Double-sided flexible neural electrode and preparation method thereof

Abstract

The invention relates to a double-sided flexible neural electrode and a preparation method thereof, and the preparation method comprises the steps: preparing a first polymer insulating layer with a pit on a sacrificial layer, and then forming a metal electrode point and a wire for filling the pit; covering a second polymer insulation packaging layer, etching a patterned opening in a region corresponding to an electrode point on the second polymer insulation packaging layer, enabling the upper surface of the electrode point to be partially exposed through the design, and enabling the packaging layer material which is not etched to serve as a supporting structure to be in close contact with the surface of the electrode point to form mechanical anchoring; and removing the sacrificial layer to completely expose the lower surface of the electrode point, thereby forming a unique double-sided contact interface. Compared with the prior art, the device has the advantages that the upper surface and the lower surface of the electrode point are exposed at the same time for bidirectional electrophysiological recording / stimulation, the structural stability of the electrode point is enhanced through the unique mechanical anchoring design, and therefore the long-term reliability of the device in the biological environment is guaranteed while the signal collecting capacity is improved.

Description

Technical Field

[0001] This invention relates to the field of biomedical engineering technology, and in particular to a bifacial flexible neural electrode and its preparation method. Background Technology

[0002] Neural electrodes are crucial tools in basic neuroscience research and clinical applications such as brain-computer interfaces, used to record neural electrical signals or electrically stimulate neural tissue. Compared to traditional rigid electrodes, flexible neural electrodes, due to their modulus being more compatible with brain tissue, can effectively reduce foreign body reactions during chronic implantation and improve the stability of long-term recording.

[0003] Currently, most widely researched and applied flexible neural electrodes are single-sided structures, meaning that only one surface of the electrode point is exposed to the external environment and in contact with nerve tissue for signal acquisition or stimulation. However, this single-sided design has inherent limitations when applied to three-dimensional structures such as the cerebral cortex: firstly, it can only sense neural activity on one side of the electrode and cannot capture electrophysiological signals from the other side, resulting in incomplete information acquisition; secondly, the effective range of its electric field is mainly limited to one side of the electrode, restricting the spatial range and efficiency of electrical stimulation.

[0004] To overcome the limitations of single-sided electrodes, the academic community has begun exploring bifacial flexible electrode structures, aiming to enable both the upper and lower surfaces of the electrode to serve as functional interfaces, thereby achieving synchronous interaction of electrical activity on both sides of nerve tissue. However, existing bifacial electrode fabrication techniques are typically complex. For example, they require independent micro- and nano-fabrication on both sides of a flexible substrate to define the upper and lower electrodes, and the introduction of an additional polymer insulating layer between the two layers to achieve electrical isolation between the upper and lower conductors. This approach has significant drawbacks: firstly, the complex bifacial alignment process increases the fabrication difficulty and cost; secondly, the introduction of the intermediate insulating layer inevitably increases the overall thickness of the electrode, reducing its flexibility and adhesion to nerve tissue, partially offsetting the advantages of flexible electrodes.

[0005] Existing technology CN115399777A proposes a flexible bidirectional neural probe, which aims to improve electrode density and omnidirectional acquisition capability by distributing electrode points on both sides of a polyimide substrate. However, the fabrication process of this technology relies on complex microfabrication steps, such as patterning with aluminum hard masks or lamination techniques, requiring multiple exposures and flipping for attachment, resulting in a cumbersome process and low yield. The introduction of an intermediate insulating layer also increases the electrode thickness and reduces flexibility. Another existing technology CN116746935A develops a flexible neural electrode with a multilayer bidirectional signal transmission structure, which increases the number of channels through three-dimensional stacking of signal transmission layers. However, the stacking of multiple insulating and metal layers significantly increases the electrode thickness, sacrificing the thin-layer advantage of flexible electrodes and potentially increasing the risk of implantation damage.

