A multi-modal flexible bio-inspired electronic skin

Abstract

The application relates to the field of bionic electronic technology and provides a multi-modal flexible bionic electronic skin which comprises, from top to bottom, a temperature sensing unit, a friction force sensing unit and a pressure sensing unit; the temperature sensing unit comprises a first flexible substrate layer and two first electrodes which are mutually nested and connected at inner ends; the first electrode is composed of temperature-sensitive material; the friction force sensing unit comprises a second flexible substrate layer, two second electrodes which are mutually nested and a flexible elastic dielectric material arranged between the two second electrodes and serving as a capacitor; the pressure sensing unit comprises two third electrodes which are connected with lower ends of the second flexible substrate layer and mutually nested, and a pressure-sensitive layer located at lower ends of the two third electrodes; the application realizes in-situ synchronous sensing and physical decoupling of three physical quantities of pressure, friction force and temperature, avoids crosstalk among multi-physical signals, and simultaneously maintains the ultra-thin and flexible nature of the device.

Description

Technical Field

[0001] This invention belongs to the field of bionic electronics technology and provides a multimodal flexible bionic electronic skin. Background Technology

[0002] As the largest organ in the human body, the skin covers the entire body and can sense the external environment in multiple modes (such as temperature, pressure, friction, etc.) and protect the human body from harm. With the advancement of science and technology, various flexible electronic devices, robots and intelligent prostheses are developing rapidly. Bionic electronic skin has also emerged, making the functions of prostheses or robots closer to the functions of the human body itself, which can help people with physical defects to achieve a better quality of life.

[0003] Currently, existing bionic electronic skin multimodal sensing integration typically employs composite materials or microstructure designs in a single sensitive layer. By optimizing materials or structures, different physical signals can be distinguished. However, the sensitive material in a single sensitive layer needs to respond to multiple physical fields simultaneously (such as temperature changes causing changes in material resistance, while pressure deformation also changes its resistance). Furthermore, the mechanisms by which each physical field affects the material are superimposed and cannot be separated, leading to distorted and inaccurate output signal data. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a multimodal flexible bionic electronic skin capable of in-situ synchronous sensing and physical decoupling of three physical quantities: pressure, friction, and temperature.

[0005] The technical solution of the present invention includes the following components that are sequentially attached from top to bottom: The temperature sensing unit includes a first flexible substrate layer and two equidistant concentric spiral first electrodes. Both first electrodes are connected to the upper end of the first flexible substrate layer and are nested together. The internal endpoints of the two first electrodes are connected to each other. The first electrodes are made of a conductive temperature-sensitive material.

[0006] The friction sensing unit includes a second flexible substrate layer, two equidistant concentric spiral second electrodes, and a flexible elastic dielectric material. The two second electrodes are connected to the upper end of the second flexible substrate layer and are nested together. A flexible elastic dielectric material is provided between the two second electrodes to act as a capacitor, and the flexible elastic dielectric material connects the first flexible substrate layer and the second flexible substrate layer.

[0007] The pressure sensing unit includes two equidistant concentric spiral third electrodes and a pressure-sensitive layer. Both third electrodes are connected to the lower end of the second flexible substrate layer, and the two third electrodes are nested together. The pressure-sensitive layer is located at the lower end of the two third electrodes.

[0008] When the temperature changes, the resistance of the first electrode changes, and the temperature change is detected based on the resistance of the first electrode. When friction occurs, the distance between the two second electrodes changes, which in turn changes the area of ​​the effectively overlapping flexible elastic dielectric material. The friction force is detected based on the change in capacitance. When the pressure changes, the third electrode squeezes the pressure-sensitive layer, which changes the conductive network inside the pressure-sensitive layer, thereby causing a change in resistance. The pressure magnitude is detected based on the change in resistance.

[0009] Furthermore, the first flexible substrate layer, the second flexible substrate layer, and the third flexible substrate layer are all made of polyimide material.

[0010] Furthermore, the thickness of the first electrode is between 180 nm and 220 nm, the thickness of the second electrode is between 15 μm and 25 μm, and the thickness of the third electrode is between 140 nm and 160 nm.

[0011] Furthermore, the material of the first electrode is platinum.

[0012] Furthermore, the fabrication method of the temperature sensing unit includes: A platinum thin film is formed on a first flexible substrate by magnetron sputtering, and then a negative photoresist is spin-coated onto the platinum thin film to obtain a base element with a photoresist layer.

[0013] The photoresist layer is flattened and pre-baked. The photoresist layer is then exposed according to the photomask to obtain a preliminary element with two equidistant concentric spiral photoresists. The preliminary element is then immersed in the developer and cleaning solution in sequence.

[0014] After the preliminary element is soaked, it is post-baked and then the platinum film in the preliminary element is etched to obtain a preliminary unit with two equidistant concentric spiral first electrodes, and the inner ring ends of the two first electrodes are connected to each other.

[0015] The photoresist in the initial unit is removed by using an alkaline stripper to obtain the final temperature sensing unit.

[0016] Furthermore, the fabrication method of the friction sensing unit includes: A conductive layer is deposited on the upper surface of the second flexible substrate by magnetron sputtering, and then the conductive layer is etched to form a preliminary unit of two equidistant concentric spiral second electrodes, with the inner ring ends of the two second electrodes not connected to each other.

[0017] A PDMS dielectric is coated onto the initial unit, and the PDMS dielectric covers the second electrode, thereby forming a pressure sensing unit.

[0018] Furthermore, the fabrication method of the pressure sensing unit includes: A conductive layer is deposited on the lower end face of the second flexible substrate by magnetron sputtering, and then a negative photoresist is spin-coated on the conductive layer to obtain a base element with a photoresist layer.

[0019] The photoresist layer is flattened and pre-baked, and then exposed according to the photomask to obtain a preliminary element with two equidistant concentric spiral photoresists. The preliminary element is then immersed in the developer and cleaning solution in sequence.

[0020] After the preliminary element is soaked, it is post-baked, then the conductive film in the preliminary element is etched, and then the photoresist is removed to obtain a preliminary unit with two equidistant concentric spiral electrodes.

[0021] Photocurable flexible resin and multi-walled carbon nanotubes are mixed in a preset ratio, magnetically stirred, and then printed to obtain a sensing layer. The sensing layer is then soaked in isopropanol and cured to obtain a flexible piezoresistive sensing layer. The flexible piezoresistive sensing layer and electrodes are bonded and encapsulated to obtain a pressure sensing unit.

