for understanding the background of the present application, and therefore can include information that does not constitute prior art known to those of ordinary skill in the art. SUMMARY

[0004] The main purpose of the present application is to overcome the defects in the above background art, and to provide an ionic gel flexible pressure film sensing array and a preparation method thereof.

[0005] To achieve the above purpose, the present application adopts the following technical solutions:

[0006] An ionic gel flexible pressure film sensing array, comprising:

[0007] Two patterned flexible electrodes;

[0008] An ionic gel layer composed of an array of ionic gel units with surface microstructure;

[0009] A separation layer composed of a non-conductive flexible material with a patterned unit structure array;

[0010] The ion gel layer and the isolation layer are located in the same plane, each ion gel unit is surrounded by the patterned unit structure of the isolation layer, and the two layers of patterned flexible electrodes are respectively covered on the upper and lower sides of the ion gel layer and the isolation layer.

[0011] Further, the conductive areas of the two layers of flexible electrodes are arranged in a transverse and longitudinal direction perpendicular to each other to form a sensing array unit; the flexible electrode comprises a substrate and a surface conductive layer, and the conductive layer material comprises silver nanowires (AgNWs), indium tin oxide (ITO), or poly 3,4-ethylenedioxythiophene (PEDOT).

[0012] Further, the surface microstructure of the ion gel layer is formed by sandpaper embossing a fluorinated ethylene propylene copolymer (FEP) film, and the sandpaper mesh number can be selected from at least two combinations of 400 mesh to 1200 mesh, but is not limited to the above mesh number range.

[0013] Further, the thickness of the isolation layer is greater than the thickness of the ion gel layer, the inner diameter of the isolation layer is smaller than the size of the conductive area of the flexible electrode and greater than the size of the ion gel unit, and the material of the isolation layer comprises polydimethylsiloxane (PDMS) or double-sided adhesive tape, and the elastic modulus thereof can be adjusted; the isolation layer and the flexible electrode are bonded by a surface treatment agent or a flexible adhesive.

[0014] Further, the surface microstructure of the ion gel layer is a surface microstructure with hierarchical scales.

[0015] A preparation method of an ion gel flexible pressure film sensing array, comprising the following steps:

[0016] S1. The two layers of flexible electrodes are respectively patterned by laser etching;

[0017] S2. A mask with a hollow pattern is prepared and covered on the conductive surface of the first flexible electrode;

[0018] S3. A microstructure mold is prepared by embossing a pressure-embossable polymer film;

[0019] S4. Liquid ion gel is added to the mold, and the first flexible electrode covered with the mask is pressed and solidified after curing to realize in-situ patterning and microstructure forming of the ion gel, thereby forming an ion gel unit array with a surface microstructure;

[0020] S5. Removing the mold and the mask, bonding the patterned isolation layer with the first flexible electrode with the shaped ionogel and the other layer of the second flexible electrode, so that each ionogel unit is surrounded by the patterned isolation layer and in contact with the conductive area of the first flexible electrode and the second flexible electrode.

[0021] Further, the mask in step S2 is PET single-sided adhesive tape, and the size of the hollowed-out pattern is larger than the size of the conductive area of the flexible electrode; the curing method in step S4 is ultraviolet irradiation or heating, and the ionogel forms irreversible adhesion with the first flexible electrode during curing.

[0022] Further, in step S3, a microstructure mold is prepared by pressing on the polymer film using a composite sandpaper, and the composite sandpaper comprises a combination of at least two types of sandpaper, and a scale-graded surface microstructure is formed on the microstructure mold by pressing different types of sandpaper in sequence.

[0023] Further, in step S4, the thickness of the ionogel is controlled by the thickness of the mask, and the thickness of the mask is 0.08mm to 0.5mm.

[0024] Further, in step S5, the isolation layer is formed by blade coating, spin coating or cutting a pre-made film, and the surface is treated with a modifier to improve adhesion; the thickness of the isolation layer is slightly higher than the thickness of the gel, and the thickness of the isolation layer can be 0.2mm to 1mm, and the inner circle size is 0.2mm to 0.4mm larger than the ionogel unit according to the thickness of the mask.

[0025] The present application has the following advantages:

[0026] The present application provides a simple and low-cost ionogel wide-range flexible pressure film sensor array and its preparation process, which has significant technical advantages and application value. The flexible pressure film sensor array has high sensitivity, high signal-to-noise ratio and good linearity, can realize wide-range pressure measurement, has thin thickness, small volume, good flexibility and portability, and can effectively resist sensitive layer crosstalk; at the same time, it has strong stability in different application scenarios, is easy to adjust flexibly according to requirements, can quickly obtain contact pressure value and pressure action position, and has excellent overall performance. The process equipment has low cost, high preparation flexibility and multiple adjustable parameters, and the film sensor array prepared thereby has the characteristics of thin thickness, wide range, high signal-to-noise ratio and resistance to sensitive layer crosstalk.

[0027] In the process design, the patterning and thickness control of the sensitive layer are realized by selecting a single-sided adhesive mask, which can directly complete the in-situ curing of the ion gel sensitive layer on the patterned electrode surface without transfer steps, effectively avoiding the damage risk of the ion gel thin layer in the traditional process when it is cured and then transferred. At the same time, the surface microstructure is made by using different mesh sandpaper to imprint FEP film as a mold, which can form a hierarchical structure. Compared with using only one mesh sandpaper, it can provide more contact area change in the later stage of large pressure, thereby improving the sensitivity.