[0006] Therefore, there is an urgent need in this field for a novel double-sided flexible neural electrode with simple process and compact structure and its preparation method, in order to solve the problems of single information acquisition dimension, complex process and flexibility in the existing technology. Summary of the Invention

[0007] The purpose of this invention is to overcome the defects of the prior art by providing a double-sided flexible neural electrode and its preparation method. This not only enables simultaneous exposure of the upper and lower surfaces of the electrode for bidirectional electrophysiological recording / stimulation, but also enhances the structural stability of the electrode through a unique mechanical anchoring design. This improves signal acquisition capabilities while ensuring the long-term reliability of the device in a biological environment.

[0008] The objective of this invention can be achieved through the following technical solutions: The first aspect of this invention provides a bifacial flexible neural electrode, comprising: A flexible polymer matrix, wherein the flexible polymer matrix is ​​composed of a first polymer insulating layer and a second polymer insulating encapsulation layer; A metal patterned layer is embedded in the flexible polymer matrix, the metal patterned layer including wires and electrode points electrically connected to the wires; The electrode point has a double-sided exposed structure, with its lower surface coplanar with the lower surface of the first polymer insulating encapsulation layer to form a first biological contact interface, and its upper surface exposed through a patterned opening on the second polymer insulating encapsulation layer to form a second biological contact interface. Furthermore, the second polymer insulating encapsulation layer forms a support structure above the electrode point, the support structure being in contact with the upper surface of the electrode point for mechanical anchoring of the electrode point.

[0009] Furthermore, the patterned opening portion can take the form of one or more of the following: a regular grid, an array of circular holes, or a honeycomb pattern.

[0010] Furthermore, the patterned openings allow the exposed area of ​​the upper surface of the electrode point to account for 20% to 90% of the total area of ​​the upper surface of the electrode point.

[0011] Furthermore, the electrode points are used to synchronously record or stimulate neural electrical activity from their upper and lower sides.

[0012] Furthermore, the first polymer insulating layer forms a pit structure below the electrode point that complements the undulating shape of the electrode point. The recessed structure and the patterned openings on the second polymer insulating encapsulation layer are complementary in spatial distribution, together forming a three-dimensional mechanical anchoring structure for the electrode points to avoid any suspended areas at the electrode points.

[0013] A second aspect of the present invention provides a method for preparing the above-described bilateral flexible neural electrode, comprising the following steps: S1, Provide a sacrificial layer; S2. A first polymer insulating layer is formed on the sacrificial layer; S3. Etch at least one pit into the first polymer insulating layer; S4. A metal pattern layer is prepared on a first polymer insulating layer with the etched pits, the metal pattern layer including wires and electrode points electrically connected to the wires, wherein the electrode points fill the pits; S5. A second polymer insulating encapsulation layer is formed on the metal pattern layer; S6. On the second polymer insulating encapsulation layer, a patterned opening is formed in the region corresponding to the electrode point. The second polymer insulating encapsulation layer in the patterned region of the opening is removed by an etching process, thereby partially exposing the upper surface of the electrode point. At the same time, the unetched second polymer insulating encapsulation layer serves as a support structure and contacts the surface of the electrode point below for mechanical anchoring of the electrode point. S7. Remove the sacrificial layer to release the flexible electrode structure, thereby exposing the lower surface of the electrode point to form a double-sided electrode structure.

[0014] Furthermore, after S7, the following process is also included: simultaneously modifying the upper and lower surfaces exposed at the electrode points with low-resistivity material layers by electrochemical deposition.

[0015] Furthermore, the low-resistivity material layer is a conductive polymer selected from PEDOT:PSS, platinum black, titanium nitride, and iridium oxide.

[0016] Furthermore, in S3, the pits are etched into the first polymer insulating layer using a reactive ion etching process; In S6, the pattern with openings is etched on the second polymer insulating encapsulation layer using a reactive ion etching process.

[0017] Furthermore, the materials of the first polymer insulating layer and the second polymer insulating encapsulation layer are selected from one of polyimide, parylene, benzocyclobutene, and SU-8 photoresist.

