Multilayer Flexible Electronic Devices, Their Fabrication Methods and Applications

Abstract

This application relates to the field of flexible electronics technology, and more particularly to multilayer flexible electronic devices, their fabrication methods, and applications. The fabrication method includes: providing a film unit, comprising a flexible film and a circuit bonded to a surface of the flexible film, wherein the surface of the film unit with the circuit bonded is designated as a first surface, and the surface opposite to the first surface is designated as a second surface; immersing the film unit and a first substrate in a liquid, performing a first bonding treatment on the first surface and the surface of the first substrate, and removing the film unit from the liquid to obtain a film composite unit; using the first surface of the film unit that has not undergone the first bonding treatment as a front surface, and the second surface of the film composite unit as a rear surface, performing a second bonding treatment on the front and rear surfaces; peeling the first substrate in the film composite unit after the second bonding treatment, so that the first surface in the film composite unit forms a new front surface; repeating the second bonding treatment and peeling treatment steps to obtain a multilayer flexible electronic device.

Description

Technical Field

[0001] This application relates to the field of flexible electronics technology, and in particular to multilayer flexible electronic devices, their fabrication methods, and applications. Background Technology

[0002] Flexible electronics technology has gradually expanded from early applications in flexible displays and sensors to various complex applications such as human implant interfaces, wearable systems, soft robots, and human-computer interaction. Whether it's a flexible system attached to or implanted into the human body and tightly coupled with biological tissue, or a flexible electronic system used in complex curved surfaces or confined spaces, it requires high functional density and high integration within a limited volume. High-density fabrication and high volume utilization are the key challenges. To address this, flexible electronic systems have gradually evolved from two-dimensional planar architectures to three-dimensional structures of multilayer thin films stacked vertically. This allows for the three-dimensional integration of wiring and functional units, significantly improving volume utilization. Conductive layers are separated by insulating layers, allowing each conductive layer to function independently without being affected by adjacent layers, resulting in a high channel count, i.e., high throughput. Traditional microfabrication processes can construct multilayer flexible electronic systems by sequentially performing spin-coating and cross-linking of insulating elastomers, photolithographic patterning, and metal deposition, repeating the process. While this method produces products with ideal performance, its manufacturing process is highly complex, heavily reliant on cleanroom conditions and photolithography equipment, and has a long process cycle and high cost, making it difficult to scale up to high-throughput, low-cost mass manufacturing.

[0003] Another technical solution borrows from printed circuit board technology, providing several two-dimensional thin films with patterned circuits, and then laminating these films sequentially, gradually increasing their thickness to construct a three-dimensional stacked structure. However, when applying this technology to flexible electronic systems, reliable pickup, transfer, and interlayer assembly of ultrathin organic films are required, which is mechanically extremely challenging. Since the thickness of ultrathin organic films is often ≤10 µm, if ultrathin plastic films of plastic material are selected, they are prone to curling or breaking during peeling and transfer; if elastomer films of elastic material are selected, their softness and low bending stiffness often lead to collapse, curling, and self-adhesion after detaching from the supporting substrate. Even with the introduction of flexible support rings, it is difficult to avoid failures during the transfer process. Elastomer films are also prone to forming a large number of air bubbles between layers during lamination. These problems can lead to damage or deformation of the ultrathin organic films, and the circuits will also suffer from pattern distortion and loss of precision, ultimately resulting in low interlayer assembly yield and insufficient fidelity in shape, size, and structure, which seriously restricts the practical application of three-dimensional flexible electronic systems.

[0004] It is evident that the pickup, transfer, and interlayer assembly of such ultrathin organic films present numerous challenges. Therefore, achieving controllable pickup and stable interlayer bonding of ultrathin organic films remains a key technological bottleneck in the lamination process for fabricating high-functional-density flexible electronic systems. Summary of the Invention

[0005] The purpose of this application is to provide multilayer flexible electronic devices, their fabrication methods and applications, aiming to solve the problems of high fabrication difficulty and poor product quality of multilayer flexible electronic devices in the prior art.

[0006] To achieve the above-mentioned objectives, the technical solution adopted in this application is as follows:

[0007] In a first aspect, this application provides a method for fabricating a multilayer flexible electronic device, comprising the following steps:

[0008] A membrane unit is provided, including a flexible membrane and a circuit bonded to a surface of the flexible membrane. The surface of the membrane unit with the circuit bonded is referred to as the first surface, and the surface opposite to the first surface is referred to as the second surface.

[0009] The membrane unit and the first substrate are immersed in a liquid, the first surface and the surface of the first substrate are subjected to a first bonding treatment, and then the membrane composite unit is removed from the liquid.

[0010] Using the first surface of the membrane unit that has not undergone the first bonding process as the front surface and the second surface of the membrane composite unit as the rear surface, the front surface and the rear surface are bonded together in a second bonding process.

[0011] The first substrate in the second laminated membrane composite unit is peeled off to form a new front surface on the first surface of the membrane composite unit.

[0012] Repeat the second bonding and peeling process to obtain a multilayer flexible electronic device.

[0013] The method described in this application fabricates multilayer flexible electronic devices by laminating a flexible film after processing it. Firstly, the method of fabricating the film composite unit through a first bonding process in a liquid not only reduces the formation of air bubbles between the film unit and the first substrate, but also, with the first substrate acting as a temporary support, effectively mitigates the phenomenon of flexible film wrinkling or damage during the transfer of the film unit to the surface of the first substrate. Both of these advantages contribute to the stability of the flexible film's shape, resulting in a stable structure for the fabricated multilayer flexible electronic device. Furthermore, it facilitates the stability of the circuitry on the flexible film surface, exhibiting a low rate of dimensional change and high fidelity during transfer. This ensures high consistency of the high-precision circuitry within each film composite unit, significantly improving upon the defects of using flexible thin films in existing lamination methods and addressing the issues of circuit distortion and precision loss. Secondly, the combination of the first bonding process with a second bonding process and a peeling process promotes stable interlayer bonding between the film units. The first substrate can be released almost without damage during the peeling process, effectively improving the overall structural integrity and long-term stability of the multilayer flexible electronic device, which is beneficial for high-density integration. Furthermore, by fabricating film composite units in a liquid and assembling them through repeated second bonding and peeling processes, the complex processes such as photolithography, etching, or high-temperature treatments required by existing technologies are eliminated. This simplifies the process flow, significantly reduces the time required to fabricate devices with the same number of layers, and provides high stability and yield. The multilayer flexible electronic devices prepared using this method exhibit excellent mechanical stretchability, capable of withstanding significant tensile deformation while maintaining usable resistance. Moreover, their conductivity does not significantly decrease after repeated tensile deformation, and they demonstrate good long-term stability and reliability under dynamic operating environments.

[0014] Secondly, this application provides a multilayer flexible electronic device, which is prepared by the above-described preparation method of this application.

