Flexible graphene joint sensor and method of making the same

Abstract

The application discloses a flexible graphene joint sensor and a preparation method thereof. The flexible graphene joint sensor comprises a first flexible layer, one side surface of which is a first surface; a graphene sensing unit arranged on the first surface; an extensible wire structure comprising a baseline layer and a conductive layer, the baseline layer being formed on at least part of the surface of the first surface, the conductive layer being formed on at least part of the surface of the baseline layer away from the first surface and connected with the graphene sensing unit; an external wire connected with the conductive layer of the extensible wire structure; and a second flexible layer, one side surface of which is a second adhesive surface, the second adhesive surface being arranged opposite to the first surface and covering the graphene sensing unit, the extensible wire structure, the first surface and part of the external wire. The flexible graphene joint sensor is an ultrathin flexible device, can be completely attached to the skin, is suitable for long-time wearing, and has the advantages of reliable connection and packaging mode and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of flexible mechanical sensors, in particular, the present application relates to a flexible graphene joint sensor and a preparation method thereof. BACKGROUND

[0002] Graphene is a single-atom layer structure material of carbon. Since it was discovered by researchers from graphite, graphene has been widely concerned due to its unique structure and excellent performance. It has very high electron mobility, ultra-high thermal conductivity, super strong mechanical properties and good optical transparency, etc. Good force-electric response makes graphene an ideal material for converting force / deformation signal and electrical signal, at the same time, the graphene thin layer structure and the natural flexibility and high strength performance make graphene an ideal flexible material. The combination of the above two excellent performances (electrical and mechanical properties) makes graphene widely used as a flexible sensing material.

[0003] Graphene joint sensor is a kind of sensor device containing graphene sensing unit and connecting wire, which converts the force / deformation generated by joint movement into resistance change signal in graphene through the force-electric conversion performance of graphene. The wire used in the traditional graphene joint sensor does not have ductility, and the line is difficult to completely fit the body surface, and the wearing comfort experience is poor. Therefore, the existing graphene joint sensor still needs to be improved. SUMMARY

[0004] The present application aims to solve at least one of the technical problems in the related art. To this end, one object of the present application is to propose a flexible graphene joint sensor and a preparation method thereof. The flexible graphene joint sensor is an ultra-thin flexible device that can completely fit the skin, is suitable for long-term wearing, and has advantages such as reliable connection and packaging mode.

[0005] In one aspect of the present application, a flexible graphene joint sensor is provided. According to an embodiment of the present application, the flexible graphene joint sensor comprises: a first flexible layer, one side surface of the first flexible layer being a first surface; a graphene sensing unit, the graphene sensing unit being arranged on the first surface; an extensible conductive wire structure, the extensible conductive wire structure comprising a base line layer and a conductive layer, the base line layer being formed on at least part of the surface of the first surface, the conductive layer being formed on at least part of the surface of the base line layer away from the first surface, the extensible conductive wire structure being connected with the graphene sensing unit; an external conductive wire, the external conductive wire being connected with the conductive layer in the extensible conductive wire structure; and a second flexible layer, one side surface of the second flexible layer being a second adhesive surface, the second adhesive surface being arranged opposite to the first surface and covering the graphene sensing unit, the extensible conductive wire structure, the first surface and part of the external conductive wire, the area of the second adhesive surface being greater than the area of the first surface.

[0006] According to the flexible graphene joint sensor of the embodiment of the present application, the extensible conductive wire structure adopts a skin electronic structure design and extends in a meandering manner on the first flexible layer and is connected with the external conductive wire at both ends of the first flexible layer. The extensible conductive wire structure is used at the joint part and provides the device with the ability of large deformation without damage. At the same time, the structure is thin and adheres to the skin, which is suitable for long-term wearing and has little inconvenience to the joint part. On the other hand, the two surfaces of the first and second flexible layers of the flexible graphene joint sensor of the present application press the graphene sensing unit and other components tightly and adhere to the adhesive surface as a whole. The first and second flexible layers tightly package each component, so that the graphene sensing unit and the extensible conductive wire structure can deform synchronously with the deformation of the flexible layer. In addition, by designing the area of the second adhesive surface to be greater than the area of the first surface, the second adhesive surface completely covers and exceeds the first surface after the device is packaged. Therefore, the second adhesive surface of the second flexible layer can face the skin, so that the device can be attached to the surface of the joint.

