A pressure-temperature self-decoupled electronic skin and its preparation and material identification method

Abstract

This invention discloses a pressure-temperature self-decoupled electronic skin, its fabrication, and a material identification method. The electronic skin comprises multiple arrayed sensing units, including, from bottom to top, a flexible substrate, a heating functional layer, a pressure sensing layer, a temperature sensing layer, an encapsulation layer, and surface protrusion structures. The heating functional layer, pressure sensing layer, and temperature sensing layer each include patterned conductive lines and a flexible substrate. The surface protrusion structures are patterned, overlapping with the patterned conductive lines of the temperature sensing layer and the heating functional layer, and intersecting with the patterned conductive lines of the pressure sensing layer. Based on the heating function and monitoring the surface temperature change of the object under test, the material of the object can be identified. The electronic skin designed in this invention can achieve self-decoupling of temperature and pressure signals, and has advantages such as high sensitivity and high stability, enabling the identification of object materials. This electronic skin is lightweight, wearable, highly integrated, and can achieve large-area, high-resolution tactile sensing.

Description

Technical Field

[0001] This invention relates to the field of flexible sensor technology, specifically to a pressure-temperature self-decoupled electronic skin and its preparation and identification medium method. Background Technology

[0002] To mimic the tactile perception of human skin, electronic skin possesses multifunctional sensing capabilities, converting various external stimuli into electrical signals. This endows robotic hands with human-like tactile perception, making it a core component for intelligent sensing and human-computer interaction. It is widely used in smart healthcare, human-computer interaction, virtual reality, and other fields. With continuous technological advancements, society and industry have placed new demands on the functionality, ease of use, and comfort of electronic skin. On the one hand, electronic skin needs to achieve accurate sensing and decoupling of multiple stimulus signals; on the other hand, large-area, high-resolution sensing requires electronic skin with higher integration.

[0003] Pressure and temperature are important stimuli in tactile perception; however, most sensitive materials alter their signals in response to both. Decoupling pressure and temperature is key to accurate perception. Current methods primarily convert pressure and temperature stimuli into different forms of electrical signals, such as converting pressure into a capacitive signal and temperature into a resistive signal, thereby achieving decoupling between pressure and temperature.

[0004] While existing methods can decouple pressure and temperature, their complex structures and insufficient integration place high demands on backend signal processing equipment. Furthermore, the need for intelligent sensing requires electronic skins with richer functionality and more powerful recognition capabilities, such as object material identification. Current object material identification methods primarily employ multiple independent sensors to measure various physical quantities, resulting in high costs and low measurement efficiency. Summary of the Invention

[0005] The purpose of this invention is to provide a novel electronic skin with high sensitivity and high stability of pressure-temperature self-decoupling.

[0006] A pressure-temperature self-decoupled electronic skin includes multiple array-type sensing units, which, from bottom to top, include a flexible substrate, a heating functional layer, a pressure sensing layer, a temperature sensing layer, an encapsulation layer, and a surface protrusion structure.

[0007] The heating functional layer, pressure sensing layer, and temperature sensing layer include a substrate and patterned wires disposed on the substrate;

[0008] The surface protrusions are arranged in a patterned pattern, and the surface protrusions overlap with the patterned wires of the temperature sensing layer and the heating functional layer, and intersect with the patterned wires of the pressure sensing layer.

[0009] Preferably, the flexible substrate is made of a flexible polymer material, such as Ecoflex or PDMS, with a thickness of 50-500 micrometers.

[0010] Preferably, the patterned conductor adopts a serpentine, S-shaped, grid-shaped, or mesh structure.

[0011] Preferably, the thickness of the conductive material in the patterned wire is 5 nanometers to 100 micrometers, more preferably 25 nanometers to 300 nanometers. The patterned wire may use gold, silver, or graphene as the conductive material.

[0012] Preferably, the substrate of the heating functional layer, the pressure sensing layer, the temperature sensing layer, and the encapsulation layer are made of polyimide (PI), and the thickness of each layer is 1 micrometer to 300 micrometers, preferably 1 micrometer to 10 micrometers.

[0013] Preferably, the material of the protruding structure is a photocurable resin, a photocurable polymer, or a photoresist, with a thickness of 5 micrometers to 500 micrometers, more preferably 30 micrometers to 100 micrometers.