[0028] To achieve the goals of small thickness, large range and high sensitivity of the pressure film sensor, the present application selects ion gel as the device sensitive layer, which has a double-layer capacitance with high signal-to-noise ratio when in contact with the electrode, and the sensitivity can be further improved by reasonable design of the surface microstructure. The designed preparation process can flexibly cure the ion gel with surface microstructure in-situ on the patterned electrode area, and cooperate with the isolation layer that can withstand large pressure, to realize the simple and low-cost controllable preparation of thickness and range. In addition, the electrode size, mask thickness, isolation layer thickness, sandpaper mesh and other structural parameters of the sensor can be flexibly adjusted according to the measurement requirements and application scenarios - the sensitivity is related to the mesh of the imprinted sandpaper, and the range is related to the area ratio of the isolation layer and the gel, and the elastic modulus of the isolation layer. By adjusting these parameters, different range requirements can be met. During the curing process, if light curing is used, only one side of the flexible electrode can be transparent; if thermal curing is used, one side of the flexible electrode can withstand the thermal curing temperature, and the other side of the flexible electrode can be replaced by other conductive films or conductive fabrics according to the application requirements, further improving the adaptability of the process.

[0029] Overall, the present application realizes the in-situ curing of ion gel on flexible conductive film, which is highly flexible and can replace structural materials flexibly in the whole process according to measurement requirements and application scenarios. The final pressure film sensor has high sensitivity, high signal-to-noise ratio and small volume. Compared with traditional technology, the present application provides a flexible film sensor with thin thickness, wide range, high signal-to-noise ratio and anti-sensitive layer crosstalk, and a process for flexibly making surface microstructure, which provides a solution for balancing the relationship between sensitivity, linearity and range of flexible film sensor based on ion gel under the condition of limited thickness; at the same time, the low-cost in-situ patterning ion gel process of the present application solves the damage problem caused by transfer in the traditional process. In addition, the present application can realize a flexible patterning ion gel sensor array with thin size and low cost, which has good linearity, flexibility and portability, can quickly obtain contact pressure value, has good stability in different application scenarios, and is easy to adjust, and has wide application prospect.

[0030] The scheme of the present application has good stability and is easy to adjust flexibly in different application scenarios, and has wide application prospect.

[0031] Other benefits of embodiments of the present application will be described further below. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a structural schematic diagram of an embodiment of the present application.

[0033] Figure 1 is a structural schematic diagram of an ion gel-based wide-range flexible pressure thin film sensor array of an embodiment of the present application;

[0034] Figure 2 is a sectional view of a sensor unit in an embodiment of the present application;

[0035] Figure 3 is a process flow diagram for preparing an ion gel-based wide-range flexible pressure thin film sensor array in an embodiment of the present application;

[0036] Figure 4 is a structural schematic diagram of a device unit in a mask curing process in an embodiment of the present application;

[0037] Figure 5 is a sensitivity curve of an ion gel thin film sensor unit in an embodiment of the present application, which is calibrated by imprinting with high-mesh sandpaper;

[0038] Figure 6 is a sensitivity curve of an ion gel thin film sensor unit in an embodiment of the present application, which is calibrated by imprinting with low-mesh sandpaper.

[0039] Figure 7 shows electron microscope images of molds imprinted with 1200-mesh, 800-mesh and 400-mesh sandpaper in different orders in an embodiment of the present application: (a) from low to high; and (b) from high to low.

[0040] Figure 8 shows a repeatability test response curve in an embodiment of the present application, which shows the consistency of the capacitance response in a cyclic pressure test.

[0041] Figure 9 shows a sensor unit temperature drift test diagram in an embodiment of the present application: (a) a schematic of a test device; and (b) a temperature drift test result. DETAILED DESCRIPTION

[0042] The embodiments of the present application are described in detail below. It should be emphasized that the following description is only exemplary and is not intended to limit the scope of the present application and its applications.

[0043] It is to be noted that when an element is referred to as being "fixed" or "set" on another element, it can be directly on the other element or indirectly on the other element. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or indirectly connected to the other element. In addition, the connection can be for fixing or for coupling or for communication.

[0044] It is to be understood that the terms "length", "width", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate directions or positions based on the directions or positions shown in the drawings, and are used for the purpose of facilitating the description of the embodiments of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be construed as limiting the present application.

[0045] In addition, the terms "first", "second", "third", etc. are used only for descriptive purposes and cannot be construed as indicating or implying relative importance or an implied indication of the number of technical features indicated. Therefore, the features defined as "first", "second", etc. can explicitly or implicitly include one or more of the features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0046] To realize the characteristics of small thickness, large range, high sensitivity and the like of the pressure thin film sensor, the present application selects ion gel as the device sensitive layer, the double-layer capacitance formed by the contact of the ion gel with the electrode has the characteristics of high signal-to-noise ratio, and in combination with the reasonable design of the surface microstructure, high sensitivity can be realized, the designed preparation process can flexibly realize in-situ solidification of the ion gel with the surface microstructure in the electrode patterning area, and in combination with the isolation layer capable of bearing large pressure, simple and low-cost controllable preparation of thickness and range is realized.

[0047] Referring to Figure 1 and Figure 2 , the embodiment of the present application provides an ion gel flexible pressure thin film sensing array, which comprises: two layers of patterned flexible electrodes 1, 3; an ion gel layer composed of an ion gel 2 unit array with a surface microstructure; an isolation layer 4 composed of a non-conductive flexible material and having a patterned unit structure array; wherein the ion gel layer and the isolation layer 4 are located in the same plane, each ion gel 2 unit is surrounded by the patterned unit structure of the isolation layer 4, and the two layers of patterned flexible electrodes are respectively covered on the upper and lower sides of the ion gel layer and the isolation layer 4; the ion gel layer is in contact with the conductive areas of the two layers of flexible electrodes 1, 3 on both sides, the isolation layer 4 is in contact with the non-conductive areas of the two layers of flexible electrodes; the contact area of the ion gel layer with the flexible electrodes 1, 3 changes under the action of pressure, causing a change in capacitance.