[0007] In addition, the flexible graphene joint sensor according to the above-mentioned embodiments of the present application can have the following additional technical features:

[0008] In some embodiments of the present application, the first surface is an adhesive surface.

[0009] In some embodiments of the present application, the base line layer is formed of polyimide (PI).

[0010] In some embodiments of the present application, the conductive layer comprises a chromium layer and a gold layer, the chromium layer being connected with the base line layer, and the gold layer being formed on the surface of the chromium layer away from the base line layer.

[0011] In some embodiments of the present application, the thickness of the chromium layer is 5-20 nm, and the thickness of the gold layer is 80-300 nm.

[0012] In some embodiments of the present application, the external connecting wire is formed by anisotropic conductive adhesive (ACF), conductive hot-press zebra paper, or silver.

[0013] In some embodiments of the present application, the graphene sensing unit includes a plurality of graphene sensing units.

[0014] In some embodiments of the present application, the graphene sensing unit includes two graphene units, and the two graphene units form a two-axis strain gauge.

[0015] In some embodiments of the present application, the graphene sensing unit includes three graphene units, and the three graphene units form a three-axis strain gauge.

[0016] In another aspect of the present application, a method for preparing the flexible graphene joint sensor of the above-mentioned embodiments is provided. According to an embodiment of the present application, the method comprises:

[0017] providing a substrate, sequentially forming a sacrificial layer, a baseline layer, and a conductive layer on the surface of the substrate, providing a photoresist mask with a predetermined pattern on the conductive layer, etching the conductive layer outside the predetermined pattern region to obtain a conductive layer with a predetermined pattern;

[0018] providing a flexible substrate, transferring the baseline layer and the conductive layer with a predetermined pattern to the surface of the flexible substrate, and etching the baseline layer not covered by the conductive layer with a predetermined pattern to obtain a stretchable wire structure;

[0019] providing a graphene sensing unit at a reserved position on the surface of the flexible substrate, connecting the stretchable wire structure with the graphene sensing unit and the external connecting wire;

[0020] covering the second adhesive surface of the second flexible layer to the graphene sensing unit, the stretchable wire structure, and part of the external connecting wire to obtain the flexible graphene joint sensor.

[0021] Therefore, the method is simple, efficient, and operable. The flexible graphene joint sensor prepared by the method can be completely attached to the skin, is suitable for long-term wearing, and has the advantages of reliable connection and packaging mode, etc.

[0022] In addition, the method for preparing the flexible graphene joint sensor according to the above-mentioned embodiments of the present application can also have the following additional technical features:

[0023] In some embodiments of the present application, after the formation of the sacrificial layer, the resultant product is heated to 100-115℃ for 5-10min, then heated to 150-155℃ for 5-8min, and then heated to 180-190℃ for 10-15min, and then the resultant product is cooled to solidify the sacrificial layer.

[0024] In some embodiments of the present application, after the formation of the base layer, the resultant product is heated to 80-90℃ for 10-15min, then heated to 120-130℃ for 30-35min, then heated to 150-160℃ for 30-35min, then heated to 200-210℃ for 30-35min, and then heated to 250-260℃ for 30-40min, and then the resultant product is cooled to solidify the base layer.

[0025] In some embodiments of the present application, the base layer not covered by the conductive layer with a predetermined pattern is etched by a reactive ion etching (RIE) method, and the process parameters of the reactive ion etching method include: oxygen flow rate of 15-30sccm, radio frequency power of 100-150W, and air pressure of 10-30Pa.

[0026] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0027] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the following description, taken in conjunction with the accompanying drawings, in which:

[0028] Figure 1 is a structural schematic diagram of a flexible graphene joint sensor according to an embodiment of the present application;

[0029] Figure 2 is a structural schematic diagram of another view of a flexible graphene joint sensor according to an embodiment of the present application;

[0030] Figure 3 is a structural schematic diagram of a flexible graphene joint sensor according to another embodiment of the present application;

[0031] Figure 4 is a structural schematic diagram of a flexible graphene joint sensor according to yet another embodiment of the present application. DETAILED DESCRIPTION

[0032] Hereinafter, an embodiment of the present application will be described in detail with reference to the drawings, wherein the same or similar components are denoted by the same or similar reference numerals throughout the drawings. Where a specific technique or condition is not mentioned in the embodiment, the technique or condition described in the literature or the product manual is used. Where a manufacturer of a reagent or instrument is not mentioned, a general product available on the market is used.