[0022] Furthermore, the method for spin-coating negative photoresist is as follows: negative photoresist is spin-coated on a platinum thin film at a rotation speed of 3000 rpm to form a photoresist layer with a thickness of 1.8 μm to 2.2 μm.

[0023] Furthermore, the pre-baking process involves first drying the photoresist layer at 65°C for 5 minutes, and then drying it at 95°C for 15 minutes.

[0024] Post-drying treatment: drying at 150℃ for 10 minutes, with an exposure dose of 50. .

[0025] The technical solution provided by this invention has the following advantages compared with the prior art: This invention employs a vertically heterogeneous integrated architecture where temperature, friction, and pressure sensing units are sequentially bonded from top to bottom. On one hand, it constructs three completely heterogeneous and independent physical sensing channels, achieving specific detection of temperature, friction, and pressure based on resistive heating, capacitance area change, and piezoresistive effects, respectively. This completely severs the coupling paths of multiple physical signals both spatially and mechanistically, achieving in-situ synchronous sensing of the three physical quantities and decoupling from the source physical components, thus completely eliminating signal crosstalk. On the other hand, the integrated approach eliminates physical gaps and redundant interfaces caused by post-assembly. Furthermore, the shared second flexible substrate layer between the friction and pressure sensing units further reduces interface mismatch, significantly reducing the overall device thickness, improving flexibility and conformal bonding capabilities, ensuring synchronized response times for each unit, and eliminating shear stress concentration sources at the interface under dynamic bending and tensile loads. This effectively avoids device delamination, cracking, and electrical contact failure, significantly improving the long-term reliability of the electronic skin under complex dynamic conditions.

[0026] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a three-dimensional structural diagram of the bionic electronic skin according to an embodiment of the present invention.

[0029] Figure 2 This is a schematic diagram of the planar structure of the bionic electronic skin according to an embodiment of the present invention.

[0030] Figure 3 for Figure 2 Cross-sectional view of section AA.

[0031] Figure 4 for Figure 3 Enlarged view at point B Figure label: 1. First flexible substrate layer; 2. First electrode; 3. Second flexible substrate layer; 4. Second electrode; 5. PDMS dielectric; 6. Third electrode; 7. Pressure-sensitive layer. Detailed Implementation

[0032] The following detailed description of a specific embodiment of the present invention is provided in conjunction with the accompanying drawings. However, it should be understood that the scope of protection of the present invention is not limited to the specific embodiment.

[0033] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the technical solution of this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0034] In the description of the embodiments of the present invention, unless otherwise stated, "a plurality of" means two or more.

[0035] In the description of the embodiments of the present invention, the flexible elastic dielectric material is one of polydimethylsiloxane PDMS, polyurethane elastomer, methyl vinyl silicone rubber, fluororubber, etc., and this application uses polydimethylsiloxane PDMS as an example.

[0036] Example 1: like Figures 1 to 4 As shown, this embodiment provides a multimodal flexible bionic electronic skin. The electronic skin includes, from top to bottom, a temperature sensing unit, a friction sensing unit, and a pressure sensing unit that are sequentially attached to each other.

[0037] The temperature sensing unit includes a first flexible substrate layer 1 and two equidistant concentric spiral first electrodes 2. Both first electrodes 2 are connected to the upper end of the first flexible substrate layer 1, and the two first electrodes 2 are nested together. The internal endpoints of the two first electrodes 2 are connected to each other. The first electrodes 2 are made of a conductive temperature-sensitive material.

[0038] Specifically, in this embodiment, the so-called "equidistant concentric spiral nesting" refers to two spiral electrodes intertwined like a double helix structure, but maintaining equal spacing in space and not contacting each other, with electrical conduction only at the internal endpoints. This design, where the internal endpoints are interconnected, makes the two nested spiral electrodes essentially form a continuous temperature-sensing resistance loop. When the external ambient temperature changes, the resistivity of the first electrode 2, as a temperature-sensitive material, changes linearly with temperature, thereby detecting temperature changes based on the resistance change of the first electrode 2. More importantly, the equidistant concentric spiral structure possesses excellent strain decoupling characteristics: when the electronic skin bends or stretches with the robot's joints, the spiral structure converts the externally applied axial strain into minute rotations and gap expansions of the spiral segments, rather than direct axial stretching of the non-metallic conductor. This greatly suppresses resistance fluctuations caused by mechanical deformation, ensuring that the temperature measurement signal is not interfered with by skin deformation. It should be understood that although this embodiment demonstrates the form of two nested electrodes, in other embodiments, as long as the internal endpoints are connected to form a loop and the spiral structure can resolve axial strain, the specific number of coils or linewidth of the electrodes can be adjusted according to sensitivity requirements.

[0039] The friction sensing unit includes a second flexible substrate 3, two equidistant concentric spiral second electrodes 4, and a PDMS medium 5. The two second electrodes 4 are connected to the upper end of the second flexible substrate 3 and are nested together. The PDMS medium 5 is provided between the two second electrodes 4 to act as a capacitor, and the PDMS medium 5 connects the first flexible substrate 1 and the second flexible substrate 3.

[0040] Specifically, unlike the temperature sensing unit, the inner ends of the two second electrodes 4 in the friction sensing unit are not connected; they are physically separated by the PDMS dielectric 5, thus forming the two poles of a capacitor. When friction, i.e., lateral shear force, occurs, the distance between the two second electrodes 4 changes, thereby changing the area of ​​the effectively overlapping PDMS dielectric 5. The friction force is detected based on the change in capacitance. This detection mechanism based on area change is the core of achieving decoupling between friction force and pressure: the application of normal pressure mainly leads to the compression of the electrode spacing, but due to the structural rigidity of the second electrodes 4 and the limited elastic deformation of the PDMS dielectric 5, the effect of spacing compression on capacitance is effectively suppressed; while the lateral shear force directly causes the two nested spiral electrodes to slide relative to each other in the horizontal direction. This sliding instantaneously changes the effective overlapping area of ​​the electrodes, causing a significant output of capacitance value. Therefore, this unit can purely respond to lateral friction and is almost unaffected by fluctuations in normal gripping force. In other embodiments, the material serving as the capacitor dielectric is not limited to PDMS; any polymer with good elasticity and dielectric properties can be used, as long as it allows the plates to slip relative to each other under shear force to change the overlap area.

[0041] The pressure sensing unit includes two equidistant concentric spiral third electrodes 6 and a pressure-sensitive layer 7. Both third electrodes 6 are connected to the lower end of the second flexible substrate 3, and the two third electrodes 6 are nested together. The pressure-sensitive layer 7 is located at the lower end of the two third electrodes 6.