[0048] Referring to Figure 1 In some embodiments, the conductive regions of the two flexible electrodes 1, 3 are arranged in a perpendicular transverse and longitudinal direction, forming a sensing array unit; the flexible electrodes comprise a substrate and a surface conductive layer, and the conductive layer material comprises silver nanowires (AgNWs), indium tin oxide (ITO), or poly 3,4-ethylenedioxythiophene (PEDOT).

[0049] In some embodiments, the surface microstructure of the ionogel layer is formed by sandpaper embossing a fluorinated ethylene propylene (FEP) film, and the sandpaper grit includes at least two combinations of 400 grit to 1200 grit.

[0050] In some embodiments, the isolation layer 4 has a thickness greater than that of the ionogel layer 2, and the inner diameter of the isolation layer 4 is smaller than the size of the conductive region of the flexible electrode and greater than the size of the ionogel 2 unit; the material of the isolation layer 4 comprises polydimethylsiloxane (PDMS) or double-sided tape, and the elastic modulus of the material can be adjusted; the isolation layer 4 and the flexible electrode are bonded by a surface treatment agent or a flexible adhesive.

[0051] Referring to Figure 2 In some embodiments, the surface microstructure of the ionogel layer is a surface microstructure with hierarchical scales.

[0052] Referring to Figure 3 and Figure 4 The embodiments of the present application also provide a preparation method of an ionogel flexible pressure film sensing array, comprising:

[0053] Step S1. Perform patterned processing on the two flexible electrodes 1, 3 by laser etching 5;

[0054] Step S2. Prepare a mask 6 with a hollow pattern and cover it to the conductive surface of the first flexible electrode 1;

[0055] Step S3. Prepare a microstructure mold 7 by embossing a polymer film (such as FEP) that can be embossed;

[0056] Step S4. Add liquid ionogel to the mold 7, cover the first flexible electrode with the mask 6, and then solidify after pressing, to realize in-situ patterning and microstructure forming of the ionogel, and form an ionogel 2 unit array with a surface microstructure;

[0057] Step S5. Remove the mold 7 and the mask 6, and bond the patterned isolation layer 4 with the first flexible electrode with the formed ionogel 2 and the second flexible electrode, so that each ionogel 2 unit is surrounded by the patterned isolation layer 4 and in contact with the conductive regions of the first flexible electrode and the second flexible electrode.

[0058] In some embodiments, the mask 6 in step S2 is a PET single-sided adhesive tape with a hollow pattern whose size is larger than that of the conductive area of the flexible electrode; and the curing method in step S4 is ultraviolet irradiation or heating, and the ionogel 2 and the first flexible electrode 1 form irreversible adhesion during curing.

[0059] In some embodiments, in step S3, a microstructure mold 7 is prepared by pressing a composite sandpaper on the polymer film, wherein the composite sandpaper comprises a combination of sandpapers with at least two mesh sizes, and a scale-graded surface microstructure is formed on the microstructure mold 7 by pressing sandpapers with different mesh sizes in sequence.

[0060] In some embodiments, the thickness of the ionogel 2 in step S4 is controlled by the thickness of the mask 6, and the thickness of the mask 6 is 0.08 mm to 0.5 mm.

[0061] In some embodiments, the isolation layer 4 in step S5 is formed by blade coating, spin coating or cutting a pre-made film, and the surface of the isolation layer 4 is treated with a modifier to improve adhesion; the thickness of the isolation layer 4 is 0.2 mm to 1 mm, and the inner circle size of the isolation layer 4 is 0.2 mm to 0.4 mm larger than that of the ionogel 2 unit.

[0062] The ionogel-based wide-range flexible pressure film sensor array according to the embodiments of the present application is composed of a three-layer structure, including two flexible electrodes 1, 3, an ionogel 2 and an isolation layer 4, the conductive surface of the flexible electrodes is in contact with the ionogel 2, the ionogel 2 and the isolation layer 4 are located in the same plane, the ionogel 2 is surrounded by the isolation layer 4, and the two are sandwiched by the upper and lower flexible electrodes 1, 3. One layer of flexible electrode can be fixed on the surface of the application scene, such as the position of mechanical arm, clothes, foot pad, skin, etc., by pasting or other methods, and the measured pressure is applied to the other layer of flexible electrode. The deformation caused by the measured pressure acting on the electrode changes the contact area between the flexible electrodes 1, 3 and the ionogel 2, thereby affecting the capacitance value generated between the ionogel 2 and the flexible electrodes 1, 3. The value of the measured pressure can be obtained by comparing the capacitance-stress calibration curve. In addition, the position of the measured pressure acting on the flexible electrode can be determined by comparing the arrangement of the output capacitance signals of the sensor array.

[0063] In further embodiments:

[0064] The flexible electrodes 1, 3 are thin films with conductive surfaces, for example, polyethylene terephthalate (PET) material as a substrate surface adhering silver nanowires (AgNWs) conductive film.

[0065] The flexible electrode 1, 3 is a patternable conductive film, which can be divided into conductive regions and non-conductive regions by a laser etching process, the two layers have the same size, and the conductive patterns are arranged in horizontal and vertical directions respectively.

[0066] The polymer micromolecule of the ionic gel 2 is in a liquid state, and the flowability is not limited, and the ionic gel 2 can be polymerized from a liquid state to a solid state by a light-curing or heat-curing method.

[0067] The ionic gel 2 has a microstructure on the surface, which has the same shape and arrangement position as the patterned conductive region of the flexible electrode 1, 3, and the upper and lower sides of the ionic gel 2 are in contact with the conductive regions of the flexible electrode after patterning.

[0068] The isolation layer 4 is a non-conductive flexible material, which can be, for example, an elastic silica gel material or a double-sided adhesive material.