[0033] In the description of the present application, it is understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are used only for the purpose of facilitating the description of the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be construed as limiting the present application.

[0034] In addition, the terms "first", "second", "third" and the like are used only for the purpose of description, and cannot be construed as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Therefore, the features defined as "first", "second", "third" and the like can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise explicitly specified.

[0035] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connecting", "fixing" and the like should be interpreted broadly, for example, can be fixed connection, can be detachable connection, or can be integrated; can be mechanical connection, or can be electrical connection; can be directly connected, or can be indirectly connected through an intermediate medium; can be the internal communication of two elements or the interaction relationship between two elements, unless otherwise explicitly limited. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0036] In the present application, unless otherwise explicitly specified and limited, the first feature "on" or "under" the second feature can be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature "above", "over" and "on" the second feature can be that the first feature is directly above or obliquely above the second feature, or only indicates that the horizontal height of the first feature is higher than that of the second feature. The first feature "below", "under" and "under" the second feature can be that the first feature is directly below or obliquely below the second feature, or only indicates that the horizontal height of the first feature is less than that of the second feature.

[0037] In one aspect of the present application, the present application provides a flexible graphene joint sensor. According to an embodiment of the present application, referring to Figure 1 and 2 the flexible graphene joint sensor comprises a first flexible layer 100, a graphene sensing unit 200, an extensible wire structure 300, an external wire 400 and a second flexible layer 500. The first flexible layer 100 has a first surface on one side thereof; the graphene sensing unit 200 is arranged on the first surface; the extensible wire structure 300 comprises a base layer 310 and a conductive layer 320, the base layer 310 is formed on at least part of the first surface, the conductive layer 320 is formed on at least part of the surface of the base layer 310 away from the first surface, and the extensible wire structure 300 is connected to the graphene sensing unit 200; the external wire 400 is connected to the conductive layer 320 of the extensible wire structure 300; the second flexible layer 500 has a second adhesive surface on one side thereof, the second adhesive surface is arranged opposite to the first surface and covers the graphene sensing unit 200, the extensible wire structure 300, the first surface and part of the external wire 400, and the area of the second adhesive surface is greater than that of the first surface.

[0038] The flexible graphene joint sensor according to the embodiment of the present application is described in further detail below.

[0039] According to the embodiment of the present application, the specific types of the first flexible layer 100 and the second flexible layer 500 are not particularly limited and common flexible materials in the art can be used. In some embodiments of the present application, the first surface of the first flexible layer 100 is also an adhesive surface, and the adhesive surface and the second adhesive surface of the second flexible layer 500 can be obtained by applying an adhesive commonly used in the art on one side of a flexible material commonly used in the art. The first flexible layer 100 and the second flexible layer 500 both have adhesive surfaces, which can further improve the packaging effect of the product.

[0040] According to the embodiment of the present application, the base layer 310 can be formed of polyimide (PI) and serves to support the conductive layer 320.

[0041] According to the embodiment of the present application, the conductive layer 320 comprises a chromium layer and a gold layer, the chromium layer is connected to the base layer 310, and the gold layer is formed on the surface of the chromium layer away from the base layer 310. The conductive layer 320 comprises a lower chromium layer and an upper gold layer, and the chromium layer is in direct contact with the base layer 310, thereby further improving the adhesion between the conductive layer 320 and the base layer 310 while ensuring the conductivity of the conductive layer 320.

[0042] According to an embodiment of the present application, the thickness of the chromium layer can be 5-20 nm (e.g. 5 nm, 10 nm, 15 nm, 20 nm, etc.), and the thickness of the gold layer can be 80-300 nm (e.g. 80 nm, 120 nm, 160 nm, 200 nm, 250 nm, 300 nm, etc.). In this way, the conductivity of the conductive layer 320 and the adhesion between the conductive layer 320 and the baseline layer 310 can be further improved.

[0043] According to an embodiment of the present application, the external connecting wire 400 can be formed of anisotropic conductive adhesive (ACF), conductive hot-press zebra paper or silver. That is, the external connecting wire 400 can be an ACF wire or a conductive hot-press zebra paper or a silver wire. When the external connecting wire 400 is an ACF wire or a conductive hot-press zebra paper, the stretchable wire structure 300 can be connected to the ACF wire or the conductive hot-press zebra paper by a hot-press method; when the external connecting wire 400 is a silver wire, the stretchable wire structure 300 can be connected to the ACF wire by using silver glue.