[0015] The multilayer flexible electronic device of this application has high structural stability and high electrical stability. It can not only withstand large tensile deformation while the resistance is still within the usable range, but also the conductivity does not significantly decay after repeated tensile deformation. It has good long-term stability and reliability in dynamic working environment.

[0016] Thirdly, this application provides an application of a multilayer flexible electronic device, wherein the multilayer flexible electronic device prepared by the above-described preparation method is applied to at least one of wearable flexible devices, implantable physiological devices, brain-computer interfaces, flexible electronic packaging, and flexible electronic integration.

[0017] Because the multilayer flexible electronic devices prepared by the above-mentioned method have advantages such as flexible conductivity, ultrathinness, high density, high volume utilization, and multilayer integration, they can be applied in wearable flexible devices, implantable physiological devices, brain-computer interfaces, flexible electronic packaging, flexible electronic integration and other equipment or processes. Furthermore, they have significant advantages and broad application prospects in cutting-edge fields such as advanced medicine, neurorehabilitation, functional reconstruction and intelligent diagnosis and treatment. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of this application, 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 this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram illustrating the fracture or collapse of the two ultrathin films in Comparative Example 1 and Comparative Example 2 during peeling from the substrate. Figure 1 In Figure 'a', the diagram shows the peeling of the plastic ultrathin film in Comparative Example 1. Figure 1 b in the diagram is a schematic diagram of the elastic ultrafilm in Comparative Example 2 collapsing in water, collapsing in air, and curling into a bundle.

[0020] Figure 2 This is a schematic diagram of step S2 of Embodiment 1 of this application, in which the SEBS film is transferred to the carrier using water-based transfer technology;

[0021] Figure 3 This is a schematic diagram of steps S3 to S5 in Embodiment 1 of this application for constructing a multilayer flexible electronic device;

[0022] Figure 4 This is a schematic diagram illustrating the process and results of fabricating a multilayer flexible circuit, specifically a physiological electrode array, as described in Embodiment 1 of this application. Figure 4 In this context, 'a' represents the assembly process of the N-layer electrode array. Figure 4 In the diagram, b represents a ten-layer electrode array structure. Figure 4 In the image, 'c' represents a photograph of the front-end electrode points of the ten-layer electrode array.

[0023] Figure 5 This is a schematic diagram of the multilayer flexible circuit fabricated in this application, which constitutes a high-density physiological electrode array;

[0024] Figure 6 These are comparison diagrams of the membrane units of Example 1 and Comparative Example 3 before and after transfer in different media.

[0025] Figure 7This describes the number and diameter of interface bubbles in a 10 mm × 10 mm area after being transferred in different media in Example 1 and Comparative Example 3 of this application.

[0026] Figure 8 This refers to the ratio of the pattern geometric parameters of Embodiment 1 and Comparative Example 3 after transfer in different media to their original values ​​before transfer.

[0027] Figure 9 This refers to the energy required to separate the SEBS-SEBS interface and the SEBS-PDMS interface in Embodiment 1 of this application;

[0028] Figure 10 These are the interface separation results predicted by the mechanical model under different peeling conditions;

[0029] Figure 11 These are comparison diagrams of the peeling process under different peeling parameters in Examples 1 and 9;

[0030] Figure 12 The impedance and phase angle of the multilayer flexible circuit in Example 1 during 1000 tensile cycle tests;

[0031] Figure 13 This is a schematic diagram illustrating the movement of rats induced by electrical stimulation after the multilayer flexible circuit of Example 1 was implanted into the spinal cord. Figure 13 In the diagram, 'a' represents the electrode implantation schematic. Figure 13 b in the text refers to the selective induction of hindlimb movement in rats via electrical stimulation.

[0032] Figure 14 This is a schematic diagram of the overall process flow for the preparation of Example 1. Detailed Implementation

[0033] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0034] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0035] In this application, "at least one" means one or more, and "multiple" means two or more. "At least one of the following" or similar expressions mean any combination of these items, including any combination of single or multiple items.

[0036] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0037] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass in the embodiments of this application can be a well-known unit of mass in the chemical industry, such as µg, mg, g, or kg.

[0038] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, a first feature may also be referred to as a second feature, and similarly, a second feature may also be referred to as a first feature. Thus, a feature defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0039] The first aspect of this application provides a method for fabricating a multilayer flexible electronic device, comprising the following steps S10 to S50:

[0040] S10: Provide a membrane unit, including a flexible membrane and a circuit bonded to a surface of the flexible membrane, wherein the surface of the membrane unit with the circuit bonded is referred to as the first surface and the surface opposite to the first surface is referred to as the second surface.

[0041] S20: Immerse the membrane unit and the first substrate in the liquid, perform a first bonding process on the first surface and the surface of the first substrate, and remove them from the liquid to obtain the membrane composite unit;

[0042] S30: Using the first surface of the membrane unit that has not undergone the first bonding process as the front surface and the second surface of the membrane composite unit as the rear surface, perform a second bonding process on the front surface and the rear surface.

[0043] S40: The first substrate in the second laminated membrane composite unit is peeled off to form a new front surface on the first surface of the membrane composite unit.

[0044] S50: Repeat the second bonding and peeling process to obtain a multilayer flexible electronic device.

[0045] The method described in this application fabricates multilayer flexible electronic devices by laminating a flexible film after processing it. On one hand, the method of fabricating the film composite unit through a first bonding process in a liquid not only reduces the formation of air bubbles between the film unit and the first substrate, but also, with the first substrate acting as a temporary support, effectively mitigates the phenomenon of flexible film wrinkling or damage during the transfer of the film unit to the surface of the first substrate. Both of these advantages contribute to the stability of the flexible film's shape, resulting in a stable structure for the fabricated multilayer flexible electronic device. Furthermore, it facilitates the stability of the circuitry on the flexible film surface, exhibiting a low rate of dimensional change and high fidelity during transfer. This ensures high consistency of the high-precision circuitry within each film composite unit, significantly improving upon the defects of using flexible films in existing lamination methods and addressing the issues of circuit distortion and precision loss. On the other hand, the combination of the first bonding process with a second bonding process and a peeling process promotes stable interlayer bonding between the film units. The first substrate can be released almost without damage during the peeling process, effectively improving the overall structural integrity and long-term stability of the multilayer flexible electronic device, which is beneficial for high-density integration. Furthermore, by fabricating film composite units in a liquid and assembling them through repeated second bonding and peeling processes, the complex processes such as photolithography, etching, or high-temperature treatments required by existing technologies are eliminated. This simplifies the process flow, significantly reduces the time required to fabricate devices with the same number of layers, and provides high stability and yield. The multilayer flexible electronic devices prepared using this method exhibit excellent mechanical stretchability, capable of withstanding significant tensile deformation while maintaining usable resistance. Moreover, their conductivity does not significantly decrease after repeated tensile deformation, and they demonstrate good long-term stability and reliability under dynamic operating environments.