[0018] The key to this invention lies in the following: After preparing a first polymer insulating layer with pits on a sacrificial layer, metal electrode points and wires filling the pits are formed; subsequently, a second polymer insulating encapsulation layer is applied, and patterned openings are etched in the corresponding areas of the electrode points on this layer. This design partially exposes the upper surface of the electrode points, while the unetched encapsulation layer material acts as a support structure, making close contact with the electrode point surface to form a mechanical anchor, effectively preventing the electrodes from detaching due to interface stress during implantation and use; finally, the sacrificial layer is removed, completely exposing the lower surface of the electrode points, thus forming a unique double-sided contact interface. The double-sided flexible neural electrode prepared based on this method can simultaneously achieve high spatial resolution recording or precise stimulation of electrical signals on both sides of neural tissue (such as the cerebral cortex) at a single electrode point, significantly improving the signal-to-noise ratio and stimulation localization accuracy, overcoming the limitations of traditional single-sided electrodes in acquiring limited information in a three-dimensional neural environment. Compared with the prior art, the present invention has the following beneficial effects: 1) Two-way interactive capability: A single electrode point allows for simultaneous exposure of the upper and lower surfaces, enabling synchronous recording or stimulation of neural electrical activity from both sides of the electrode. This provides an unprecedented dimension for analyzing the spatial origin of neural signals, and the amount of information acquired significantly exceeds that of traditional single-sided electrodes.

[0019] 2) Excellent mechanical stability: By designing patterned openings and retaining support structures in the upper encapsulation layer, effective mechanical anchoring is achieved for the electrode points. This "embedded" fixation method greatly enhances the bonding strength between the electrode points and the flexible substrate, effectively resists interfacial shear stress during implantation and use, prevents electrode point detachment, and significantly improves the long-term reliability of the device.

[0020] 3) Low impedance and high signal-to-noise ratio: The double-sided exposed structure doubles the effective surface area of ​​electrochemical modification, which can significantly reduce the impedance of the electrode-tissue interface, thus improving the signal-to-noise ratio of the recorded signal and the injection efficiency of the stimulation current.

[0021] 4) Process compatibility and scalability: This method is based on mature microfabrication technology, and only adds a patterning etching step for the upper packaging layer to the standard process. The process is simple, highly controllable, and easy to realize the fabrication of arrayed, high-density electrodes. Attached Figure Description

[0022] Figure 1 This is a partial three-dimensional structural diagram of the double-sided flexible neural electrode in an embodiment of the present invention, showing the structure in which the lower surface of the electrode point is fully exposed and the upper surface is partially exposed and anchored through a mesh-like opening.

[0023] Figure 2 This is a schematic cross-sectional view of the process flow of the preparation method of the present invention.

[0024] Figure 3These are optical microscope images, among which... Figure 3 a is an optical microscope photograph of the second polymer insulating layer after a grid pattern has been created; Figure 3 b is an optical microscope image of the surface of the underlying electrode points exposed after the sacrificial layer has been released.

[0025] Figure 4 These are optical microscope images of the upper and lower surfaces of the double-sided electrode points after platinum black modification in an embodiment of the present invention.

[0026] Figure 5 The impedance of the double-sided electrode points after platinum black modification in this embodiment of the invention is shown to be lower than that of a single-sided electrode of the same size.

[0027] Figure 6 This is a schematic diagram of a double-sided flexible neural electrode with a complementary polymer insulating layer structure in an embodiment of the present invention.

[0028] Figure 7 This is a process flow diagram of the preparation method of the present invention. Detailed Implementation

[0029] The basic concept of this invention lies in fabricating a double-sided flexible neural electrode with exposed upper and lower surfaces of the electrode points through an ingenious micro-nano fabrication process. The core fabrication steps include: sequentially fabricating a first polymer insulating layer on a sacrificial layer and etching pits; forming metal electrode points and wires filling the pits; covering with a second polymer insulating encapsulation layer and etching patterned openings to partially expose and anchor the upper surface of the electrode points; and finally removing the sacrificial layer to fully expose the lower surface of the electrode points. The patterned openings not only serve for electrical contact, but their unetched portions also critically function as a support structure, mechanically anchoring the electrode points and preventing them from detaching due to stress in the implanted microenvironment. To further improve performance, a low-resistivity material layer can be applied to the exposed double-sided electrode points. The following two embodiments provide a detailed description.