[0042] Specifically, the pressure sensing unit is located at the bottom layer of the entire electronic skin, directly bearing the normal pressure of the contacting object. When the pressure changes, the third electrode 6 compresses the pressure-sensitive layer 7, causing a change in the conductive network inside the pressure-sensitive layer 7, thereby causing a change in resistance. The pressure magnitude is detected based on the change in resistance. The interior of the pressure-sensitive layer 7 is filled with a percolation network formed by conductive fillers. When not under pressure, the conductive fillers maintain their initial contact state; when normal pressure is applied, the pressure-sensitive layer 7 undergoes elastic compression, increasing the number of contact points and reducing the spacing of the internal conductive fillers, enhancing the quantum tunneling effect or increasing the direct conductive pathway, resulting in a decrease in the overall resistance value. Once the pressure is removed, the pressure-sensitive layer 7 recovers its deformation through its own elasticity, and the conductive network returns to its initial state, achieving repeatable pressure sensing. It should be understood that although the figure shows a stacked structure with the pressure-sensitive layer 7 located below the third electrode 6, in other alternative embodiments, the pressure-sensitive layer 7 can also adopt a three-dimensional encapsulation form that surrounds the third electrode 6, as long as the mechanism that allows the normal pressure to be effectively transmitted to the conductive network and cause a change in resistance is met.

[0043] This embodiment establishes a working mode with independent mechanisms and independent signal output through the aforementioned vertical heterogeneous integration architecture. The temperature sensing unit measures temperature based on the resistive heating effect, the friction sensing unit measures shear force based on changes in capacitance area, and the pressure sensing unit measures normal force based on changes in piezoresistive networks. These three units are completely heterogeneous in their physical sensing mechanisms, synchronously superimposed in situ, and their respective electrical signals are output to an external controller via independent leads, without interference. This design fundamentally eliminates the persistent crosstalk problem caused by multi-physics coupling, achieving in-situ synchronous sensing and physical decoupling of the three physical quantities: pressure, friction, and temperature. This provides a solid structural foundation for subsequent advanced process and material implementations.

[0044] Example 2: Based on Example 1, this example further refines the design of the substrate material, electrode thickness, and temperature-sensitive material of the multimodal flexible bionic electronic skin.

[0045] The first flexible substrate layer 1, the second flexible substrate layer 3, and the third flexible substrate layer are all made of polyimide. Specifically, polyimide (PI) was chosen as the flexible substrate because of its excellent high-temperature stability and excellent flexibility. In practical applications of electronic skin, devices often need to be attached to surfaces with varying curvatures, such as robot joints or human skin. The high elongation at break and low elastic modulus of PI material allow it to bend and stretch along with the substrate without brittle fracture. At the same time, when sensing high-temperature objects, the extremely high glass transition temperature and thermal decomposition temperature of PI ensure that the substrate will not soften or thermally degrade in high-temperature environments, thereby maintaining the stability of the upper sensing unit structure and the reliability of signal output. It should be understood that although PI material is preferred in this embodiment, in other scenarios with slightly lower temperature resistance requirements, flexible polymers such as polyethylene terephthalate (PET) or polydimethylsiloxane (PDMS) can also be used as substrates, as long as they can meet the flexibility and support requirements under specific working conditions.

[0046] Regarding the electrode thickness design, the thickness of the first electrode 2 is between 180nm and 220nm, the thickness of the second electrode 4 is between 15µm and 25µm, and the thickness of the third electrode 6 is between 140nm and 160nm. This thickness range is not arbitrarily chosen, but rather a critical window derived from in-depth consideration of the physical mechanisms of each sensing unit and extensive experimental verification. Specifically, for the first electrode 2, a preferred thickness example is 200nm. This thickness ensures that the platinum thin film has sufficient sheet resistance to output easily acquired weak resistance change signals, while avoiding excessive film thickness leading to increased mechanical stiffness and weakening the strain release effect of the spiral structure. If an external comparison ratio is set, reducing the thickness of the first electrode 2 to 100nm, the film resistance will be too low, making it highly susceptible to external electromagnetic interference or contact resistance fluctuations, resulting in a severe deterioration of the temperature measurement signal-to-noise ratio. Conversely, if the thickness is too large, the spiral structure will struggle to conformally deform with the flexible substrate, significantly diminishing the strain interference suppression function. For the second electrode 4, a preferred thickness example is 20 μm. This micrometer-level thickness provides sufficient structural rigidity, making it less prone to bending or collapse under normal pressure. This ensures the stability of the capacitor plate spacing, allowing the capacitor output to respond only to changes in the effective overlap area caused by lateral shear force. If an off-limits comparison is set, reducing the thickness of the second electrode 4 to 5 μm, the electrode rigidity becomes severely insufficient. Under normal gripping force, uncontrollable spacing compression occurs between the plates, leading to severe crosstalk between the frictional force signal and the pressure signal, completely destroying the decoupling sensing function. For the third electrode 6, a preferred thickness example is 150 nm. This nanometer-level thickness, while ensuring conductive extraction, minimizes the mechanical resistance of the electrode itself to the elastic compression of the pressure-sensitive layer 7, ensuring that normal pressure can be transmitted to the conductive network of the pressure-sensitive layer 7 without loss. It should be understood that the above numerical range covers the endpoint and intermediate values. In actual fabrication, it can be finely adjusted within the range according to specific sensitivity and rigidity requirements. However, deviating from this critical window will make it difficult to balance signal quality and decoupling performance.

[0047] Regarding the temperature-sensitive material of the temperature sensing unit, the first electrode 2 is made of platinum. Specifically, platinum is chosen as the temperature-sensitive electrode because of its extremely high temperature coefficient of resistance (TCR) and excellent chemical inertness. A high TCR means that a small change in temperature can cause a significant linear change in the platinum resistance, thus giving the temperature sensing unit extremely high temperature sensitivity. Chemical inertness ensures that the platinum electrode does not oxidize or corrode in complex environments or even slightly acidic or alkaline atmospheres, guaranteeing the long-term stability of the device. More importantly, combined with the equidistant concentric spiral nested structure in Example 1, platinum exhibits optimal temperature measurement error suppression under small strain. This is because the platinum thin film mainly undergoes in-plane rotation and gap expansion / contraction in the spiral structure, rather than axial stretching. Its intrinsic strain resistivity change is effectively diluted by the spiral geometry, making the resistance drift caused by strain much smaller than the resistance change caused by temperature, achieving high-fidelity temperature measurement. To prevent circumvention, this invention includes an equivalent alternative: in other embodiments, the first electrode 2 can also be made of gold or a nickel-chromium alloy as the temperature-sensitive material. Gold also possesses good chemical stability and ductility, while nickel-chromium alloys offer a wider temperature measurement range and cost advantages. However, gold's temperature coefficient of resistance under small strain is slightly inferior to platinum, and the resistance drift caused by strain is relatively large; although nickel-chromium alloys have acceptable TCR, their temperature measurement error suppression effect under extremely small strain is not as excellent as that of platinum thin films. Therefore, platinum exhibits irreplaceable comprehensive advantages in meeting the combined requirements of small strain and high-precision temperature measurement, making it the preferred embodiment of this invention.