[0069] The ionic gel 2 is surrounded by the isolation layer 4, and the isolation layer 4 is also subjected to a patterning process, which has the same shape and arrangement position as the non-conductive region of the flexible electrode 1, 3, and the outer ring is slightly smaller than the flexible electrode, and the inner ring of each unit in the array is slightly larger than the ionic gel 2 in each unit, so as to provide a deformation space for the ionic gel 2 under the measured pressure.

[0070] The thickness of the ionic gel 2 is slightly lower than the thickness of the isolation layer 4, and the thickness of the isolation layer 4 and the thickness of the two electrodes determine the thickness of the entire thin film sensor.

[0071] The isolation layer 4 can be adhered to the flexible electrode after surface treatment.

[0072] The ionic gel 2 can be adhered to the flexible electrode during the curing process.

[0073] The microstructure on the surface of the ionic gel 2 adopts an irregular structure of sandpaper, and the parameters such as the particle density and particle size of the sandpaper can be adjusted according to the measurement needs.

[0074] In the present application, the microstructure on the surface of the ionic gel 2 can realize the adjustment of the sensitivity of the device by affecting the contact area change rule of the ionic gel 2 and the flexible electrode 1, 3, and the principle is as follows:

[0075] The circuit model of the entire sensor is constructed, the contact position of the ionic gel and the flexible electrode is simplified as a capacitor C1 and a capacitor C2, and the ionic gel itself is simplified as a resistor R e in series with a capacitor C3, and the non-contact part of the ionic gel and the flexible electrode is simplified as a capacitor C0, and for a sensing unit, the calculation formula of the equivalent capacitance C s is as follows:

[0076]

[0077] The above capacitances can be simplified as parallel plate capacitances, and the three capacitances can be represented as:

[0078]

[0079] wherein ε0 is the dielectric constant of air, ε e is the relative dielectric constant of the ionogel, S1 is the area of the flexible electrode in contact with the surface microstructure of the ionogel, S2 is the area of the flexible electrode not in contact with the ionogel but with an air layer, the sum of the two areas is the total area S of the flexible electrode, d s is the distance between the two layers of flexible electrodes (also the thickness of the isolation layer), δ e is the distance between the double electric layer formed by the ionogel and the flexible electrode.

[0080] Based on the relationship S2 = S-S1, f→1, d s >>δ e , the equivalent capacitance formula can be simplified as:

[0081]

[0082] wherein only f is a variable, and adjusting the surface microstructure of the ionogel to change the contact area change rate of the flexible electrode under the action of the force to be measured can adjust the sensitivity of the device.

[0083] The surface microstructure of the ionogel is formed by a plurality of sandpapers of different mesh numbers, and the types of sandpaper include but are not limited to silicon carbide sandpaper, diamond sandpaper, etc., and the number of different mesh numbers is not limited. Under a certain pressure, a fluorinated ethylene propylene copolymer (FEP) film is embossed, and a mold is formed.

[0084] The thickness of the ionogel is related to the height of the mask in the preparation process, and the mask material can be polyethylene terephthalate material or similar film tape.

[0085] The ion migration in the ionogel is different from that of the liquid electrolyte. For the sensor, the change of the measurement frequency will affect the sensitivity of the device, and it is recommended that the measurement frequency does not exceed 1 kHz.

[0086] Based on the capacitance-stress change curve calibrated by the sensor and the actual test capacitance signal, the measured pressure value is obtained.

[0087] The specific embodiments of the present application are further described below.

[0088] Reference is made to Figure 1 and Figure 2This invention provides a wide-range flexible pressure film sensing array based on ion gel, comprising upper and lower flexible electrodes 1 and 3, an ion gel 2 with surface microstructure, and a patterned isolation layer 4. The ion gel 2 and the isolation layer 4 are on the same plane, and each ion gel 2 unit is surrounded by the isolation layer 4. The side of the ion gel 2 without microstructure is in complete contact and adhesion to the patterned conductive area of ​​the flexible electrode 3, and the side of the ion gel 2 with microstructure is in partial contact with the conductive area of ​​the flexible electrode 1. The isolation layer 4 is in contact and adhered to both the upper and lower sides between the flexible electrodes 1 and 3. The specific process flow of the patterning and contact bonding method of the components will be further described below.

[0089] See Figure 3 The process flow shown in the figure is adopted in the embodiment of the present invention. Figure 3 The flexible electrode 1 described in (a) is subjected to laser etching 5 to ablate the conductive material (such as the ITO coating on the surface of the ITO / PET film, the PEDOT coating on the surface of the PEDOT / PET film, etc.) along the designed patterned trajectory to obtain a patterned electrode. Figure 3 The flexible electrode 7 described in (d) is also prepared by this process. Figure 3 The mask 6 described in (b) is patterned using laser cutting technology. The mask 6 is made of thin single-sided adhesive and can be made of various materials such as PET and PI. The light transmittance is not limited, and the thickness is related to the thickness requirements of the ion gel 2 required by the design. Figure 3 In (c), the mask 6 is aligned and attached to the surface of the flexible electrode 1. The conductive area of ​​the ion gel 2 that needs to be cured is not covered by the mask 6. The mold 7 is formed by pressing sandpaper of different mesh sizes onto the FEP film under a certain pressure. A liquid ion gel polymer small molecule solution is dropped onto its structural surface. The flexible electrode 1 and the mask 6 are pressed flat onto the mold 7. The mold is then irradiated for a certain time under ultraviolet light that can catalyze the curing of the ion gel 2 liquid. Figure 3 In step (d), the flexible electrode 1, after being peeled off from the mask 6, and the ion gel 2 with surface microstructures after molding, adhere tightly during the curing process, thus achieving the patterning of the ion gel 2. (See also...) Figure 4 The structure of the device unit in the mask 6 curing process is given. Figure 4 (a) and (b) show the flexible electrode 1 and the mask 6 obtained after the above patterning, respectively. To ensure that the conductive and non-conductive regions of the flexible electrode 1 are separated without being cut off, two patterns can be ablated to ensure separation. The inner circle of the ablated pattern is slightly smaller than the inner circle of the patterned mask 6, and the outer circle of the ablated pattern is slightly larger than the inner circle of the patterned mask 6, so as to ensure that the area left for the ion gel 2 to solidify can completely cover the surface of the conductive region. Figure 4The ion gel 2 described in (c) is cured between the surface of the flexible electrode 1 not covered by the mask 6 and the mold 7. Figure 4 In step (d), the mold 7 and the mask 6 are removed. At the junction of the inner ring of the mask 6 and the ion gel 2, stress concentration occurs due to the uneven thickness of the ion gel 2, which can easily break and separate, thereby obtaining a patterned ion gel 2 attached to the surface of the flexible electrode 1. Figure 3 The isolation layer 4 can be obtained as an elastic film of the designed thickness by methods such as scraping, spin coating, or purchasing commercially available finished products. The material used is a non-conductive elastomer such as polydimethylsiloxane (PDMS), and the pattern is achieved by cutting with a tool or other cutting methods. A surface treatment agent is applied to the surface of the isolation layer 4 to bond it to the flexible electrodes 1 and 7, ultimately obtaining the ion gel 2 pressure film sensing array device.