[0014] In this invention, the flexible substrate is a soft and elastic silicone rubber material. Relying on the flexibility of the substrate, when pressure is applied to the electronic skin sensing unit, the hard surface protrusion structure squeezes the patterned wires below. The pressure sensing layer wires intersect with the surface protrusion structure and are subjected to stretching and bending deformation, which changes the resistance. When the pressure is released, the flexible substrate quickly rebounds, and the shape and resistance of the wires are restored accordingly, thus enabling the function of sensing pressure.

[0015] The resistivity of a wire is related to temperature, thus enabling it to sense temperature.

[0016] Meanwhile, the patterned wires of the temperature sensing layer overlap with the surface protrusion structure, so the wires do not deform under pressure and their resistance remains almost unchanged. Therefore, the temperature sensing layer only responds to temperature signals, and the electronic skin has the function of pressure-temperature self-decoupling.

[0017] In this invention, the heating functional layer, pressure sensing layer, temperature sensing layer, and surface protrusion structure include multiple independent sensing units. The heating functional layer is a patterned conductor with two pin interfaces. For the temperature and pressure sensing layers, all units within the same layer share a single ground wire; therefore, N units require only N+1 pin interfaces to achieve independent signal sensing and output. By expanding the number of sensing units and increasing the measurement channels, multiple sensing units can operate simultaneously, enabling simultaneous multi-point measurement of pressure and temperature. Therefore, the electronic skin exhibits high integration and can be expanded with different numbers of sensing units to meet diverse sensing needs.

[0018] This invention also provides an application of pressure-temperature self-decoupled electronic skin in object material identification. The electronic skin measures the thermal conductivity, stiffness, and modulus of the object under test, thereby achieving material identification. When measuring the thermal conductivity of the object, a heating layer operates, and heat exchange occurs between the object and the electronic skin. The temperature change curve over time is measured by a temperature sensing layer, allowing estimation of the object's thermal conductivity and thus material identification. When measuring the stiffness and modulus of the object, the electronic skin is first fixed to a gripping device such as a flexible gripper. When the gripping device grasps the object, contact pressure is generated between the object and the electronic skin. The pressure change curve over time is measured by a pressure sensing layer, allowing estimation of the object's stiffness and modulus and thus material identification. Combining the thermal conductivity, stiffness, and modulus of the object allows for more accurate material identification.

[0019] The electronic skin of the present invention has good flexibility and high integration, and has a pressure-temperature self-decoupling function. It can expand multiple array units and independently output pressure and temperature signals, and has the advantages of high stability, high sensitivity and high linearity.

[0020] This invention also provides a method for fabricating pressure-temperature self-decoupled electronic skin, comprising the following steps:

[0021] (1) Electronic skin devices including a heating functional layer, a pressure sensing layer, a temperature sensing layer, an encapsulation layer, and surface protrusion structures are fabricated using micro-nano manufacturing technology;

[0022] (2) A flexible substrate of a specific thickness is prepared on a glass slide by spin coating and thermal curing using PDMS liquid prepolymer.

[0023] (3) The electronic skin device is transferred and bonded to a flexible substrate using water transfer printing technology, and finally the pressure-temperature self-decoupled electronic skin is obtained.

[0024] In step (1), the micro-nano manufacturing technology includes photolithography and development technology, metal coating technology, and polymer dry etching technology.

[0025] In step (2), the spin coating can obtain flexible substrates of different thicknesses by controlling the rotation speed and time, or a flexible substrate of a specific thickness can be prepared by using a mold.

[0026] In step (3), the water transfer printing technology flattens the released electronic skin device, the PI bottom layer and the PDMS bottom layer are completely adhered, and the surface protrusion structure side is exposed.

[0027] The specific steps of step (1) are as follows:

[0028] (1-1) An aluminum sacrificial layer is prepared by metal deposition on a silicon wafer.

[0029] (1-2) A PI liquid prepolymer is spin-coated onto an aluminum sacrificial layer and then thermo-cured to obtain a PI underlayer.

[0030] (1-3) After photolithography, development, metal coating and metal glass on the PI substrate, patterned wires of the heating functional layer are obtained.

[0031] (1-4) Repeat steps (1-2) and (1-3) to obtain the pressure sensing layer and temperature sensing layer in sequence.