[0048] This embodiment further solidifies the physical quantity decoupling mechanism established in Embodiment 1 from the perspectives of material properties and microscale by synergistically limiting the substrate material, thickness range, and temperature-sensitive material, ensuring the high signal-to-noise ratio and low crosstalk characteristics of multimodal sensing under actual complex working conditions.

[0049] Example 3: Based on Examples 1 and 2, this example further details the fabrication method of the temperature sensing unit, focusing on how photolithography etching process precisely serves the forming and functional realization of the equidistant concentric spiral nested structure.

[0050] In step S100, a platinum thin film is deposited on the first flexible substrate 1 by magnetron sputtering, and then a negative photoresist is spin-coated onto the platinum thin film to obtain a base element with a photoresist layer. Specifically, the magnetron sputtering process ensures that the platinum thin film has excellent adhesion and uniform thickness distribution on the polyimide substrate, which is the basis for subsequent patterning of high-precision spiral structures. After spin-coating the negative photoresist, the photoresist layer will serve as a masking and protective layer against etchant erosion. It should be understood that although this embodiment preferably uses negative photoresist to obtain a steeper sidewall protection morphology, in other embodiments compatible with exposure equipment and processes, positive photoresist can also be used in conjunction with a corresponding mask design, as long as the required spiral nesting pattern can be accurately defined in the end.

[0051] Step S200 involves planarizing and pre-baking the photoresist layer, then exposing it according to the photomask to obtain a preliminary element with two equidistant concentric spiral photoresist elements. The preliminary element is then sequentially immersed in developer and cleaning solutions. The core of this step lies in how the specific design of the photomask coordinates with the exposure process to ensure that the patterned structure accurately achieves the structural features of "two equidistant concentric spirals" with "interconnected inner ends." Specifically, the light-transmitting pattern on the photomask is not two independent spirals, but is specifically designed to retain a tiny light-transmitting bridging region at the inner endpoints of the two spirals. Since a negative photoresist is used, the exposed area is retained after development. Therefore, this bridging light-transmitting region forms a photoresist bridge connecting the inner ends of the two spirals after development, thus physically and logically ensuring the interconnection of the internal endpoints of the two first electrodes 2. This design is a key process guarantee for realizing a single continuous resistance loop in the temperature sensing unit. If the photomask does not have this bridging, the two spirals will be completely broken after etching, making it impossible to form an effective temperature measurement path. The process of soaking in the developer and cleaning solution requires strict control of time and temperature to thoroughly remove the photoresist from the unexposed areas, while avoiding over-development that could lead to a reduction in the bridging area or spiral linewidth.

[0052] In step S300, after the preliminary element is immersed, it undergoes a post-baking process, followed by etching of the platinum thin film within the preliminary element to obtain a preliminary unit with two equidistant concentric spiral first electrodes, with the inner ends of the two first electrodes interconnected. The post-baking process aims to further cross-link and solidify the retained photoresist pattern, enhancing its etching resistance. The subsequent platinum thin film etching step is crucial in determining the final quality of the spiral nested structure. Specifically, the etching step preferably uses a potassium iodide-iodine etchant for wet etching. This etchant has extremely high etching selectivity for platinum, and its etching mechanism is isotropic. To accurately achieve this nested connection pattern without causing the inner ends to break, the etching time and temperature must be strictly controlled. Because the linewidth at the inner ring connection is extremely narrow, if the etching time is too long, isotropic etching will cause severe lateral drilling of the platinum film beneath the photoresist, easily severing the platinum wires, which are only a few micrometers wide, at the inner ring connection bridge, thus destroying the structure connecting the internal endpoints. If the etching time is insufficient, platinum metal burrs will remain between the spiral lines, leading to a short circuit risk. Therefore, by accurately calculating the platinum film thickness and etching rate, the etching time must be controlled within a window that just penetrates the film without lateral drilling eroding the critical width of the connection bridge to ensure the integrity of the inner ring connection. It should be understood that in other high-precision implementations, equivalent dry etching processes such as reactive ion etching can also be used, whose anisotropic etching characteristics can better suppress lateral drilling, further improving the forming accuracy and reliability of the inner ring connection.

[0053] In step S400, the photoresist in the preliminary unit is removed using an alkaline stripping solution to obtain the final temperature sensing unit. The stripping step is not only for removing the masking layer but also for ensuring the smoothness of the spiral structure's edges. Specifically, immersion in an alkaline stripping solution at a suitable temperature gently and thoroughly dissolves the cross-linked negative photoresist, including the tiny photoresist bridge at the inner ring connection. If the stripping process is too harsh or incomplete, photoresist residue can easily adhere to the edges of the spiral or the nested gaps, forming insulating burrs. This would alter the effective resistance baseline of the first electrode 2 and disrupt the gap expansion and contraction mechanism during strain release. Gentle and thorough stripping ensures that the platinum spiral structure exposes a smooth and flat edge morphology, allowing the electrode to smoothly undergo in-plane rotation and gap changes under tension, thus perfectly achieving the temperature detection function resistant to strain interference. Thus, through the dual binding of the above process steps and structural function, the fabrication of the temperature sensing unit is completed with high quality.

[0054] Example 4: Based on Examples 1 and 2, this example further details the fabrication method of the friction sensing unit, focusing on how magnetron sputtering and etching processes serve the molding of capacitor plates with "unconnected inner rings" and the interface reliability mechanism of the embedded packaging structure formed by PDMS coating.