[0046] Step S10 is the step of providing membrane units by incorporating circuitry onto the surface of the flexible membrane.

[0047] In some embodiments, the flexible film contains an elastic material, including at least one of styrene-ethylene-butene-styrene block copolymer (SEBS), polyurethane (PU), polydimethylsiloxane (PDMS), and polyurethane acrylate (PUA). Flexible films made from these materials exhibit good stretchability and certain adhesive properties, making them suitable as flexible insulating layers in multilayer flexible electronic devices. These flexible films also possess good biocompatibility, enabling the fabricated multilayer flexible electronic devices to be widely used in wearable health monitoring, implantable electronic devices, and other fields. In the exemplary example, the block copolymer includes SEBS, which also possesses good self-healing properties. Therefore, in the subsequent second bonding process, adjacent SEBS film layers can spontaneously form a stable bonding interface after contact, allowing for timely repair of microcracks that may appear during significant deformation of the multilayer flexible electronic device.

[0048] In some embodiments, the thickness of the flexible film is 0.4 μm to 10 μm. In the example, it may include, but is not limited to, any value or any two values ​​of 0.4 μm, 1.0 μm, 2.5 μm, 5.0 μm, 7.5 μm, and 10 μm. Such a thin thickness is beneficial to improving the integration, volume utilization and functional density of multilayer flexible electronic devices. Moreover, such an ultrathin flexible film can still maintain shape stability in subsequent steps S20 to S50, which significantly improves the problems that are easy to occur when processing ultrathin flexible films in existing preparation methods.

[0049] In some embodiments, the method for preparing the flexible membrane in step S10 includes the following steps S11 to S12:

[0050] S11: Perform a first film-forming treatment on one side of the second substrate to form a sacrificial layer;

[0051] S12: Perform a second film-forming process on the surface of the sacrificial layer away from the second substrate to form a flexible film;

[0052] The sacrificial layer can dissolve in the liquid.

[0053] This fabrication method uses a second substrate to support the flexible membrane. Flexible membranes, especially ultrathin ones, are prone to deformation. The second substrate ensures the flexible membrane maintains its shape and structural stability before circuit bonding and subsequent immersion in a liquid, reducing problems such as collapse and self-adhesion caused by the characteristics of ultrathin flexible membranes. The sacrificial layer can dissolve during subsequent immersion in the liquid, releasing the flexible membrane for the subsequent first bonding process. It should be noted that the dissolution of the sacrificial layer in the liquid should be interpreted broadly, including physical dissolution, chemical reaction between the sacrificial layer and the liquid, or a combination of both, as long as the flexible membrane can be released in the liquid.

[0054] In some embodiments, the second substrate in step S11 includes at least one of glass, silicon wafer, sapphire, and polyethylene terephthalate, and may be glass. These second substrates have good structural stability and can support the flexible film. After supporting the flexible film and bonding the circuit, and after immersion in the liquid, they can be removed from the liquid after the sacrificial layer dissolves, and the second substrate can be reused. In an exemplary example, the thickness of the second substrate can be 0.3 mm to 5 mm. Before the first film formation process, a surface activation treatment, such as plasma treatment, can be performed to improve the adhesion between the sacrificial layer and the second substrate and maintain interface stability.

[0055] In some embodiments, the sacrificial layer contains at least one of sodium polystyrene sulfonate (PSSNa), polyvinyl alcohol (PVA), and polyvinylpyrrolidone (PVP), optionally PSSNa. These sacrificial layer materials exhibit good chemical stability to the second substrate and the flexible membrane, and are soluble in liquids such as water, ethanol, methanol, and isopropanol, allowing for near-undamaged release of the flexible membrane from the liquid. The first film-forming process may include spin coating and thermoforming. In an exemplary embodiment, PSSNa can be prepared into a solution with a concentration of 10 mg / mL to 150 mg / mL, then spin-coated onto the surface of the second substrate at a spin coating speed of 100 rpm to 3000 rpm, and finally annealed at 80°C to 200°C for 5 s to 120 s to form the sacrificial layer.

[0056] Step S12 further forms a flexible film through a second film-forming process. In some embodiments, the second film-forming process includes spin coating and thermoforming. In an exemplary example, the material contained in the flexible film can be prepared into a solution, such as a SEBS toluene solution with a concentration of 10 gm / mL to 200 gm / mL, and then spin-coated onto the surface of the sacrificial layer. The spin coating speed can be 100 rpm to 3000 rpm. Finally, it is cured at 80°C to 200°C for 1 min to 20 min to form a flexible film. The flexible film is laminated with the sacrificial layer and has a second substrate as a structural support to maintain shape stability.

[0057] Furthermore, the circuit formation method in step S10 can include, but is not limited to, vapor deposition. Vapor deposition facilitates a strong bond between the circuit and the flexible film and can also form various patterns, improving the functionality of the multilayer flexible electronic device. In the example, a metal functionalized pattern, such as at least one of gold, silver, and copper, can be thermally vapor-deposited at a rate of 0.005 nm / s to 0.05 nm / s using a mask to form a circuit.

[0058] In some embodiments, the thickness of the circuit is 10 nm to 300 nm, which may include, but is not limited to, any value or any two values ​​of 10 nm, 15 nm, 30 nm, 50 nm, 100 nm, 200 nm, and 300 nm. Circuits with these thicknesses can ensure conductivity continuity and maintain stable electrical performance under bending, stretching, and other deformations, which is beneficial to improving the volume utilization of the fabricated multilayer flexible electronic devices.

[0059] The circuit can be array-type, such as Figure 4 As shown, a small number of electrodes can be set on its edge; or as shown in the figure. Figure 5 As shown, high-density electrodes are set to improve the throughput of the final fabricated device.

[0060] Flexible films and circuits together form film units. The resulting multilayer flexible electronic devices are made by stacking these film units. Circuits are separated from each other by flexible films, and the circuits in each layer do not interfere with each other.

[0061] Step S20 is the first bonding process, which involves transferring the membrane unit to the surface of the first substrate. If the circuit does not cover the entire first surface, the first bonding process includes bonding the circuit to the first substrate and bonding the surface of the flexible membrane to the first substrate; if the circuit completely covers the entire first surface, the first bonding process involves bonding the circuit to the first substrate. In the example, the circuit is patterned and occupies a small area, allowing the surface of the flexible membrane to also bond to the first substrate, which helps reduce phenomena such as bubbles and wrinkles.

[0062] Please see Figure 2 , Figure 6 , Figure 7 and Figure 8 The method of performing the first bonding process in a liquid not only reduces the formation of air bubbles between the membrane unit and the first substrate, but also, with the first substrate acting as a temporary support, effectively mitigates the phenomenon of flexible membrane wrinkling or damage during the transfer of the membrane unit to the surface of the first substrate. In contrast, transferring and bonding in air inevitably leads to the formation of air bubbles between the two or deformation of the membrane unit, resulting in structural defects, circuit distortion, and loss of precision in the final stacked multilayer flexible electronic device.