[0044] According to an embodiment of the present application, the graphene sensing unit can include a plurality of graphene sensing units. In this way, a plurality of graphene sensing units can be arranged to form a strain rosette, so as to obtain more abundant strain information.

[0045] According to an embodiment of the present application, referring to Figure 3 The graphene sensing unit 200 can include two graphene sensing units 200, and the two graphene sensing units 200 form a two-axis strain rosette. In the two-axis strain rosette, the included angle between the two graphene sensing units 200 can be 90°, etc.

[0046] According to an embodiment of the present application, referring to Figure 4 The graphene sensing unit 200 can include three graphene sensing units 200, and the three graphene sensing units 200 form a three-axis strain rosette. In the three-axis strain rosette, the included angle between the three graphene sensing units 200 can be 45°, 60°, etc. The magnitude and direction of the principal strain can be calculated from the strain information on the three graphene sensing units 200 by using the three-axis strain rosette.

[0047] In another aspect of the present application, the present application provides a method for manufacturing the flexible graphene joint sensor of the above-mentioned embodiments. According to an embodiment of the present application, the method comprises:

[0048] (1) providing a substrate, sequentially forming a sacrificial layer, a baseline layer and a conductive layer on the surface of the substrate, disposing a photoresist mask having a predetermined pattern on the conductive layer, etching the conductive layer outside the predetermined pattern region, so as to obtain a conductive layer having a predetermined pattern.

[0049] According to the embodiments of the present application, the specific type of the substrate is not particularly limited, and for example, a silicon wafer or the like can be used. In some embodiments, the substrate can be cleaned with acetone, ethanol, deionized water, or the like before use.

[0050] According to the embodiments of the present application, the sacrificial layer can be formed by using a photoresist commonly used in the art, such as polymethyl methacrylate (PMMA).

[0051] According to the embodiments of the present application, after the photoresist and the base layer material are applied, the materials can be spun by using a spin coater, and then subsequent processing can be performed.

[0052] According to the embodiments of the present application, after the sacrificial layer is formed, the resulting product can be heated to 100-115°C for 5-10 min, then heated to 150-155°C for 5-8 min, and then heated to 180-190°C for 10-15 min, and then the resulting product is cooled, so as to solidify the sacrificial layer and reduce the stress in the sacrificial layer.

[0053] According to the embodiments of the present application, after the base layer is formed, the resulting product can be heated to 80-90°C for 10-15 min, then heated to 120-130°C for 30-35 min, then heated to 150-160°C for 30-35 min, then heated to 200-210°C for 30-35 min, and then heated to 250-260°C for 30-40 min, and then the resulting product is cooled, so as to solidify the base layer and reduce the stress in the base layer.

[0054] According to the embodiments of the present application, the conductive layer can be obtained by using an electron beam evaporation device to evaporate a conductive layer material on the base layer.

[0055] According to the embodiments of the present application, the photoresist mask with a predetermined pattern can be prepared by the following method: designing a mask with a pattern of the stretchable wire structure, and using a photolithography development method to transfer the pattern on the mask to the photoresist, so as to obtain a photoresist mask with a predetermined pattern. Further, a wet etching method is used to etch the conductive layer outside the pattern area of the photoresist mask, so as to obtain a conductive layer with a predetermined pattern.

[0056] (2) providing a flexible substrate, transferring the base layer and the conductive layer with a predetermined pattern to the surface of the flexible substrate, and etching the base layer not covered by the conductive layer with a predetermined pattern, so as to obtain a stretchable wire structure.

[0057] According to the embodiment of the present application, the baseline layer not covered by the conductive layer with the predetermined pattern can be etched by a reactive ion etching method, and the process parameters of the reactive ion etching method include: oxygen flow rate of 15-30 sccm, radio frequency power of 100-150 W, and air pressure of 10-30 Pa.

[0058] (3) The graphene sensing unit is arranged at the reserved position of the surface of the flexible substrate, and the extensible wire structure is connected with the graphene sensor and the external wire.

[0059] According to the embodiment of the present application, when the external wire is an ACF wire or a conductive thermal compression zebra paper, the extensible wire structure can be connected with the ACF wire or the conductive thermal compression zebra paper by thermal compression; when the external wire is a silver wire, the extensible wire structure can be connected with the ACF wire by silver glue.