[0055] In step S500, a conductive layer is deposited on the upper surface of the second flexible substrate 3 by magnetron sputtering, and then the conductive layer is etched to form a preliminary unit of two equidistant concentric spiral second electrodes 4, with the inner ends of the two second electrodes 4 not connected to each other. Specifically, unlike the design in the temperature sensing unit where the inner ends of the first electrode 2 are connected to form a single resistive circuit, the friction sensing unit requires that the two second electrodes 4 be electrically isolated. This design of the inner ends not being connected is a necessary condition for forming the two electrodes of the capacitor. Only when the two spiral electrodes are completely independent can they act as the upper and lower electrodes of the capacitor, respectively, thereby outputting a capacitance signal by changing the effective overlap area through relative sliding when a lateral shear force is applied. If the inner ends are misconnected, the capacitor structure will be short-circuited, and the friction sensing function will be completely disabled. Therefore, precise control of the electrode spacing must be ensured in the etching process. Because the two equidistant concentric spiral electrodes are nested and coiled, the gap between them is extremely small. Lateral drilling or over-etching during the etching process can easily cause bridging and short circuits at the originally isolated inner ring ends, or increase the nesting gap, thereby reducing the capacitance base value and sensitivity. Only by precisely controlling the etching time and etchant concentration, and keeping the lateral etching amount within the safe margin of the electrode spacing, can the accuracy and stability of the insulation gap between the two electrodes be ensured. It should be understood that although this embodiment preferably uses wet etching to achieve high-efficiency batch processing, in other embodiments with extremely high requirements for electrode spacing accuracy, dry reactive ion etching can also be used, utilizing its anisotropic etching characteristics to obtain steeper electrode sidewalls, further eliminating the risk of bridging at the inner ring ends.

[0056] Furthermore, the thickness of the second electrode 2 is set according to actual needs. When the thickness generated by magnetron sputtering cannot meet the required thickness, it can be increased by other means, such as electroplating.

[0057] In step S600, PDMS dielectric 5 is coated onto the preliminary unit, so that PDMS dielectric 5 covers the second electrode 4, thereby forming a friction sensing unit. The core of this step lies not only in filling the dielectric material to form a capacitor, but also in solving the persistent problem of interface reliability between metal and polymer through the embedded encapsulation of PDMS. Specifically, the second electrode 4 is usually made of a metal with high rigidity, such as copper, while the second flexible substrate layer 3 and PDMS dielectric 5 are both low-modulus elastic polymers. When the electronic skin is subjected to repeated lateral shear forces under dynamic conditions, a serious mechanical impedance mismatch will occur between the rigid metal electrode and the elastic polymer. If the electrode is simply laid flat on the dielectric surface, the shear force will cause huge stress concentration at the interface, which can easily lead to delamination, warping, or even cracking of the rigid electrode. The PDMS encapsulation process used in this embodiment allows liquid PDMS to flow naturally into and fill the gaps and sidewalls of the spiral electrode during the coating and curing process, forming a three-dimensional encapsulation structure in which the second electrode 4 is partially or completely embedded. This embedded packaging utilizes the elastic constraint of PDMS to uniformly disperse interfacial stress into the surrounding elastomer under shear force, rather than concentrating it on the two-dimensional metal-polymer contact surface, thus effectively suppressing interfacial delamination. Simultaneously, the PDMS wrapping around the electrode edges acts like an elastic buffer layer on a rigid skeleton, preventing irreversible collapse of the plates under normal pressure, ensuring the stability of the capacitor spacing and the purity of the frictional force signal. It should be understood that in other embodiments, the material acting as the coating medium is not limited to PDMS; any polymer with good dielectric properties that can form an embedded elastic constraint through coating and curing, such as polyurethane elastomers or silicone rubber, can be used as an alternative, as long as it can effectively disperse interfacial stress and prevent delamination of the rigid electrodes.

[0058] This embodiment, through the above-described fabrication process, not only precisely realizes the capacitor plate structure of "inner rings not connected to each other" in the friction sensing unit, but also fundamentally solves the interface failure problem caused by the metal-polymer mechanical impedance mismatch through PDMS embedded packaging, providing a solid process guarantee for the long-term stable operation of electronic skin under complex dynamic loads.

[0059] Example 5: Based on Examples 1 and 2, this example further details the preparation method of the pressure sensing unit, focusing on the formation mechanism of the micro-network of the 3D printed percolation effect pressure-resistant layer, and the key role of isopropanol immersion curing in improving the stability of the pressure-sensitive layer.

[0060] In step S700, a conductive layer is deposited on the lower end face of the second flexible substrate layer 3 by magnetron sputtering, and then a negative photoresist is spin-coated onto the conductive layer to obtain a base element with a photoresist layer. Specifically, the electrode fabrication of the pressure sensing unit is similar to that of the temperature sensing unit, both requiring the deposition of a conductive thin film on the flexible substrate and patterning via photolithography. The lower end face of the second flexible substrate layer 3 is the back face opposite to the friction sensing unit. This spatial arrangement of the upper and lower end faces fully utilizes the thickness dimension of the flexible substrate, achieving vertical heterogeneous integration of the sensing unit and avoiding area expansion and signal cross-interference caused by planar layout.

[0061] In step S800, the photoresist layer is planarized and pre-baked. Then, the photoresist layer is exposed according to the mask to obtain a preliminary element with two equidistant concentric spiral photoresist elements. The preliminary element is then sequentially immersed in the developer and cleaning solution. The process logic of this step is consistent with the photolithography process of the temperature sensing unit, aiming to accurately define the nested spiral mask pattern. It should be understood that although similar photolithography parameters and processes as the temperature sensing unit are used here, since the pressure sensing unit operates based on the piezoresistive effect rather than the resistive heating effect, the function of the third electrode 6 is to act as a conductive lead-out terminal in contact with the pressure-sensitive layer 7. Therefore, its material selection can be more extensive, not limited to platinum. Equivalent high-conductivity metals such as copper, gold, or silver can also be used, as long as a low-resistance contact with the pressure-sensitive layer 7 can be ensured.

[0062] In step S900, after the preliminary element is soaked, it undergoes a post-baking process, followed by etching of the conductive film. Then, it is immersed in an alkaline resist remover solution (NMP, N-methylpyrrolidone) for 30 minutes to remove the photoresist, resulting in a preliminary unit with two equidistant concentric spiral electrodes. After etching and resist removal, the spiral nested structure of the third electrode 6 is finally formed. The design consideration of this structure is that the equidistant concentric spirals can uniformly collect the resistance change signal generated by the pressure-sensitive layer 7 under pressure within their coverage area, avoiding the gradient attenuation problem of traditional interdigitated electrodes where the signal is strong at the edge and weak in the center, thus significantly improving the spatial uniformity and sensitivity of pressure sensing.

[0063] In step S1000, photocurable flexible resin and multi-walled carbon nanotubes are mixed in a preset ratio, magnetically stirred, and then printed to obtain a sensing layer. The sensing layer is then immersed in isopropanol and cured to obtain a flexible piezoresistive sensing layer 7. The flexible piezoresistive sensing layer 7 and the third electrode 6 are then bonded and encapsulated to obtain a pressure sensing unit. This step is the core of the pressure sensing unit fabrication, and its key lies in the construction of the percolation effect micro-network and the post-processing curing mechanism.