[0032] (1-5) The PI prepolymer is spin-coated onto the temperature sensing layer and thermally cured to obtain the encapsulation layer, and the excess PI is etched by dry etching.

[0033] (1-6) A layer of photocurable resin is spin-coated onto the encapsulation layer, and after photolithography and development, a surface protrusion structure is obtained to form an electronic skin device.

[0034] (1-7) Electrolysis is used to release the electronic skin device from the silicon wafer.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] 1. The electronic skin of the present invention can achieve self-decoupling of pressure and temperature stimulation, and has the advantages of high sensitivity and high linearity.

[0037] 2. The electronic skin of the present invention can recognize the material of an object.

[0038] 3. The electronic skin of the present invention can integrate multiple sensing units, each of which independently senses pressure and temperature signals, thereby giving the electronic skin a large-area, high-density sensing capability.

[0039] 4. The electronic skin of the present invention is compatible with traditional microfabrication methods or semiconductor processes, and has high integration and few pins. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the overall pressure-temperature self-decoupling electronic skin according to an embodiment of the present invention;

[0041] Figure 2 This is a schematic diagram of a single unit structure of the electronic skin according to an embodiment of the present invention;

[0042] Figure 3 This is an amplified schematic diagram of the pressure-temperature self-decoupling principle in an embodiment of the present invention;

[0043] Figure 4 This is the signal response of pressure and temperature decoupling in an embodiment of the present invention;

[0044] Figure 5 The temperature sensing layer signal response is shown in the embodiment of the present invention when different objects are identified.

[0045] Figure 6 This is the signal response of the pressure sensing layer when identifying different objects in an embodiment of the present invention.

[0046] In the figure: 1-flexible substrate; 2-heating functional layer; 3-pressure sensing layer; 4-temperature sensing layer; 5-encapsulation layer; 6-surface protrusion structure, patterned wires 21 of heating functional layer, heating functional layer substrate 22, patterned wires 31 of pressure sensing layer, pressure sensing layer substrate 32, patterned wires 41 of temperature sensing layer, temperature sensing layer substrate 42. Detailed Implementation

[0047] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0048] like Figure 1 As shown, a 4×2 electronic skin array is composed of multiple layers stacked together, including, from bottom to top, a flexible substrate 1, a heating functional layer 2, a pressure sensing layer 3, a temperature sensing layer 4, an encapsulation layer 5, and a surface protrusion structure 6.

[0049] like Figure 2 As shown, the heating functional layer 2 includes patterned heating functional layer conductors 21 and a heating functional layer substrate 22; the pressure sensing layer 3 includes patterned pressure sensing layer conductors 31 and a pressure sensing layer substrate 32; and the temperature sensing layer 4 includes patterned temperature sensing layer conductors 41 and a temperature sensing layer substrate 42. In a single sensing unit, the surface protrusion structure 6 coincides with the patterned heating functional layer conductors 21 and the patterned temperature sensing layer conductors 41, and is perpendicular to the patterned pressure sensing layer conductors 31.

[0050] In this embodiment, the surface protrusion structure 6 and the patterned leads 21 of the heating functional layer, 31 of the pressure sensing layer, and 41 of the temperature sensing layer adopt a serpentine pattern. The flexible substrate 1 is made of a 150-micron-thick PDMS (polydimethylsiloxane) thin layer. The heating functional layer substrate 22, the pressure sensing layer substrate 32, the temperature sensing layer substrate 42, and the encapsulation layer 5 are made of PI (polyimide), each with a thickness of 3 microns. The patterned leads 21 of the heating functional layer, 31 of the pressure sensing layer, and 41 of the temperature sensing layer all adopt a chromium-gold double-layer metal structure, with gold of different thicknesses bonded to the substrate using 5 nanometers of chromium. The linewidth of the patterned lead 21 of the heating functional layer is 250 microns (to ensure uniform heating), and the gold thickness is 45 nanometers; the linewidth of the patterned leads 31 of the pressure sensing layer and 41 of the temperature sensing layer is 20 micrometers, and the gold thickness is 75 nanometers. The surface protrusion structure 6 is made of photocurable resin with a linewidth of 50 micrometers (slightly wider than the width of the patterned wires 41 in the temperature sensing layer to ensure pressure-temperature self-decoupling) and a thickness of 50 micrometers.