[0060] (4) The second adhesive surface of the second flexible layer is covered to the graphene sensing unit, the extensible wire structure and part of the external wire to obtain the flexible graphene joint sensor.

[0061] Here, it should be noted that in the flexible graphene joint sensor of the present application, one side surface of the first flexible layer can be an adhesive surface or not. When the one side surface of the first flexible layer is not an adhesive surface, the first flexible layer can directly use the above flexible substrate to obtain the flexible graphene joint sensor product. When the one side surface of the first flexible layer is an adhesive surface, the above flexible substrate can be removed, and a flexible layer with an adhesive surface is provided as the first flexible layer, and the adhesive surface of the first flexible layer is covered to the second adhesive surface to obtain the flexible graphene joint sensor product.

[0062] The present application will be described below with reference to specific examples, and it should be noted that these examples are merely descriptive and do not limit the present application in any way.

[0063] Example 1

[0064] (1) A PMMA / Si Wafer bottom substrate is provided.

[0065] (a) The silicon wafer is first cleaned with an organic solution (first use acetone solution, then use ethanol solution, each for 10 minutes in a 70-degree Celsius water bath, and then rinse with deionized water).

[0066] (b) Coating PMMA on the silicon wafer, using spin coater to spin PMMA (400 rpm for 30 s + 4500 rpm for 30 s), and obtaining PMMA sacrificial layer after curing. The curing process is as follows: heating to 110-115 °C for 5-10 min, continuously heating to 150-155 °C for 5-8 min, continuously heating to 180-190 °C for 10-15 min, and naturally cooling to room temperature for 50-60 min to reduce the stress in the PMMA layer.

[0067] (2) Forming baseline layer PI on the PMMA / Si Wafer substrate.

[0068] (c) Spinning polyimide material on the PMMA sacrificial layer, using spin coater to spin PI (400 rpm for 30 s + 4500 rpm for 30 s), and obtaining polyimide layer after curing. The curing process is as follows: heating to 80-90 °C for 10-15 min, continuously heating to 120-130 °C for 30-35 min, continuously heating to 150-160 °C for 30-35 min, continuously heating to 200-210 °C for 30-35 min, continuously heating to 250-260 °C for 30-40 min, and naturally cooling for 40-60 min to reduce the stress in the polyimide layer.

[0069] (3) Forming conductive layer of stretchable wire structure on the baseline layer PI.

[0070] (d) Evaporating Cr / Au layer on the surface of the device using electron beam evaporation equipment, wherein Cr is in the lower layer and Au is in the upper layer.

[0071] (e) Designing mask plate of stretchable wire pattern, and using photolithography development method to transfer the pattern on the mask plate to photoresist to form mask pattern of stretchable wire.

[0072] (f) Using wet etching method to etch Cr / Au outside the photoresist mask pattern area, and forming Cr / Au wire structure after removing the photoresist.

[0073] (4) Providing a flexible substrate, and transferring the baseline layer and the conductive layer of stretchable wire to the flexible substrate (such as PDMS, hydrogel, etc.).

[0074] (5) Using reactive ion etching (RIE) method to etch PI in the area not covered by the conductive layer of stretchable wire (conditions: oxygen flow rate 15-30 sccm, radio frequency power 100-150 W, and gas pressure 10-30 Pa).

[0075] (6) The extendable conductive wire is connected to the external conductive wire through the port on the two sides of the flexible substrate. The external conductive wire can be ACF wire or conductive thermal pressure zebra paper or silver wire. If ACF wire or conductive thermal pressure zebra paper is used, the extendable conductive wire and the ACF wire or conductive thermal pressure zebra paper are connected by thermal pressure method; if silver wire is used, the extendable conductive wire and the silver wire are connected by silver glue.

[0076] (7) The graphene sensing unit is placed in the center of the reserved position on the flexible substrate, and the two ends of the graphene sensing unit are connected to the conductive layer of the extendable conductive wire by silver glue, so that the two are connected.