[0064] Specifically, the so-called "percolation effect" refers to the physical phenomenon where, when the concentration of randomly dispersed conductive fillers in an insulating elastomeric substrate reaches a critical value, namely the percolation threshold, a through-conductive network forms between the fillers, causing the composite material to abruptly change from an insulating state to a conductive state. In this embodiment, photocurable flexible resin is used as the insulating substrate, and multi-walled carbon nanotubes (MWCNTs) are used as the conductive fillers. During magnetic stirring, MWCNTs are uniformly dispersed in the resin. When their concentration reaches the percolation threshold, the tubes physically overlap and are attracted by van der Waals forces due to their extremely high aspect ratio, forming a three-dimensional microscopic conductive network. At this time, under no pressure, the MWCNT network maintains its initial contact state and spacing, exhibiting a certain initial resistance. When normal pressure is applied, the flexible resin undergoes elastic compression, increasing the number of contact points and reducing the spacing between MWCNTs. This significantly enhances the quantum tunneling effect or greatly increases the direct conductive pathways, resulting in a sharp decrease in the macroscopic resistance value. Once the pressure is removed, the flexible resin recovers its deformation through its own elasticity, and the MWCNT network returns to its initial contact state, restoring the resistance value. This mechanism, based on changes in contact state rather than irreversible deformation, is the microscopic foundation for achieving high repeatability and long-term stability of pressure signals. It should be understood that while MWCNTs are preferred as the conductive filler in this embodiment, in other embodiments, equivalent nanoconductive materials such as carbon black, graphene, or silver nanowires can also be used, as long as they can reach the percolation threshold and form a reversible contact network in the elastic substrate.

[0065] More importantly, the printed sensing layer needs to be removed and cured by immersion in isopropanol. This post-processing step is not a simple cleaning, but an interface remodeling process that plays a decisive role in the stability of the pressure-sensitive layer 7. During 3D printing, the rapid cross-linking of the photocurable resin often encapsulates unreacted monomers and microbubbles introduced during stirring. These defects cause the pressure-sensitive layer 7 to undergo localized irreversible plastic deformation rather than pure elastic compression under stress, thereby destroying the contact reversibility of the MWCNTs network and causing severe baseline drift and signal hysteresis. Isopropanol, as a good solvent, can penetrate into the interior of the sensing layer, dissolving and removing unreacted monomers and microbubbles. At the same time, its solvent effect promotes further extension and deep cross-linking of the resin macromolecular chains. After being removed from the isopropanol and finally cured, the pressure-sensitive layer 7 obtains a denser and more cross-linked elastomer structure, with its internal MWCNTs network stably anchored in the highly cross-linked resin backbone. This structure ensures that under normal pressure, the flexible piezoresistive sensing layer 7 undergoes only an elastic reversible change in the contact state of MWCNTs, while the resin matrix itself does not undergo irreversible plastic flow or damage, fundamentally eliminating the hysteresis and creep problems of piezoresistive sensors.

[0066] Finally, the flexible piezoresistive sensing layer 7, obtained by isopropanol immersion curing, is bonded and encapsulated with the third electrode 6 to complete the fabrication of the pressure sensing unit. The bonding and encapsulation process must ensure that the spiral nested areas of the piezoresistive layer 7 and the third electrode 6 are completely aligned and in close contact to achieve efficient extraction of resistance change signals. This embodiment, through the above process, not only constructs a highly sensitive piezoresistive network based on the percolation effect, but also, through the key step of isopropanol immersion curing, endows the piezoresistive layer 7 with excellent elastic recovery and fatigue resistance, providing a solid material and process guarantee for the long-term accurate pressure sensing of electronic skin under dynamic loads.

[0067] Example 6: Based on Examples 3 and 5, this example further refines the key parameters in the photolithography process, focusing on the critical window settings of spin coating, pre-baking, post-baking, and exposure parameters and their decisive influence on the forming quality of equidistant concentric spiral nested structures.

[0068] Regarding spin-coating parameters for photoresist, the method for spin-coating negative photoresist is as follows: negative photoresist is spin-coated onto a platinum or conductive film at 3000 rpm to form a photoresist layer with a thickness of 2 μm. Specifically, the thickness of the photoresist layer directly determines the erosion resistance of the masking layer and the resolution of the pattern during development. A thickness of 2 μm is a critical optimal value that strikes a balance between ensuring sufficient erosion resistance and maintaining high-resolution pattern transfer. To demonstrate the irreplaceability of this parameter window, an out-of-bounds comparative example is provided: if the spin-coating speed is reduced to 1500 rpm, due to insufficient centrifugal force, the photoresist cannot spread uniformly, resulting in an excessively thick photoresist layer (greater than 5 μm). When an excessively thick photoresist layer is immersed in the developer, the unexposed areas at the bottom layer are difficult to dissolve and penetrate completely, easily leading to incomplete development. This results in a large number of burrs and metal residues remaining on the edges of the final etched spiral electrode. These burrs can disrupt the nesting spacing of the equidistant concentric spirals and even cause short circuits between adjacent spirals. Conversely, if the spin coating speed is increased to 5000 rpm, the excessive centrifugal force will throw out a large amount of photoresist, resulting in an excessively thin photoresist layer (less than 1 μm). Such a thin photoresist layer is prone to localized damage or penetration by the etching solution during subsequent wet etching or resist removal, failing to provide effective masking protection. This causes the underlying platinum or conductive film to be mistakenly etched in non-target areas, directly disrupting the continuity of the spiral electrode. It should be understood that although the combination of 3000 rpm and 2 μm is preferred in this embodiment, in actual preparation, the rotation speed can be adjusted within a small range of 2800 rpm to 3200 rpm depending on the specific viscosity and solid content of the photoresist. As long as the thickness of the final photoresist layer is controlled between 1.8 μm and 2.2 μm, the process requirements can be met.