[0051] Figure 3 A magnified schematic diagram illustrating the pressure-temperature self-decoupling principle of the electronic skin is shown. Under pressure, the rigid surface protrusion structure 6 compresses the layers downwards. The patterned conductors 31 of the pressure-sensing layer, perpendicular to the surface protrusion structure 6, are stretched and bent as the flexible substrate 1 is recessed, resulting in a change in resistance. Simultaneously, the patterned conductors 21 of the heating function layer and the patterned conductors 41 of the temperature-sensing layer overlap with the surface protrusion structure 6, exhibiting minimal deformation under pressure and maintaining almost unchanged resistance. Therefore, the electronic skin possesses a pressure-temperature self-decoupling function.

[0052] Figure 4 The signal responses of the pressure sensing layer 3 and temperature sensing layer 4 of the electronic skin under pressure were demonstrated. As the pressure increases, the signal response of the pressure sensing layer 3 increases linearly, while the signal response of the temperature sensing layer 4 remains basically unchanged, thus achieving decoupling of the pressure and temperature signals.

[0053] Figure 5 This demonstrates the signal response of the temperature sensing layer 4 when the electronic skin identifies different objects. When the electronic skin comes into contact with objects of different materials, the heating functional layer 2 is energized and heats up. Different materials have different thermal conductivity coefficients, resulting in different temperature change trends. The temperature change process is tested through the temperature sensing layer 4, thereby enabling the identification of the object's material.

[0054] Figure 6This demonstrates the signal response of the pressure sensing layer when the electronic skin identifies different objects. The electronic skin is fixed to a gripping device such as a flexible gripper. When the object to be tested is grasped, the pressure sensing layer 3 responds to the contact pressure. Different materials have different stiffness and modulus, therefore the pressure changes differently with the gripping angle, thus enabling the identification of the object's material.

[0055] The following describes one method for preparing the pressure-temperature self-decoupled electronic skin of the present invention.

[0056] (1) Fabrication of electronic skin device (device functional layer)

[0057] A 100 nm aluminum metallization layer is deposited on a clean silicon wafer as a sacrificial layer. A PI prepolymer is spin-coated and thermally cured to prepare a 3 μm thick polymer substrate. Photolithography is performed on the PI substrate, and a 5 nm chromium layer (to enhance adhesion between the substrate and gold) and a 45 nm gold layer are deposited using metallization technology. Excess metal is then removed using acetone to form patterned wires. The spin-coating, photolithography, development, deposition, and lift-off steps are repeated, except that the gold thickness for the pressure sensing layer and temperature sensing layer is 75 nm.

[0058] Repeat the spin-coating steps described above to obtain a PI encapsulation layer with a thickness of 3 micrometers. A 100-nanometer aluminum protective layer is then prepared using photolithography, development, deposition, and lift-off steps. Excess PI is etched using plasma, and the aluminum protective layer is removed using an alkaline solution. A surface protrusion structure is then fabricated on the encapsulation layer surface using SU-8 material, with a linewidth of 50 micrometers and a thickness of 50 micrometers.

[0059] Finally, the silicon wafer is placed in an electrolytic cell to electrolyze the aluminum sacrificial layer at the bottom, thereby releasing the electronic skin device.

[0060] (2) Fabrication of flexible substrates

[0061] A flexible substrate with a thickness of 150 micrometers is obtained by spin-coating a layer of PDMS liquid prepolymer onto a glass slide and then thermally curing it. The spin-coating process can be used to obtain flexible substrates of different thicknesses by controlling the rotation speed and time, or a flexible substrate of a specific thickness can be prepared by using a mold.

[0062] (3) Transfer bonding

[0063] The released electronic skin device was flattened using the prepared PDMS, with the PI substrate and PDMS substrate completely adhered, and the surface protrusion structure exposed.

[0064] Example – Object Recognition

[0065] When the pressure-temperature self-decoupled electronic skin comes into contact with the object under test, the heating functional layer 2 activates, and the temperature of the object rises. At this time, the temperature sensing layer 4 responds to the temperature, and the trend of the temperature response signal over time is related to the thermal conductivity of the object. Therefore, a temperature-time curve is established, as shown below. Figure 5 As shown, it can achieve object material recognition.