[0063] In some embodiments, the first substrate contains at least one of polydimethylsiloxane (PDMS), polyethylene terephthalate (PET), and polytetrafluoroethylene (PTFE). These first substrates have good chemical stability to the membrane unit and a certain structural strength, and can serve as a temporary support carrier for the membrane unit. Moreover, the interfacial bonding force between the first substrate and the membrane unit is moderate, which allows it to maintain adhesion to the membrane unit during the transfer process. In the subsequent second bonding and peeling processes, this bonding force is lower than the bonding force between the two membrane units, so the impact on the membrane units that have already undergone the second bonding can be reduced while peeling off the first substrate.

[0064] In some embodiments, the thickness of the first substrate is 100 μm to 600 μm. This thickness range provides sufficient mechanical support during the first bonding process while minimizing damage to the membrane cells during subsequent peeling. The first substrate can be prepared by spin coating. In an exemplary embodiment, the PDMS base liquid and curing agent are mixed and stirred evenly at a mass ratio of 10:1, then spin-coated onto a glass substrate at a rotation speed of 100 rpm to 2000 rpm, cured at 80°C to 150°C for 1 min to 10 min, and finally peeled off from the glass substrate to obtain a self-supporting PDMS thick film.

[0065] In some embodiments, the liquid includes at least one of water, ethanol, methanol, and isopropanol. These liquids exhibit good chemical stability to the membrane unit and the first substrate, and facilitate the unfolding of the membrane unit and its bonding with the first substrate during the first bonding process, reducing air bubble residue. In an exemplary example, compared to bonding in air, this method of performing the first bonding process in a liquid reduces the number of air bubbles by approximately 96.7%, and the maximum bubble diameter is reduced from approximately 3 mm to 0.75 mm, significantly reducing the impact on the flexible membrane shape and circuit accuracy.

[0066] In some embodiments, when the membrane unit is bonded to a sacrificial layer on the surface of the second substrate, immersing the membrane unit in a liquid includes the following step S21:

[0067] S21: First, fix the edge of the flexible membrane in the membrane unit, then immerse the membrane unit in the liquid so that the sacrificial layer dissolves in the liquid, and obtain a membrane unit with fixed edge.

[0068] Since ultrathin flexible membranes are extremely prone to self-adhesion, wrinkles, curling and damage, this step further restricts their degree of freedom by fixing the edges. In this way, during the dissolution of the sacrificial layer, phenomena such as collapse and curling caused by lack of support in the membrane unit can be effectively reduced.

[0069] In the example, the fixing process can involve attaching a frame, such as a polyethylene terephthalate (PET) frame, to the edge area of ​​the flexible membrane of the membrane unit and fixing it with tape. The tape can be polyimide (PI) tape. These materials have high chemical stability to the membrane unit. After the sacrificial layer dissolves, the membrane unit detaches from the second substrate. Although the membrane unit itself is flexible, it can still maintain a flat and smooth state due to the edge fixing process of the frame and tape. This is beneficial for reducing the generation of air bubbles and reducing wrinkles and damage during the subsequent first bonding process with the first substrate.

[0070] The first bonding process is carried out in a liquid, aligning and bonding the membrane unit to the first substrate. During this process, a very thin liquid layer exists on the surfaces of the membrane unit and the first substrate, acting as an adhesive to further enhance the bonding strength between the membrane unit and the first substrate through intermolecular forces. In the example, the first substrate has a large area, and its outline can encompass the membrane unit, allowing the entire membrane unit to remain flat and smoothly bonded, resulting in a membrane composite unit. After bonding, the membrane composite unit is removed from the liquid.

[0071] In some embodiments, after removing the membrane composite unit from the liquid, the process further includes a step of drying the membrane composite unit. This step allows the residual liquid on and inside the membrane composite unit to evaporate naturally for later use. The drying temperature can be room temperature, and the drying time can be 12 h to 24 h. This further creates a nearly seamless, bubble-free interface between the membrane unit and the first substrate, which is beneficial for high-fidelity circuit transfer.

[0072] In the example, the average size change rate of the circuit before and after transfer in the above step S20 is less than 0.3%, and it remains basically unchanged. However, the average size change rate before and after transfer in air is generally more than 22%, which fully demonstrates the advantages of this preparation method.

[0073] Step S30 is the second bonding process. This step takes a membrane unit that has not undergone the first bonding process as the first unit, denoted as N1. Since it has not undergone the first bonding process, its first surface (the side where the flexible film is bonded to the circuit) is exposed and not bonded to the first substrate. This first surface is used as the front surface. Then, a membrane composite unit that has undergone the first bonding process is used as the second unit, denoted as N2, with its second surface as the rear surface. The front and rear surfaces are bonded together, that is, the two flexible films are bonded together, and the circuit in the front surface is bonded between these two flexible films. Because the membrane composite unit has the first substrate as a temporary support carrier, the second bonding process can maintain the shape stability of the membrane unit in N2. Optionally, N1 also has a sacrificial layer and a second substrate, which also helps to further maintain the shape stability of the membrane unit in N1. Therefore, the second bonding process helps to improve the flatness, alignment accuracy, and interface bonding quality when the two flexible films are bonded, and helps to reduce circuit distortion and accuracy loss.

[0074] During the second bonding process, N1 can be laid flat, and then N2 can be slowly placed downwards to bond with N1. A certain pressure can be applied, such as applying a pressure of 5 kPa to 20 kPa by placing weights, and maintaining it for about 10 s, in order to improve the interfacial bonding strength between the membrane units in N1 and N2.

[0075] In some embodiments, prior to the second bonding process described above, a step of cutting the film composite unit is included, such that during the second bonding process, the contour of the front side encompasses the contour of the rear side. The cutting process primarily involves cutting N2 to a size slightly smaller than N1, ensuring that the front side completely covers the rear side. This allows a portion of the circuit structure in N1 to be exposed as an interface for connecting to external circuits, or as electrodes for input or output signals, rather than being completely covered by N2, thus affecting the circuit's external connectivity. Furthermore, when the flexible film edge in N2 has undergone the aforementioned fixing process, such as when a PET frame and PI tape are provided, this cutting process can simultaneously remove the frame and PI tape, leaving only the film unit and the first substrate in N2, preventing the introduction of unnecessary components into the multilayer flexible electronic device.

[0076] In some embodiments, during the second bonding process, the edges of the circuit on the front side contain electrodes, and after the second bonding process, the electrodes are exposed. The arrangement of electrodes on the edges of the circuit allows N1 to be directly used as a contact point for external signal input, and the exposed electrodes after the second bonding process facilitate timely input or output of signals to the final multilayer flexible electronic device.