[0069] Regarding the heat treatment and exposure parameters, the pre-baking process is as follows: first, dry the photoresist layer at 65℃ for 5 minutes, then dry it at 95℃ for 15 minutes. The post-baking process is as follows: dry it at 150℃ for 10 minutes. The exposure dose is 50. These three sets of parameters are the core conditions for ensuring the correct crosslinking reaction and pattern transfer of the negative photoresist. Their setting logic and external risks are as follows:

[0070] First, the purpose of pre-baking is to gently evaporate the solvent in the photoresist, allowing it to solidify into a stable film without generating internal stress. The stepped heating strategy of 65℃ for 5 minutes followed by 95℃ for 15 minutes is used to avoid the rapid expansion and escape of the internal solvent caused by rapid high-temperature baking, which can lead to surface wrinkling and even microcracks in the photoresist. If an external contrast ratio is set, i.e., the pre-baking temperature is insufficient or the time is too short, a large amount of solvent will remain in the photoresist layer. During subsequent exposure, the bubbles generated by solvent evaporation will severely interfere with the uniformity of the optical path, resulting in incomplete cross-linking in the exposed area. After development, the edges of the spiral pattern will exhibit jagged wrinkles, failing to meet the stringent requirements for linewidth uniformity of equidistant concentric spirals.

[0071] Secondly, the exposure dose setting of 50 mJ / cm² is crucial in determining the final dimensional accuracy of the helical pattern. For negative photoresists, the exposure dose determines the cross-linking depth and sidewall steepness. 50 mJ / cm² ensures complete cross-linking of the photoresist in the mask's transparent area without significant lateral light scattering diffraction. If an out-of-bounds contrast ratio is set, i.e., overexposure (e.g., using an excessively high dose of 150 mJ / cm²), the strong lateral diffraction effect will cause partial cross-linking of the photoresist edges below the mask's shielded area. The helical pattern retained after development will expand, resulting in an actual linewidth greater than the designed linewidth. This linewidth expansion is fatal in equidistant concentric helical nested structures because the nesting spacing is already extremely small. Linewidth expansion will directly compress or even close the nesting gap, leading to misconnection of the inner ring ends or short circuits in the electrode spacing, completely destroying the decoupling sensing function.

[0072] Finally, the post-baking process involves drying at 150°C for 10 minutes to further solidify the exposed cross-linked photoresist network and resist erosion by the etching solution. If the external contrast ratio is set, i.e., the post-baking temperature or time is insufficient, the degree of cross-linking of the photoresist will be low. When immersed in the etching solution, it will soften and swell, failing to effectively prevent the etching solution from laterally penetrating the metal below the masked area. This penetrating effect leads to severe hollowing of the sidewalls of the spiral electrode, narrowing or even breakage of the inner ring connection, and an increase in the electrode spacing, ultimately causing the temperature sensing circuit to disconnect or the base value of the friction capacitance to severely decrease. Therefore, a post-baking at 150°C for 10 minutes is a necessary condition to ensure the fidelity of the etched pattern. It should be understood that the above parameters are preferred values ​​based on a specific type of negative photoresist. In other embodiments, if photoresists with different photosensitivity are used, the exposure dose and heat treatment time can be adjusted linearly accordingly, but the microscopic mechanism principle of stepped pre-baking to prevent wrinkling, moderate exposure to prevent diffraction, and sufficient post-baking to prevent penetrating must be followed.

[0073] This embodiment, through the above-mentioned refinement of the critical window of process parameters and the analysis of the boundary comparison, demonstrates from the perspective of microscopic chemical and physical reaction mechanisms that these parameters are not arbitrary conventional choices, but necessary technical means to serve the high-precision molding of equidistant concentric spiral nested structures, thus building a solid defensive line of defense for the creativity of process features.

[0074] Example 7: Based on the above embodiments, this embodiment further provides a specific application of multimodal flexible bionic electronic skin in the scenario of a robot's dexterous hand grasping fragile objects, so as to intuitively verify the functional breakthrough of the in-situ synchronous decoupled perception of the present invention and its great value in solving the pain points of commercial application.

[0075] Specifically, the application scenario is a robot's dexterous hand grasping a slippery and fragile glass containing hot water. This scenario highlights three core challenges in the field of tactile perception: excessive normal force can easily cause breakage, lateral shear force can easily lead to slippage, and thermal conduction temperature needs to be monitored, but the strain caused by the hand bending during grasping can easily interfere with temperature measurement. The electronic skin of this invention is attached to the dexterous fingertip and exhibits excellent multimodal decoupling perception capabilities during the grasping process.

[0076] At the moment of grasping, the fingertip contacts the outer wall of the glass, and the pressure sensing unit (composed of the third electrode 6 and the pressure-sensitive layer 7) first senses the magnitude of the normal contact force. When the pressure changes, the third electrode 6 squeezes the pressure-sensitive layer 7, causing a change in the conductive network composed of multi-walled carbon nanotubes inside the pressure-sensitive layer 7. The increase in contact points and the decrease in spacing cause a sharp drop in the macroscopic resistance value. The controller calculates the magnitude of the normal grip force in real time based on this change in resistance. This mechanism ensures that when a dexterous hand grasps a fragile glass, it can precisely apply a critical normal force that is just enough to overcome gravity without breaking it, thus preventing breakage. It should be understood that although this embodiment uses a glass as an example, this pressure sensing and anti-breakage mechanism is equally applicable to grasping other fragile items such as raw eggs and thin-walled porcelain.

[0077] When the cup tends to slide due to its slippery surface, the friction sensing unit (composed of the second electrode 4 and the PDMS medium 5) instantly senses the lateral shear force through changes in capacitance area, preventing slippage. When friction, i.e., lateral shear force, occurs, the two nested second electrodes 4, whose inner ends are not connected, slip relative to each other, causing a change in the area of ​​the effectively overlapping PDMS medium 5. The friction force is detected based on the change in capacitance. This detection mechanism based on area change makes the friction force signal almost unaffected by fluctuations in normal grip force. Even if a dexterous hand dynamically increases grip force to prevent slippage, the application of normal pressure mainly causes a slight compression of the electrode spacing. However, because the second electrode 4 has sufficient structural rigidity and the elastic deformation of the PDMS medium 5 is limited, the effect of spacing compression on capacitance is effectively suppressed, and the controller still receives a pure lateral slippage signal. Once a sudden change in capacitance area is detected, the controller immediately adjusts the gripping force in a closed loop or activates the anti-slip strategy, thereby achieving a stable grip on the slippery surface.

[0078] When the cup contains hot water, the temperature sensing unit (composed of the first electrode 2) senses the temperature conducted by heat. When the temperature changes, the resistance of the first electrode 2 changes, thus detecting the temperature change based on the resistance of the first electrode 2. More importantly, when the dexterous hand bends and grasps the curved surface of the glass, the electronic skin at the fingertips inevitably experiences stretching and bending strain. At this time, the equidistant concentric spiral nested structure used in the first electrode 2 transforms the external stretching or bending strain into the minute rotation and gap expansion of the spiral segments, rather than the direct axial stretching of the non-metallic conductor. This greatly suppresses resistance fluctuations caused by strain, ensuring that the strain from the hand's bending and grasping does not interfere with temperature measurement, achieving high-fidelity temperature sensing. This allows the robot to determine the temperature of the liquid inside the cup in real time, avoiding the risk of burns or adjusting the grasping strategy according to the temperature.