[0077] (8) The flexible layer (the second flexible layer, which can be a dressing composed of polyurethane film and acrylic adhesive) completely covers and exceeds the range of the flexible substrate, and the side of the second flexible layer facing the flexible substrate is adhesive, so as to stick the extendable conductive wire and the graphene sensing unit from the flexible substrate, and then a flexible layer (the first flexible layer) is further covered on the area of the second flexible layer where the extendable conductive wire and the graphene sensing unit are located, and the adhesive side faces the above area, so as to encapsulate the above area and tightly stick the extendable conductive wire and the graphene sensing unit between the two flexible covering layers. At the same time, since the covering area of the second flexible layer is larger than that of the first flexible layer, the adhesive side of the second flexible layer can face the skin, so as to realize the adhesion of the device on the surface of the joint.

[0078] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, different embodiments or examples described in the present specification and the features of different embodiments or examples can be combined and combined by those skilled in the art without contradiction.

[0079] Although the embodiments of the present application have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. A method for preparing a flexible graphene joint sensor, characterized in that, Flexible graphene joint sensors include: A first flexible layer, wherein one side surface of the first flexible layer is a first surface, and the first surface is an adhesive surface; A graphene sensing unit, wherein the graphene sensing unit is disposed on the first surface; A stretchable wire structure includes a baseline layer and a conductive layer, the baseline layer being formed on at least a portion of the surface of the first surface, and the conductive layer being formed on at least a portion of the surface of the baseline layer away from the first surface, the stretchable wire structure being connected to the graphene sensing unit. An external wire, which is connected to the conductive layer in the extendable wire structure; The second flexible layer has a second adhesive surface on one side. The second adhesive surface is disposed opposite to the first surface and covers the graphene sensing unit, the stretchable wire structure, the first surface and part of the external wire. The area of ​​the second adhesive surface is larger than the area of ​​the first surface. The method for the flexible graphene joint sensor includes: A substrate is provided, and a sacrificial layer, a baseline layer and a conductive layer are sequentially formed on the surface of the substrate. A photoresist mask with a predetermined pattern is disposed on the conductive layer, and the conductive layer outside the predetermined pattern area is etched to obtain a conductive layer with a predetermined pattern. A flexible substrate is provided, the baseline layer and the conductive layer with a predetermined pattern are transferred onto the surface of the flexible substrate, and the portion of the baseline layer not covered by the conductive layer with the predetermined pattern is etched to obtain a stretchable wire structure. A graphene sensing unit is disposed at a reserved position on the surface of the flexible substrate, and the stretchable wire structure is connected to the graphene sensing unit and the external wire. The flexible graphene joint sensor is obtained by covering the second adhesive surface of the second flexible layer onto the graphene sensing unit, the stretchable wire structure, and part of the external wire.

2. The method according to claim 1, characterized in that, The baseline layer is formed of polyimide.

3. The method according to claim 1, characterized in that, The conductive layer includes a chromium layer and a gold layer, the chromium layer being connected to the baseline layer, and the gold layer being formed on the surface of the chromium layer away from the baseline layer.

4. The method according to claim 3, characterized in that, The thickness of the chromium layer is 5~20 nm, and the thickness of the gold layer is 80~300 nm.

5. The method according to claim 1, characterized in that, The external conductor is formed of anisotropic conductive adhesive, conductive hot-pressed zebra paper, or silver.

6. The method according to claim 1, wherein the graphene sensing unit comprises a plurality of units.

7. The method according to claim 6, wherein the graphene sensing unit comprises two units, and the two graphene sensing units form a biaxial strain rosette.

8. The method according to claim 6, wherein the graphene sensing unit comprises three units, and the three graphene sensing units form a triaxial strain rosette.

9. The method according to claim 1, characterized in that, After the sacrificial layer is formed, the resulting product is heated to 100~115 °C and held for 5~10 min, then heated to 150~155 °C and held for 5~8 min, then heated to 180~190 °C and held for 10~15 min, and then the resulting product is cooled to allow the sacrificial layer to solidify.

10. The method according to claim 9, characterized in that, After the baseline layer is formed, the resulting product is heated to 80-90 °C and held for 10-15 min, then heated to 120-130 °C and held for 30-35 min, then heated to 150-160 °C and held for 30-35 min, then heated to 200-210 °C and held for 30-35 min, then heated to 250-260 °C and held for 30-40 min. The resulting product is then cooled to allow the baseline layer to solidify.

11. The method according to claim 9, characterized in that, The baseline layer, which is not covered by the conductive layer with the predetermined pattern, is etched by reactive ion etching. The process parameters of the reactive ion etching method include: oxygen flow rate of 15~30 sccm, radio frequency power of 100~150 W, and gas pressure of 10~30 Pa.

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