[0077] In the example, the above-described cutting method, or the specific method for exposing the electrodes after the second bonding process, allows for flexible design of the spatial distribution of electrode points based on the object to be detected or contacted by the multilayer flexible electronic device, such as the body surface, muscles, organs, or tissue types. This ensures that the electrodes are as closely attached to and match the anatomical structure and functional areas of the target stimulus or recording object as possible, thereby precisely targeting the target nerve or muscle tissue. This not only enables high spatial resolution and high accuracy neural stimulation but also allows for high-fidelity electrophysiological signal acquisition and monitoring.

[0078] Step S40 is the step of peeling off the first substrate in N2. Since the membrane unit in N1 has been tightly bonded to the membrane unit in N2 after the second bonding process described above, the first substrate has completed its function as a temporary support carrier. Peeling off the first substrate at this point exposes the membrane unit in N2, facilitating subsequent repeated processing.

[0079] Please see Figure 9In some embodiments, the bonding strength between the front and rear surfaces is greater than the bonding strength between the first surface and the surface of the first substrate. This facilitates selective separation during the peeling of the first substrate, peeling only the first substrate in N2 without easily damaging the membrane units, ensuring that the membrane units in N2 remain intact and bonded to the membrane units in N1, thereby guaranteeing the integrity and functional continuity of the multilayer structure. This meets the requirements when the flexible membrane contains SEBS and the first substrate contains PDMS. If the flexible membrane is a PDMS membrane, other membranes can be selected for the first substrate instead of a PDMS membrane to avoid damaging the membrane units during peeling.

[0080] Please see Figure 10 , Figure 11 In some embodiments, the peeling angle of the peeling process is 0° to 80°, and the peeling speed is 0.1 mm / s to 20 mm / s. In exemplary cases, the peeling angle can be any value or a range between any two of 0°, 15°, 30°, 45°, 60°, and 80°. The peeling angle refers to the angle between the direction of the applied peeling force and the plane of the area not yet peeled. Such a controllable peeling angle and peeling speed allows the peeling front of the interface to advance stably along the interface between the two layers, peeling only the first substrate without easily damaging the membrane unit. However, if the peeling parameters are inappropriate, the interfacial stress will be large, potentially causing the two membrane units that have undergone the second bonding process to delaminate.

[0081] Step S50 is the step of repeating the above steps to finally fabricate a multilayer flexible electronic device. After the above steps S10 to S40, a device with two layers of circuitry has been formed, which can be used as a multilayer flexible electronic device. If a device with more layers of circuitry is required, the above steps S30 to S40 can be repeated. Since the first surface of N2 is the same as the front surface of N1 in step S30 after the peeling process in step S40, both being the side where the flexible film is bonded to the conductive layer and exposed, the first surface of N2 can be used as a new front surface. A new film composite unit is then provided, denoted as N3, and the second surface of it can be used as a back surface. The above steps of repeating the second bonding process between the front and back surfaces and peeling off the first substrate can be repeated to continuously laminate and stack, thereby obtaining a multilayer flexible electronic device.

[0082] After this repeated processing, each flexible film simultaneously serves a dual function: on the one hand, it acts as a supporting substrate for the upper circuitry, and on the other hand, it serves as an encapsulation for the lower circuitry. In the example, this can be combined with the electrode exposure method in step S40 above, so that the electrode points are exposed layer by layer in a stepped structure, realizing the construction of a high-density, high-integration, and high-throughput flexible electronic system.

[0083] In some embodiments, the total number of second bonding processes is 1 to 30 times. In exemplary cases, this can include, but is not limited to, any value or a range between any two values ​​of 1, 5, 9, 14, 22, or 30 times. These bonding processes enable the construction of at least two-layer flexible circuits with high integration, volume utilization, and channel count. In an exemplary case, nine second bonding and peeling processes can be performed to ultimately fabricate a ten-layer flexible electronic device with a total time of no more than 3 hours. This significantly reduces manufacturing complexity, equipment dependence, and time costs, making it suitable for high-throughput, low-cost fabrication needs.

[0084] In some embodiments, after the final stripping process is completed, the following step S51 is included:

[0085] S51: Encapsulate the newly formed front surface. This step is performed after the final glass processing. Since the newly formed front surface is the side of the membrane unit where the circuitry is integrated, complete exposure may affect its electrical stability. Encapsulation protects the circuitry. In the example, the material of the encapsulation layer can be the same as the flexible membrane material, and the thickness of the encapsulation layer can be 0.4 μm to 10 μm. The encapsulation method can refer to steps S10 to S20 above, except that the circuitry is not included. Instead, the flexible membrane and the first substrate are directly bonded in a liquid for the first bonding process, followed by a second bonding process and a peeling process to complete the encapsulation.

[0086] In some embodiments, when the membrane unit is bonded to the sacrificial layer on the surface of the second substrate, after the final peeling process is completed, the following step S52 is included:

[0087] In a multilayer flexible electronic device, the sacrificial layer and the second substrate are immersed in a liquid to dissolve the sacrificial layer. This step is taken into account that after the entire multilayer flexible electronic device is fabricated, all film composite units are removed from the liquid, and even if there is a sacrificial layer, it has already dissolved. However, N1 is a film unit that has not undergone the first bonding process. If N1 is still attached to the sacrificial layer on the surface of the second substrate, the sacrificial layer and the second substrate can be immersed in the liquid to dissolve the sacrificial layer and detach the second substrate, thus obtaining the desired multilayer flexible electronic device. Alternatively, the entire multilayer flexible electronic device can be immersed in the liquid, and after the sacrificial layer dissolves, the device can be removed and dried.

[0088] In the example, the flexible film in step S10 is an SEBS film, the sacrificial layer is a PSSNa layer, the second substrate is glass, and the circuit is formed by vapor deposition. The edges of the flexible film in the film unit are fixed with a PET frame and tape. In step S20, the first substrate is a PDMS film, and the liquid is water. After the first bonding treatment is performed in water, the film is removed, dried, and cut. Finally, steps S30 to S40 are repeated to obtain a multilayer flexible electronic device. Using these materials and following these processing methods helps to maintain the structural stability of the film unit during the transfer process, resulting in high circuit fidelity. Furthermore, it allows for the rapid fabrication of devices with multiple layers while maintaining a relatively high yield.

[0089] In the example, the above-mentioned preparation method has a simple technical process and high stability, with an overall yield rate of over 96.2%. In contrast, the flexible film is easily deformed during the existing lamination process, which affects the accuracy and reliability of the circuit and results in a lower yield rate.

[0090] A second aspect of this application provides a multilayer flexible electronic device, which is prepared by the preparation method described in the above-described embodiments of this application.