[0090] In a preferred embodiment, the ionogel 2 is a flexible photocurable material or a flexible thermocurable material, which is stretchable after curing, and its small molecules before polymerization are highly fluid liquid substances.

[0091] In a preferred embodiment, the two flexible electrodes have comparable areas, the conductive regions are positioned opposite each other, the ion gel 2 completely covers the conductive regions, and the area of ​​the non-conductive regions is comparable to the area of ​​the isolation layer 4.

[0092] In a preferred embodiment, the measured pressure range is smaller than the area covered by the ion gel 2. The range of the measured pressure is related to factors such as the material of the ion gel 2, the surface microstructure of the ion gel 2, the material of the isolation layer 4, the thickness of the isolation layer 4, and the area ratio between the ion gel 2 and the isolation layer 4. Preferably, the thickness of the ion gel 2 is slightly smaller than the thickness of the isolation layer 4, and the area of ​​the ion gel 2 is larger than the area of ​​the isolation layer 4. The adhesion between the isolation layer 4 and the two flexible electrodes can rely on the surface treatment of the isolation layer 4 or a flexible adhesive such as acrylic adhesive, which is not airtight. Based on the simple and low-cost ion gel 2 wide-range flexible pressure film sensor array fabrication process mentioned above, measurements in environments such as underwater can be achieved by vapor deposition of Pyrelin material, replacing the flexible electrode substrate with a thermoplastic polyurethane (TPU) film, or by hot-pressing TPU tape around the perimeter.

[0093] Example 1

[0094] A flexible electrode was selected using an indium tin oxide (ITO) thin film sputtered onto a PET substrate. The overall size of the conductive film was 20mm × 80mm × 0.1mm. After infrared laser etching, a square area with an effective conductive region of 10mm × 10mm and a rectangular area of ​​4mm × 60mm were used as wires for wiring. A 0.18mm thick PET single-sided adhesive mask was used, and the cut-out portion for curing the ionogel was 10.2mm × 10.2mm, which was then attached to the conductive side of the flexible electrode. A composite sandpaper structure mold was obtained by sequentially imprinting 1200-grit, 800-grit, and 400-grit sandpaper onto a 0.08mm thick FEP film. The ionogel for the sensitive layer was poly(1-butyl-3-methylimidazolium-3-methacrylate sulfonyl propionate-comethyl methacrylate) (P([BMIM][SPA]-co-MA)), a UV-curable material. Before polymerization, the small molecules were highly fluid liquids. The sample was dropped onto a composite sandpaper mold, pressed firmly with a flexible electrode covered with a mask, and irradiated under ultraviolet light for 30 minutes before the mask was removed. A 10.4mm × 10.4mm × 1mm inner ring of PET double-sided adhesive was cut using a laser cutter to serve as an insulating layer and to bond the upper and lower flexible electrodes. The final device was obtained by bonding these layers one by one.

[0095] At a measurement frequency of 1 kHz and a measurement voltage of 1 V, the sensitivity curve of the device is obtained as follows: Figure 5 High-mesh sandpaper particles have small diameters, resulting in a dense and small microstructure on the surface of the ionogel, making it easy to reach contact area saturation. Furthermore, the PET material used for the isolation layer is relatively hard and difficult to compress. While this can expand the pressure-bearing range to some extent, it has a greater impact on sensitivity; within a stress range of 0-200 kPa, the sensitivity is only 0.1274 kPa. -1 The sensitivity drops even further after 200 kPa, reaching only 0.00578 kPa. -1 .