[0066] The fabricated pressure-temperature self-decoupled electronic skin is fixed onto a general-purpose gripping device such as a flexible gripper. When the electronic skin approaches, contacts, and clamps the object under test, the pressure sensing layer 3 responds to the contact pressure. The pressure response signal changes with the angle of the gripping device. Since the angle of the gripping device is controlled by the gripping device drive motor, a curve showing the change of the pressure response signal with the rotation angle of the gripping device drive motor is established, such as... Figure 6 As shown, the trend of pressure response signal change is related to the stiffness and modulus of the object under test, thus enabling the identification of object material.

[0067] Combining the thermal conductivity, stiffness, and modulus of the object mentioned above can more accurately identify the material of the object.

Claims

1. A pressure-temperature self-decoupled electronic skin, characterized in that, It includes multiple array-type sensing units, which, from bottom to top, include a flexible substrate, a heating functional layer, a pressure sensing layer, a temperature sensing layer, an encapsulation layer, and a surface protrusion structure; The heating functional layer, pressure sensing layer, and temperature sensing layer include a substrate and patterned wires disposed on the substrate; The surface protrusions are arranged in a patterned pattern, and the surface protrusions overlap with the patterned wires of the temperature sensing layer and the heating functional layer, and intersect with the patterned wires of the pressure sensing layer.

2. The pressure-temperature self-decoupled electronic skin as described in claim 1, characterized in that, The flexible substrate is made of Ecoflex or PDMS.

3. The pressure-temperature self-decoupled electronic skin as described in claim 1, characterized in that, The patterned conductors adopt serpentine, S-shaped, grid-shaped, or mesh structures.

4. The pressure-temperature self-decoupled electronic skin as described in claim 1, characterized in that, The patterned wires are made of biocompatible conductive materials with a thickness of 5 nanometers to 100 micrometers.

5. The pressure-temperature self-decoupled electronic skin as described in claim 1, characterized in that, The base material of the heating functional layer, pressure sensing layer, and temperature sensing layer is PI, and its thickness is 1 micrometer to 300 micrometers.

6. The pressure-temperature self-decoupled electronic skin as described in claim 1, characterized in that, The encapsulation layer is made of PI and has a thickness of 1 micrometer to 300 micrometers.

7. The pressure-temperature self-decoupled electronic skin as described in claim 1, characterized in that, The material of the surface protrusion structure is a photocurable resin, a photocurable polymer, or a photoresist, and its thickness is 5 micrometers to 500 micrometers.

8. A method for preparing a pressure-temperature self-decoupled electronic skin as described in any one of claims 1-7, characterized in that, Includes the following steps: (1) Electronic skin devices including a heating functional layer, a pressure sensing layer, a temperature sensing layer, an encapsulation layer, and surface protrusion structures are fabricated using micro-nano manufacturing technology; (2) A flexible substrate was prepared on a glass slide by spin coating and thermal curing using PDMS liquid prepolymer; (3) The electronic skin device is transferred and bonded to a flexible substrate using water transfer printing technology, and finally the pressure-temperature self-decoupled electronic skin is obtained.

9. The method for preparing a pressure-temperature self-decoupled electronic skin as described in claim 8, characterized in that, The specific steps of step (1) are as follows: (1-1) An aluminum sacrificial layer is prepared by metal deposition on a silicon wafer; (1-2) A PI liquid prepolymer was spin-coated onto an aluminum sacrificial layer and then thermosetting to obtain a PI underlayer; (1-3) After photolithography, development, metal plating and metal stripping on the PI substrate, patterned conductive lines for the heating functional layer are obtained. (1-4) Repeat steps (1-2) and (1-3) to successively obtain the pressure sensing layer and the temperature sensing layer; (1-5) Spin-coating the PI prepolymer onto the temperature sensing layer and thermally curing it to obtain the encapsulation layer, and then dry etching the excess PI. (1-6) A layer of photocurable resin is spin-coated onto the encapsulation layer, and after photolithography and development, a surface protrusion structure is obtained to form an electronic skin device; (1-7) Electrolysis is used to release the electronic skin device from the silicon wafer.

10. The application of a pressure-temperature self-decoupled electronic skin as described in any one of claims 1-7 in object material recognition, characterized in that, The electronic skin is used to measure the thermal conductivity, stiffness, and modulus of the object under test, thereby enabling material identification of the object under test.

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