[0091] The multilayer flexible electronic device in this application has high structural stability and high electrical stability. It can withstand large tensile deformation while the resistance remains within the usable range. Moreover, the conductivity does not significantly decrease after repeated tensile deformation. It has good long-term stability and reliability in dynamic working environments.

[0092] The third aspect of this application provides an application of a multilayer flexible electronic device, wherein the multilayer flexible electronic device prepared by the above-described preparation method of this application is applied to at least one of wearable flexible devices, implantable physiological devices, brain-computer interfaces, flexible electronic packaging, and flexible electronic integration.

[0093] Since the multilayer flexible electronic devices prepared by the above-described embodiments of this application have advantages such as flexible conductivity, ultrathinness, high density, high volume utilization, and multilayer integration, they can be applied in wearable flexible devices, implantable physiological devices, brain-computer interfaces, flexible electronic packaging, flexible electronic integration and other equipment or processes. Furthermore, they have significant advantages and broad application prospects in cutting-edge fields such as advanced medicine, neurorehabilitation, functional reconstruction and intelligent diagnosis and treatment.

[0094] Specifically, multilayer flexible electronic devices can be applied to wearable flexible devices. In applications involving surface nerve stimulation and physiological signal acquisition, devices need to integrate high-density electrodes within a limited area while maintaining good flexibility and skin adhesion. The multilayer flexible electronic device fabricated by the method described in this application can achieve high-density construction of multilayer flexible electrodes, significantly improving electrode duty cycle and volume utilization while enhancing the device's stable performance under bending and stretching conditions. It is suitable for applications such as surface nerve stimulation, electromyography (EMG), and electroencephalography (EEG) signal acquisition.

[0095] Wearable flexible devices can also be high-density wearable medical electronic systems. In the fields of continuous health monitoring and disease-aided diagnosis, wearable medical electronic systems typically need to integrate multiple functions such as signal acquisition, stimulation, data processing, and transmission. The multilayer flexible electronic device prepared by the method in this application can achieve multifunctional integration without significantly increasing the device size, improving system integration and wearing comfort, and is suitable for long-term monitoring of electrocardiogram, electromyography, and other physiological parameters.

[0096] Multilayer flexible electronic devices can be applied to implantable physiological devices and brain-computer interfaces. In these applications, devices have stringent requirements for high channel count, small size, and long-term reliability. The multilayer flexible electronic devices fabricated by the method described in this application can achieve three-dimensional integration of functional units within an extremely small volume, and ensure structural stability through reliable interlayer bonding, making them suitable for long-term implantation applications in complex biological interfaces such as the spinal cord, peripheral nerves, and brain tissue.

[0097] Multilayer flexible electronic devices can be applied to flexible electronic packaging and integration. As flexible electronic systems evolve towards higher channel counts and higher integration levels, traditional planar manufacturing and packaging methods struggle to integrate complex functions within a limited area. The multilayer flexible electronic devices fabricated using the methods described in this application can achieve vertical integration and reliable packaging of multilayer functional units without significantly increasing device volume. This makes them suitable for constructing high-density flexible sensor arrays, stimulus arrays, and system-level flexible electronic modules, contributing to improved integration, reliability, and long-term stability of flexible electronic systems.

[0098] The following description is based on specific embodiments.

[0099] Example 1

[0100] Please see Figure 14 This embodiment provides a multilayer flexible circuit and its fabrication method, including the following steps S1 to S4:

[0101] S1: Prepare membrane units.

[0102] After the glass substrate (second substrate) was activated by plasma, a sodium polystyrene sulfonate (PSSNa) solution with a concentration of 80 mg / mL was spin-coated at a spin-coating speed of 1500 rpm, and then annealed at 150 °C for 60 s to obtain a water-soluble sacrificial layer.

[0103] A 100 mg / mL SEBS toluene solution was spin-coated onto the surface of the sacrificial layer away from the glass substrate at a spin-coating speed of 1500 rpm. After curing at 150 °C for 10 min, a SEBS film (flexible film) with a thickness of 3 μm was formed.

[0104] A gold functionalized pattern (circuit) of approximately 100 nm thickness was thermally deposited on the surface of the SEBS thin film away from the sacrificial layer using a mask at a rate of 0.03 nm / s. An electrode array was formed at the edges of the circuit, as shown below. Figure 4 As shown.

[0105] The flexible membrane and the circuit form a membrane unit, and the membrane unit is disposed on a sacrificial layer bonded to a glass substrate.

[0106] S2: First bonding process.

[0107] like Figure 2 As shown, a polyethylene terephthalate (PET) frame is set around the SEBS film in the membrane unit and fixed with polyimide (PI) tape. The membrane unit is then placed in deionized water (liquid) to dissolve the PSSNa sacrificial layer, allowing the membrane unit to detach from the glass substrate and float in the water.

[0108] In addition, a PDMS thick film (first substrate) was prepared by mixing PDMS base liquid and curing agent at a mass ratio of 10:1 and stirring. The mixture was then spin-coated onto another spare glass substrate at a speed of 1000 rpm and cured at 110°C for 6 min. The film was then peeled off from the glass substrate to obtain a self-supporting PDMS thick film with a certain strength and a thickness of 400 μm.

[0109] Next, the membrane unit is transferred to the pre-prepared PDMS thick membrane in an aqueous environment. Specifically, both the membrane unit and the PDMS thick membrane are immersed in deionized water. The side of the membrane unit with the circuit is first bonded to the side of the PDMS thick membrane, and appropriate pressure is applied to bond them together, so that the membrane unit is transferred to the PDMS thick membrane.

[0110] After the transfer is completed, the whole thing is lifted out of the water and dried at room temperature for 16 hours to obtain the membrane composite unit. The PDMS thick membrane in the unit can be used as a temporary support carrier for the membrane unit.

[0111] S3: Second bonding and peeling process.

[0112] Another membrane unit is prepared according to the method in step S1 and bonded to the sacrificial layer. This membrane unit is denoted as N1 and does not undergo the first bonding process in step S2.

[0113] The membrane composite unit in step S2 is cut off by removing the PET frame and PI tape at the edges, so that its outline is smaller than the outline of N1 and can be included by the outline of N1. The electrodes at both ends of the circuit in N1 can be exposed. The membrane composite unit cut according to these requirements is denoted as N2.

[0114] Place N1 flat, with the side of N1 containing the circuit as the front side, and that side facing upwards; and the side of N2 that originally contained the sacrificial layer (that is, the side facing away from the circuit) as the back side. Perform a second bonding process on the front and back sides. Specifically, slowly place N2 downwards to allow the back side to adhere to the front side, then place a weight and hold for 10 seconds. Apply a pressure of about 10 kPa to the bonded film to cause the SEBS to bond with each other, thereby allowing N1 and N2 to be tightly bonded.

[0115] The first substrate in N2 after the second bonding process is peeled off at an angle of about 20° and a speed of about 10 mm / s. The first substrate is gradually peeled off.