[0096] Example 2

[0097] A poly(3,4-ethylenedioxythiophene) (PEDOT) film coated on a PET substrate was selected as the flexible electrode. The entire conductive film measures 78.5 mm × 78.5 mm × 0.05 mm. After infrared laser etching, the conductive area was divided into 10 × 10 units, each unit having an effective conductive area of ​​3 mm × 3 mm square. Each conductive unit is connected to each column by a 2 mm × 0.6 mm rectangular area (there is no conductivity between rows). A 0.08 mm thick PET single-sided adhesive mask was used, with a 3.2 mm × 3.2 mm cutout for curing the ionogel, which was then adhered to the conductive side of the flexible electrode. A composite sandpaper structure mold was obtained by sequentially imprinting 400-grit and 240-grit sandpaper onto the 0.08 mm thick FEP film. The ionogel for the sensitive layer was selected as poly(1-butyl-3-methylimidazolium-3-methacrylate sulfonyl propionate-comethyl methacrylate) (P([BMIM][SPA]-co-MA)), a UV-curable material. Before polymerization, the small molecules are highly fluid liquids. It was dropped onto a composite sandpaper mold, pressed firmly with a flexible electrode covered with a mask, and irradiated under UV light for 30 minutes before the mask was removed. A commercially available 0.2mm thick PDMS film was used as the isolation layer, cut into a grid structure with the cutouts aligned with the patterned electrode positions. Each unit had an internal dimension of 3.4mm × 3.4mm, slightly larger than the side length of the ionogel in each unit. A silicone surface modifier was coated onto the PDMS film surface to improve the adhesion between the PDMS and the PEDOT / PET electrodes. Layer-by-layer lamination yielded the ionogel pressure film sensing array, with the entire device having a thickness of only 0.3mm.

[0098] A 5mm × 5mm cell of the thin-film array was measured at a measurement frequency of 1kHz and a measurement voltage of 1V. The sensitivity curve of the cell is shown below. Figure 6 Low-mesh sandpaper has a large particle size, resulting in a more pronounced hierarchical structure in the embossed FEP mold and a larger microstructure on the ionogel surface. PDMS modulus can withstand higher stress and undergo some deformation, leading to greater deformation space for the larger ionogel surface microstructure. Under the combined effect of these two factors, the saturation point of the contact area change shifts towards a higher stress position compared to Example 1, and the sensitivity is also improved. Within a stress range of 0-200 kPa, the sensitivity is 0.145 kPa. -1 The device reaches its most sensitive range between 200-1200 kPa, with a sensitivity of 1.48 kPa. -1 The sensitivity decreased to 0.377 kPa after 1200 kPa. -1 The device has a measurement range of up to 2 MPa, which is excellent for a thin-film sensor under this thickness condition.

[0099] Example 3

[0100] A flexible electrode is selected using a PET substrate coated with a poly(3,4-ethylenedioxythiophene) (PEDOT) film. The entire conductive film measures 20mm × 60mm. After infrared laser etching, an effective conductive area of ​​10mm × 10mm square is created, with a lead wire area of ​​a certain size left. Liquid metal or conductive silver paste can be used to connect the wires to the conductive film. A 0.08mm thick PET single-sided adhesive mask is used, with a 10.2mm × 10.2mm cutout for curing the ionogel, which is then adhered to the conductive side of the flexible electrode. A composite sandpaper structure mold is obtained by sequentially imprinting 400-grit and 240-grit sandpaper onto the 0.08mm thick FEP film. The ionogel for the sensitive layer can be BC / [EMIM][DCA], a thermosetting material where the small-molecule liquid before polymerization can crosslink into a solid state at 50-80℃. The material was dripped onto a composite sandpaper-structured mold, pressed firmly with a flexible electrode covered with a mask, and cured in an 80°C oven before the mask was removed. A 0.2mm thick flexible Eco-flex film was obtained using a scraping process as an insulating layer. This material has a low elastic modulus and was cut into a perforated pattern with a perforation of 10.4mm × 10.4mm. One side was treated with a surface treatment agent for bonding to the PEDOT / PET flexible electrode film. A conductive cloth of the same size as the PEDOT / PET was cut out as the flexible electrode on the other side and bonded to the insulating film using a hot-pressing method. This process of bonding layer by layer resulted in the final device.

[0101] The device is more flexible than the devices in Examples 1 and 2, and the conductive cloth adheres better to the skin surface and other application scenarios compared to PET film.

[0102] The inner dimension of the isolation layer is slightly larger than that of the ion gel. Laser-etched positioning marks are used to locate the isolation layer in the non-conductive areas of the patterned electrode. The thickness of the isolation layer is slightly greater than that of the ion gel and plays a major role in bearing pressure under external loads; both can be considered incompressible solids. The modulus of the isolation layer is higher than that of the ion gel; for example, the modulus of the commercially available PDMS used in Example 2 is 2.3 MPa, while the modulus of the ion gel is only 0.5 MPa. Both PDMS and ion gel are hyperelastic materials, and their modulus increases with increasing compression. Before the electrode contacts the ion gel microstructure, the stress is borne by the isolation layer, while the stress in the suspended portion is borne by the flexible electrode, manifested as the deflection of the electrode film. When the electrode contacts the gel, the stress on the gel is still less than the external load stress, and the height relationship and area ratio of the gel layer and the isolation layer can be designed through finite element simulation. When the lateral deformation of the gel and the isolation layer occupies the reserved gap, the device can hardly continue to compress and deform, and the output capacitance reaches saturation, which can be considered the maximum range of the device. By utilizing the pressure-bearing method of the isolation layer, the pressure range of the device is expanded, but the initial sensitivity is sacrificed. This conclusion can be drawn from the device sensitivity in Example 2.

[0103] In addition to using laser etching to separate conductive and non-conductive areas during electrode patterning, positioning marks, such as crosshairs and outlines, can also be engraved in the non-conductive areas. A mask cut by laser will be used to create marks at the same positions as the electrodes for alignment.

[0104] A hierarchical microstructure is formed by sequentially pressing sandpaper of different mesh sizes. The preferred pressing order is high mesh size first, followed by low mesh size (high mesh size sandpaper has a small particle size, and low mesh size sandpaper has a large particle size). This can be achieved by pressing a 0.08μm FEP film at room temperature and 10MPa pressure for 5 minutes. Figure 7 Electron micrographs of molds imprinted using 1200-grit, 800-grit, and 400-grit sandpaper in different sequences according to embodiments of the present invention are shown: (a) from low to high; (b) from high to low. Figure 7 The layered surface morphology of the FEP mold can be seen, and the imprinting sequence from high to low can retain more small particle indentations.