[0079] Ultimately, the three layers of detection signals from the temperature sensing unit, friction sensing unit, and pressure sensing unit are independently led out to an external controller, without interference. Based on these three in-situ synchronous and crosstalk-free decoupled signals, the controller constructs closed-loop control logic: the pressure signal maintains basic grip strength to prevent breakage, the friction signal triggers dynamic force amplification to prevent slippage, and the temperature signal provides environmental status warnings. This embodiment, through this highly representative grasping scenario, intuitively and rigorously verifies the breakthrough of this invention in achieving in-situ synchronous sensing and physical decoupling of three physical quantities—pressure, friction, and temperature—within a vertical heterogeneous integrated architecture. It not only solves the persistent problem of severe crosstalk between multiple physical signals in existing technologies but also demonstrates irreplaceable application value and extremely high visibility for infringement evidence collection in high-end commercial applications such as precision operation of intelligent robots and tactile restoration of bionic prosthetics.

[0080] It should be noted that any parts not disclosed or specifically described in this invention are existing technology or conventional configurations, and their specific structures and working principles will not be elaborated further. In this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0081] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be applied to various fields suitable for the present invention. Other modifications can be readily implemented by those skilled in the art. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and examples shown and described herein.

Claims

1. A multimodal flexible bionic electronic skin, characterized in that, Including the alignment settings from top to bottom: The temperature sensing unit includes a first flexible substrate layer and two equidistant concentric spiral first electrodes. Both first electrodes are connected to the upper end of the first flexible substrate layer and are nested together. The internal endpoints of the two first electrodes are connected to each other. The first electrodes are made of a conductive temperature-sensitive material. The friction sensing unit includes a second flexible substrate layer, two equidistant concentric spiral second electrodes, and a flexible elastic dielectric material. The two second electrodes are connected to the upper end of the second flexible substrate layer and are nested together. A flexible elastic dielectric material is provided between the two second electrodes to act as a capacitor, and the flexible elastic dielectric material connects the first flexible substrate layer and the second flexible substrate layer. The pressure sensing unit includes two equidistant concentric spiral third electrodes and a pressure-sensitive layer. Both third electrodes are connected to the lower end of the second flexible substrate layer and are nested together. The pressure-sensitive layer is located at the lower end of the two third electrodes. When the temperature changes, the resistance of the first electrode changes, and the temperature change is detected based on the resistance of the first electrode. When friction occurs, the distance between the two second electrodes changes, which in turn changes the area of ​​the effectively overlapping flexible elastic dielectric material. The friction force is detected based on the change in capacitance. When the pressure changes, the third electrode squeezes the pressure-sensitive layer, which changes the conductive network inside the pressure-sensitive layer, thereby causing a change in resistance. The pressure magnitude is detected based on the change in resistance.

2. The multimodal flexible bionic electronic skin according to claim 1, characterized in that, The method for fabricating the temperature sensing unit includes: A platinum thin film is formed on a first flexible substrate by magnetron sputtering, and then a negative photoresist is spin-coated on the platinum thin film to obtain a base element with a photoresist layer; The photoresist layer is flattened and pre-baked. The photoresist layer is exposed according to the photomask to obtain a preliminary element with two equidistant concentric spiral photoresist. The preliminary element is then immersed in the developer and cleaning solution in sequence. After the preliminary element is soaked, it is post-baked and then the platinum film in the preliminary element is etched to obtain a preliminary unit with two equidistant concentric spiral first electrodes, and the inner ring ends of the two first motors are connected to each other. The photoresist in the initial unit is removed by using an alkaline stripper to obtain the final temperature sensing unit.

3. The multimodal flexible bionic electronic skin according to claim 1, characterized in that, The method for preparing the friction sensing unit includes: A conductive layer is deposited on the upper surface of the second flexible substrate by magnetron sputtering, and then the conductive layer is etched to form a preliminary unit of two equidistant concentric spiral second electrodes, and the inner ring ends of the two second electrodes are not connected to each other. A flexible elastic dielectric material is coated onto the initial unit, and the flexible elastic dielectric material covers the second electrode, thereby forming a pressure sensing unit.

4. The multimodal flexible bionic electronic skin according to claim 1, characterized in that, The method for fabricating the pressure sensing unit includes: A conductive layer is deposited on the lower end face of the second flexible substrate by magnetron sputtering, and then a negative photoresist is spin-coated on the conductive layer to obtain a base element with a photoresist layer. The photoresist layer is flattened and pre-baked, and then exposed according to the photomask to obtain a preliminary element with two equidistant concentric spiral photoresist. The preliminary element is then immersed in the developer and cleaning solution in sequence. After the preliminary element is soaked, it is post-baked, then the conductive film in the preliminary element is etched, and then the photoresist is removed to obtain a preliminary unit with two equidistant concentric spiral electrodes. Photocurable flexible resin and multi-walled carbon nanotubes are mixed in a preset ratio, magnetically stirred, and then printed to obtain a sensing layer. The sensing layer is then soaked in isopropanol and cured to obtain a flexible piezoresistive sensing layer. The flexible piezoresistive sensing layer and electrodes are bonded and encapsulated to obtain a pressure sensing unit.

5. The multimodal flexible bionic electronic skin according to claim 2, characterized in that, The thickness of the photoresist layer is between 1.8 μm and 2.2 μm.

6. A multimodal flexible bionic electronic skin according to claim 2 or 4, characterized in that, The pre-baking process involves drying the photoresist layer at 65°C for 5 minutes, followed by drying at 95°C for 15 minutes. The post-baking process involves drying at 150°C for 10 minutes. The exposure dose is 50. .

7. The multimodal flexible bionic electronic skin according to claim 1, characterized in that, The thickness of the first electrode is between 180 nm and 220 nm, the thickness of the second electrode is between 15 μm and 25 μm, and the thickness of the third electrode is between 140 nm and 160 nm.

8. The multimodal flexible bionic electronic skin according to claim 1, characterized in that, The material of the first electrode is platinum.

9. The multimodal flexible bionic electronic skin according to claim 1, characterized in that, The first flexible substrate, the second flexible substrate, and the third flexible substrate are all made of polyimide material.

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