[0116] S4: Constructing multilayer devices and post-processing.

[0117] like Figure 3 , Figure 4 As shown, in step S3, the side of the membrane unit in N2 that was peeled off from the first substrate and had the circuit attached forms a new front side. Therefore, steps S2 to S3 are continued, and the new membrane unit is continuously attached to the already constructed membrane unit through a first bonding process, a second bonding process, and a peeling process. The second bonding process is performed a total of 9 times, resulting in a final device with 10 layers of circuitry, as shown... Figure 4 As shown.

[0118] After the final stripping process, a layer of SEBS film is applied to the surface of the last membrane unit to prevent the entire circuit from being completely exposed. This SEBS film can be transferred using the methods described in steps S1 to S3 above, except that no circuitry is incorporated into it.

[0119] After packaging, the entire device is immersed in deionized water, especially the glass substrate and sacrificial layer. Specifically, the sacrificial layer still bonded to N1 and the glass substrate on the other side of the sacrificial layer are immersed in deionized water. The sacrificial layer dissolves in the deionized water, the glass substrate separates from the constructed device, and finally it is dried to obtain a multilayer flexible electronic device.

[0120] Example 2

[0121] This embodiment provides a multilayer flexible circuit and its fabrication method. The only difference from Embodiment 1 is that the liquid in step S2 is changed from deionized water to tap water. Everything else is the same.

[0122] Example 3

[0123] This embodiment provides a multilayer flexible circuit and its fabrication method. The only difference from Embodiment 1 is that the liquid in step S2 is changed from deionized water to ethanol. Everything else is the same.

[0124] Example 4

[0125] This embodiment provides a multilayer flexible circuit and its fabrication method. The only difference from Embodiment 1 is that the SEBS film in step S1 and the SEBS film for encapsulation in step S4 are replaced with PDMS films, and the first substrate in steps S2 to S5 is replaced with a polyethylene terephthalate thick film. All other aspects are the same.

[0126] Example 5

[0127] This embodiment provides a multilayer flexible circuit and its fabrication method. The only difference from Embodiment 1 is that the PDMS thick film in step S2 is replaced with a polytetrafluoroethylene thick film. Everything else is the same.

[0128] Example 6

[0129] This embodiment provides a multilayer flexible circuit and its fabrication method. The only difference from Embodiment 1 is that the thickness of the SEBS film in step S1 and the SEBS film for encapsulation in step S4 is changed from 3 μm to 1 μm. All other aspects are the same.

[0130] Example 7

[0131] This embodiment provides a multilayer flexible circuit and its fabrication method. The only difference from Embodiment 1 is that the second bonding process in step S4 is performed 14 times, resulting in a final device with 15 circuit layers. Everything else is the same.

[0132] Example 8

[0133] This embodiment provides a multilayer flexible circuit and its fabrication method, which differs from Embodiment 1 only in that: Figure 11 As shown, the peeling angle in step S3 is approximately 90°. Everything else is the same.

[0134] Comparative Example 1

[0135] This comparative example provides a multilayer flexible circuit and its fabrication method, which differs from Example 1 in that: Figure 1As shown in a, the SEBS film in step S1 and the SEBS film used for encapsulation in step S4 are both replaced with parylene film, which is a plastic film. Furthermore, the circuit is not deposited by vapor deposition in step S1, and the plastic film is directly peeled off in air instead of being transferred in deionized water in step S2. Subsequently, a traditional lamination method is used, first setting the circuit on the plastic film to form a unit, and then fabricating a multilayer device by sequential lamination.

[0136] Comparative Example 2

[0137] This comparative example provides a multilayer flexible circuit and its fabrication method, which differs from Example 1 in that: Figure 1 As shown in b, in step S2, no PET frame is set around the SEBS film, nor is PI tape used for fixation. Furthermore, the circuit is not deposited in step S1. In step S2, after dissolving the sacrificial layer in deionized water, the SEBS film is removed from the water. Subsequently, a traditional lamination method is used, first setting the circuit on the SEBS film to form a unit, and then fabricating a multilayer device through sequential lamination.

[0138] Comparative Example 3

[0139] This comparative example provides a multilayer flexible circuit and its fabrication method. The only difference from Example 1 is that the first bonding process in step S2 is not performed in water, but directly bonded to the PDMS thick film in air. All other aspects are the same.

[0140] The differences between the cases are shown in Table 1. The yield rate in Table 1 refers to the fact that, on the basis of good structure, the circuit accuracy between layers can also meet the expectations. Only then is it recorded as a good product. The yield rate is calculated according to the batch production of devices for each scheme.

[0141] Table 1

[0142]

[0143] Related performance tests

[0144] 1. Relevant tests on the number and size of bubbles

[0145] Using an electron optical microscope and following the method of taking optical micrographs, the number of bubbles generated during each film transfer in step S2 of each case was statistically analyzed, and the interface bubble situation in a 10 mm × 10 mm area was recorded.

[0146] 2. Interface separation energy

[0147] Using a universal testing machine, the front and back surfaces in each case were bonded together and then separated. By calculating the integral of the force and displacement during the separation process, the separation energy between the front and back surfaces in each case was obtained. The separation energy between the membrane unit and the first substrate was then obtained using this method. The test results in Example 1 are as follows... Figure 9 As shown, the bonding strength between SEBS is higher than that between SEBS and PDMS, which minimizes the impact on the SEBS film when peeling off the PDMS thick film.

[0148] 3. Impedance and phase angle testing after long-term cycling

[0149] The multilayer flexible electronic devices fabricated in each case were subjected to 1000 stretching cycles, with a stretching deformation rate of 30% per cycle. The impedance and phase angle of the devices were measured using an electrochemical workstation following a three-electrode system measurement method. The test results in Example 1 are as follows: Figure 12 As shown.

[0150] Analysis of results for each case

[0151] Each embodiment constructs a multilayer flexible electronic device by repeating the first bonding process, the second bonding process, and the peeling process. The device exhibits ideal performance and high yield.

[0152] The test results of Examples 1 to 3 are similar, indicating that the method of transferring SEBS film to PDMS thick film surface in liquids such as deionized water, tap water, and ethanol produces fewer bubbles, the SEBS film is not easily deformed, the circuit size change rate before and after transfer is extremely low, the fidelity is high, the final device structure yield is also the highest, and the impact on the circuit and the overall device structure is low.

[0153] The multilayer flexible electronic device prepared in Example 1 can be used as a ten-layer flexible neuromodulation electrode, such as... Figure 13 As shown in figure a, it has been successfully implanted into the T13–L1 segment of the rat spinal cord. This flexible electrode exhibits excellent deformation compliance, achieving 360° circumferential coverage along the spinal cord periphery after implantation and closely adhering to the spinal cord surface. Simultaneously, the electrode integrates a high density of electrode sites, enabling precise and controllable electrical stimulation of different functional areas of the spinal cord at various spatial locations. Figure 13 As shown in b, by selectively activating different electrode sites, anesthetized rats can be induced to produce a variety of highly selective movements, including independent forward and backward movements of the left and right hind limbs.