[0105] Regarding the curing process, a suitable flexible electrode can be selected based on the curing conditions of the gel, including the selection of the electrode substrate and surface coating. For example, the P([BMIM][SPA]-co-MA) ionogel used in Examples 1 and 2 was cured under the following conditions: a wavelength of 365 nm and a curing temperature of 2.8 × 10⁻⁶ ppm. -3 W / cm 2Irradiate under ultraviolet light for 30 minutes. In the examples where PEDOT / PET electrodes are selected, the doped PEDOT material enhances ultraviolet light tolerance, and its conductivity only becomes significantly affected when the ultraviolet dose reaches a certain level. The effect of the ultraviolet dose during the curing process on the electrode is negligible. If a thermal curing method is used to form an ionogel, and a flexible electrode with PET as the substrate is selected, the curing temperature preferably does not exceed 120°C, and the application temperature range of the device is preferably below 60°C.

[0106] Before curing, the electrode surface can be treated with plasma. For example, ITO electrodes, after plasma treatment, exhibit better droplet wettability without affecting their conductivity. The device fabricated in Example 2, for instance, underwent 10,000 cycles of pressure testing, demonstrating good consistency in capacitance response. (See [link to example]). Figure 8 .

[0107] Regarding thickness control methods, a sufficient amount of liquid can be dripped onto the mold first. Then, the flexible electrode with the mask attached is laid flat on the mold surface. A high-transmittance UV optical glass is used to press the electrode and mold together. Weights can be placed around the glass to ensure sufficient pressure, causing excess liquid to be squeezed out. UV light passes through the glass and the flexible electrode, causing the gel to solidify. The gel solidifies at the laser-cut cutouts in the mask, and the gel layer thickness is consistent with the mask thickness. This method is similar in effect to the scraping process. Alternatively, when the mask thickness is large, to ensure the liquid fills the cutouts, a scraping process can be used first to make the liquid level with the mask height before placing the microstructure mold on the surface. If the UV light is directed from the electrode side, the flexible electrode can be laid flat on the high-transmittance UV optical glass before scraping, with the UV lamp irradiating from bottom to top.

[0108] Regarding the design of the elastic modulus of the isolation layer, the range is related to the pressure-bearing capacity of the isolation layer and the deformation space provided by the gap between the isolation layer and the gel layer. That is, the larger the modulus of the isolation layer and the larger the gap, the larger the range, but the device sensitivity will be sacrificed. The design can take all factors into consideration. For example, if PDMS is selected as the isolation layer, the device with a prepolymer:curing agent ratio of 10:1 of PDMS of the same size has a higher range than the device with a prepolymer:curing agent ratio of 5:1, but the sensitivity is lower.

[0109] Regarding the influence of environmental factors: The test environment temperature is controlled by a constant temperature chamber, which can maintain the sensor's environment at the set temperature relatively uniformly. The sensor is placed horizontally inside the constant temperature chamber, and its upper surface is pressed down with a 5g lightweight block to ensure that the gel is in contact with both the upper and lower electrodes during measurement. The electrode leads extend from one side of the constant temperature chamber and connect to a high-speed capacitance measuring instrument to read the capacitance value at the set temperature in real time. Figure 9The following diagram illustrates the temperature drift test of the sensor unit according to an embodiment of the present invention: (a) schematic diagram of the test device; (b) temperature drift test results. Using a capacitor at room temperature (25°C) as the initial reference capacitance, the variation range is only within 0.15 (0.3% / °C), which has minimal impact on the measurement sensitivity of the device. Furthermore, humidity can be controlled by sealing the device to isolate moisture. For example, hydrophobic modified TPU can be used as a flexible electrode substrate, and the device can be sealed by hot pressing.

[0110] In summary, this invention provides a simple and low-cost fabrication process for a wide-range flexible pressure film sensor array using ion gel. This process enables in-situ solidification of ion gel on a flexible conductive film, offering flexibility by allowing for the replacement of structural materials throughout the process based on measurement requirements and application scenarios. The resulting pressure film sensor device exhibits advantages such as high sensitivity, high signal-to-noise ratio, and small size.

[0111] The main advantages of this invention compared to traditional technologies are:

[0112] This invention provides a flexible process for fabricating surface microstructures, offering a solution for balancing sensitivity, linearity, and measurement range in flexible thin-film sensors based on ion gels with limited thickness. Compared to directly using sandpaper of a single mesh size as the surface microstructure, the process of this invention can achieve a sandpaper-level structure, resulting in sensor devices that exhibit good linearity while improving sensitivity in the later stages of a large measurement range. It also provides a low-cost, in-situ patterning process for ion gels, solving the problem of breakage risk associated with traditional processes that involve fabricating thin films first and then transferring them.

[0113] This invention enables the fabrication of thin, low-cost, and flexible patterned ion gel sensor arrays. The devices have a high signal-to-noise ratio, good linearity, small size, flexibility, and portability, and can quickly acquire contact pressure values.

[0114] The solution of this invention exhibits good stability and is easily adjustable across various application scenarios. Specific application scenarios are as follows:

[0115] 1. Wearable Devices: Flexible pressure-sensing films can be applied to wearable devices, such as smart foot pads and smart gloves, for rehabilitation testing and gait detection. By detecting stress changes caused by human movement, relevant information about the human body can be obtained, and combined with other information, it can determine the user's health status. It can also be used in head-mounted devices to detect helmet pressure distribution, improving wearing comfort.

[0116] 2. Smart Home: Flexible sensing films can be embedded in sofas, mattresses, or chairs to monitor users' activity levels and provide functions such as sedentary reminders. Alternatively, they can be combined with other actuators to provide functions such as adjusting seat support and improving posture comfort.

[0117] 3. Intelligent robots: Flexible thin-film pressure sensors can be well covered in parts of robots, such as dexterous hands, that require pressure detection, simulating human touch and improving grasping accuracy.

[0118] 4. Equipment Monitoring: The ultra-thin and bendable flexible pressure sensing film can detect pressure distribution during the assembly of precision parts, preventing overload or assembly defects. It can also be embedded in pouch batteries to detect lithium dendrite growth and monitor expansion pressure during charging and discharging, enabling thermal runaway management. In the printing industry, flexible film sensors can provide data support for optimizing roll tension distribution and reducing material deformation.

[0119] The above description provides a further detailed explanation of the present invention in conjunction with specific / preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various substitutions or modifications can be made to these described embodiments without departing from the concept of the present invention, and all such substitutions or modifications should be considered within the scope of protection of the present invention. In the description of this specification, the reference to terms such as "an embodiment," "some embodiments," "preferred embodiment," "example," "specific example," or "some examples," etc., indicates that the specific features, structures, materials, or characteristics described in connection with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in any suitable manner in one or more embodiments or examples. Without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification and the features of different embodiments or examples. Although the embodiments of the present invention and their advantages have been described in detail, it should be understood that various changes, substitutions, and modifications can be made herein without departing from the scope of protection of the patent application.

Claims

1. An ionogel flexible pressure membrane sensor array, characterized in that, The application relates to a flexible capacitive pressure sensor, comprising: two layers of patterned flexible electrodes; an ionic gel layer composed of an array of ionic gel units with surface microstructures; an isolation layer composed of a non-conductive flexible material with an array of patterned unit structures; wherein the ionic gel layer and the isolation layer are in the same plane, each ionic gel unit is surrounded by a patterned unit structure of the isolation layer, and the two layers of patterned flexible electrodes are respectively arranged on the upper and lower sides of the ionic gel layer and the isolation layer; the ionic gel layer is in contact with the conductive areas of the two layers of flexible electrodes on both sides, the isolation layer is in contact with the non-conductive areas of the two layers of flexible electrodes, and the contact area of the ionic gel layer with the flexible electrodes changes under the action of pressure, thereby causing a change in capacitance. The conductive areas of the two layers of flexible electrodes are arranged in a transverse and longitudinal direction perpendicular to each other to form a sensing array unit; the flexible electrode comprises a substrate and a surface conductive layer, and the conductive layer material comprises silver nanowires (AgNWs), indium tin oxide (ITO) or poly 3,4-ethylenedioxythiophene (PEDOT). The surface microstructure of the ionic gel layer is formed by sandpaper embossing and film turning of a fluorinated ethylene propylene copolymer (FEP) film, and the sandpaper mesh can be selected from at least two combinations of 400 mesh to 1200 mesh. The thickness of the isolation layer is greater than that of the ionic gel layer, the inner ring size of the isolation layer is smaller than the size of the conductive area of the flexible electrode and greater than the size of the ionic gel unit, the material of the isolation layer comprises polydimethylsiloxane (PDMS) or double-sided adhesive tape, and the elastic modulus of the material can be adjusted; the isolation layer and the flexible electrode are bonded by a surface treatment agent or a flexible adhesive. The surface microstructure of the ionic gel layer is a surface microstructure with hierarchical scales.

2. The sensor array of claim 1, wherein, The application further discloses a preparation method of the flexible capacitive pressure sensor, comprising the following steps: S1. performing patterned treatment on the two layers of flexible electrodes by laser etching; S2. preparing a mask with a hollow pattern and covering the mask to the conductive surface of the first flexible electrode; S3. preparing a microstructure mold by embossing a polymer film that can be embossed; S4. adding liquid ionic gel to the mold, pressing the first flexible electrode covered with the mask, and then solidifying to realize in-situ patterned treatment of the ionic gel and microstructure forming, thereby forming an array of ionic gel units with surface microstructures; S5. removing the mold and the mask, and bonding the patterned isolation layer with the first flexible electrode with formed ionic gel and the second flexible electrode, so that each ionic gel unit is surrounded by the patterned isolation layer and is in contact with the conductive areas of the first flexible electrode and the second flexible electrode.

3. The sensor array of claim 1 or 2, wherein, In step S2, the mask is PET single-sided adhesive tape, and the size of the hollow pattern is greater than the size of the conductive area of the flexible electrode; in step S4, the solidification mode is ultraviolet irradiation or heating, and the ionic gel and the first flexible electrode form irreversible adhesion during solidification.

4. The sensor array of any one of claims 1 to 3, wherein, In step S3, a composite sandpaper is used to emboss the microstructure mold on the polymer film, and the composite sandpaper comprises a combination of at least two mesh sandpapers; by sequentially embossing sandpapers with different mesh, a surface microstructure with hierarchical scales is formed on the microstructure mold.

5. The sensor array of any one of claims 1 to 4, wherein, In step S4, the thickness of the ionic gel is controlled by the thickness of the mask, and the thickness of the mask is 0.08 mm to 0.5 mm.

6. A method of fabricating an ionogel flexible pressure membrane sensor array, comprising: ​ ​ ​ ​ ​ ​ 7. The preparation method according to claim 6, characterized in that, ​ 8. The production method according to claim 6 or 7, characterized by, ​ 9. The production process according to any one of claims 6 to 8, characterized in that, ​ 10. The method of claim 9, wherein the step of preparing is characterized by, The isolation layer in step S5 is formed by blade coating, spin coating or cutting a pre-made film, and its surface is treated with a modifier to improve adhesion; the thickness of the isolation layer is 0.2 mm to 1 mm, and the inner ring size is 0.2 mm to 0.4 mm larger than the ion gel unit.

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