[0154] Examples 4 and 5 replaced SEBS and PDMS with other materials with similar functions, and the final results were also quite satisfactory, further demonstrating that the first bonding treatment, the second bonding treatment, and the peeling treatment are generally applicable to this type of material. Relatively speaking, the results of using SEBS film as the flexible film and PDMS thick film as the first substrate are the best, representing the optimal solution. The results of Examples 4 and 5 are slightly lower, but still quite close to those of Example 1.

[0155] Example 6 further reduced the SEBS film thickness to 1 μm, which is already an extremely thin scale, increasing the difficulty even further. However, the rate of change in circuit dimensions before and after transfer, as well as the yield of the fabricated device, remained at a high level. Example 7 further fabricated a multilayer flexible electronic device with 15 layers. The more layers, the more difficult the fabrication becomes, but the relevant performance in this case was also maintained at a high level. It can be seen that the fabrication method of this application is applicable to the fabrication of multilayer flexible electronic devices with ultrathin flexible films of various thicknesses, and can fabricate high-layer devices while maintaining high performance and yield.

[0156] In Example 8, the transfer was also performed in deionized water, resulting in a low rate of change in circuit dimensions before and after the transfer. However, because the peeling angle for PDMS during subsequent device fabrication reached approximately 90°, the excessively large peeling angle made it easy to lift the membrane unit during PDMS peeling, affecting the final yield.

[0157] like Figure 1 As shown in a, in Comparative Example 1, a plastic film such as parylene was used instead, but instead of performing the first bonding process in the liquid, it was directly peeled off from the sacrificial layer on the glass surface in the air. The plastic film would break directly, making it impossible to further fabricate the device, which corresponds to the problem of ultrathin plastic films mentioned in the background art.

[0158] like Figure 1 As shown in b, in Comparative Example 2, the flexible membrane edges were not fixed with a frame. After the sacrificial layer dissolved, the SEBS film collapsed. Furthermore, no initial bonding process was performed in the liquid; instead, it was directly removed from the water. Figure 1 As can be seen in the last figure (iii) of b in the text, the SEBS film in the air has further collapsed and curled into a bundle, making it impossible to further fabricate devices, which corresponds to the problem of ultrathin flexible films mentioned in the background art.

[0159] like Figure 6 , Figure 7 , Figure 8As shown, in Comparative Example 3, the first bonding process is not performed in water, but in air. This results in a large number of large bubbles between the SEBS film and the PDMS thick film, which affects the shape of the SEBS film and consequently the shape of the circuit. This leads to a large change in circuit size before and after the transfer, a significant decrease in fidelity, and ultimately a low yield of the device.

[0160] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for fabricating a multilayer flexible electronic device, characterized in that, Includes the following steps: A membrane unit is provided, including a flexible membrane and a circuit bonded to a surface of the flexible membrane, wherein the surface of the membrane unit in which the circuit is bonded is referred to as a first surface and the surface opposite to the first surface is referred to as a second surface; The membrane unit and the first substrate are immersed in a liquid, the first surface and the surface of the first substrate are subjected to a first bonding treatment, and then the membrane composite unit is removed from the liquid. Using the first surface of the membrane unit that has not undergone the first bonding process as the front surface and the second surface of the membrane composite unit as the rear surface, the front surface and the rear surface are subjected to a second bonding process. The first substrate in the membrane composite unit after the second bonding process is peeled off, so that the first surface in the membrane composite unit forms a new front surface; Repeat the second bonding process and the peeling process to obtain a multilayer flexible electronic device.

2. The preparation method according to claim 1, characterized in that: The flexible membrane contains an elastic material, which includes at least one of styrene-ethylene-butene-styrene block copolymer, polyurethane, polydimethylsiloxane, and polyurethane acrylate; and / or The first substrate contains at least one of polydimethylsiloxane, polyethylene terephthalate, and polytetrafluoroethylene; and / or, The total number of times the second bonding process is 1 to 30.

3. The preparation method according to claim 1 or 2, characterized in that: The liquid includes at least one of water, ethanol, methanol, and isopropanol; and / or, The thickness of the flexible membrane is 0.4 μm to 10 μm; and / or, The thickness of the circuit is 10 nm to 300 nm; and / or, The thickness of the first substrate is 100 μm to 600 μm.

4. The preparation method according to claim 1 or 2, characterized in that: After removing the membrane composite unit from the liquid, the process further includes a step of drying the membrane composite unit; and / or, The bonding strength between the front surface and the rear surface is greater than the bonding strength between the first surface and the surface of the first substrate; and / or, The peeling angle of the peeling process is 0° to 80°, and the peeling speed is 0.1 mm / s to 20 mm / s.

5. The preparation method according to claim 1 or 2, characterized in that, The method for preparing the flexible membrane includes the following steps: A first film-forming treatment is performed on one side of the second substrate to form a sacrificial layer; A second film-forming process is performed on the surface of the sacrificial layer opposite to the second substrate to form the flexible film; The sacrificial layer can be dissolved in the liquid.

6. The preparation method according to claim 5, characterized in that: The second substrate comprises at least one of glass, silicon wafer, sapphire, and polyethylene terephthalate; and / or, The sacrificial layer contains at least one of sodium polystyrene sulfonate, polyvinyl alcohol, and polyvinylpyrrolidone.

7. The preparation method according to claim 5, characterized in that, Immersing the membrane unit in the liquid includes the following steps: First, the edge of the flexible membrane in the membrane unit is fixed. Then, the membrane unit is immersed in the liquid, so that the sacrificial layer dissolves in the liquid, resulting in the membrane unit with the edge fixed. And / or, After the final stripping process is completed, the following steps are included: The newly formed front surface is then encapsulated. And / or, After the final stripping process is completed, the following steps are included: The sacrificial layer and the second substrate in the multilayer flexible electronic device are immersed in the liquid to dissolve the sacrificial layer.

8. The preparation method according to any one of claims 1, 2, 6, and 7, characterized in that: Before performing the second bonding process, the method further includes a step of cutting the film composite unit so that, during the second bonding process, the contour of the front side encompasses the contour of the rear side; and / or, During the second bonding process, the edge of the circuit on the front side contains electrodes, and after the second bonding process, the electrodes are exposed.

9. A multilayer flexible electronic device, characterized in that: It is prepared by a method comprising any one of claims 1 to 8.

10. An application of a multilayer flexible electronic device, characterized in that: The multilayer flexible electronic device prepared by any one of the preparation methods described in claims 1 to 8 is applied to at least one of wearable flexible devices, implantable physiological devices, brain-computer interfaces, flexible electronic packaging, and flexible electronic integration.

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