[0030] The electrodes in this invention not only achieve simultaneous exposure of the upper and lower surfaces of the electrode points for bidirectional electrophysiological recording / stimulation, but also enhance the structural stability of the electrode points through a unique mechanical anchoring design. This improves signal acquisition capabilities while ensuring the long-term reliability of the device in a biological environment. To achieve the above objectives, this invention adopts the following technical solution: In specific implementation, a method for preparing a double-sided flexible neural electrode includes the following steps: S1. Provide a sacrifice layer; S2. A first polymer insulating layer is formed on the sacrificial layer; S3. At least one pit is defined and formed on the first polymer insulating layer by photolithography and etching processes; S4. A metal pattern layer is prepared on a first polymer insulating layer with the etched pits, the metal pattern layer including wires and electrode points electrically connected to the wires, wherein the electrode points fill the pits; S5. A second polymer insulating encapsulation layer is formed on the metal pattern layer and the electrode points; S6. On the second polymer insulating encapsulation layer, a patterned opening is formed in the area corresponding to the electrode point by photolithography and etching processes, and the second polymer insulating encapsulation layer in that area is removed, so that the upper surface of the electrode point is partially exposed, while the unetched second polymer insulating encapsulation layer serves as a support structure and contacts the surface of the electrode point to form a mechanical anchor. S7. Remove the sacrificial layer to release the flexible electrode structure, thereby exposing the lower surface of the electrode points to form a double-sided exposed electrode structure.

[0031] In a specific implementation, preferably, after step S7, step S8 is also included: by electrochemical deposition, a low-resistivity material layer, such as conductive polymer PEDOT:PSS, platinum black, titanium nitride, or iridium oxide, is simultaneously modified on the upper and lower surfaces exposed at the electrode point.

[0032] In specific implementation, the pit formed in step S3 can also be a patterned structure, and the pattern and the patterned opening formed on the second polymer insulating encapsulation layer in step S6 can be designed to complement each other in spatial distribution, so as to jointly form a three-dimensional mechanical anchoring of the electrode point from the upper and lower sides, maximize the avoidance of suspended areas, and enhance structural stability.

[0033] In specific implementation, the patterned openings can be designed in various forms such as regular grid, circular hole array or honeycomb, and the opening ratio is configured so that the exposed area of ​​the upper surface of the electrode point accounts for 20% to 90% of the total surface area, so as to achieve the best balance between ensuring the effective charge injection / collection area and mechanical anchoring strength.

[0034] In a specific implementation, the present invention also provides a bifacial flexible neural electrode prepared by the above method. Its structure includes: The flexible polymer matrix is ​​composed of a first polymer insulating layer and a second polymer insulating encapsulation layer; A metal patterned layer embedded in the flexible polymer matrix includes wires and electrode points; The electrode point has a double-sided exposed structure: its lower surface is coplanar with the lower surface of the second polymer insulating encapsulation layer, forming a first biological contact interface; its upper surface is partially exposed through patterned openings on the second polymer insulating encapsulation layer, forming a second biological contact interface. The second polymer insulating encapsulation layer forms a support structure above the electrode point, which contacts the upper surface of the electrode point and provides mechanical anchoring, effectively preventing the electrode point from falling off under stress.

[0035] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Although the description of the present invention is presented in conjunction with preferred embodiments, this does not mean that the features of the invention are limited to these embodiments. On the contrary, the purpose of describing the invention in conjunction with embodiments is to cover other options or modifications that may be derived based on the claims of the present invention. To provide a thorough understanding of the invention, many specific details will be included in the following description. The invention may also be implemented without using these details. Furthermore, to avoid confusion or obscuring the focus of the invention, some specific details will be omitted in the description.

[0036] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0037] Furthermore, the terms "upper," "lower," "left," "right," "top," "bottom," "horizontal," and "vertical" used in the following description should be understood as the orientations shown in the relevant paragraphs and accompanying drawings. These relative terms are for illustrative purposes only and do not imply that the described apparatus must be manufactured or operated in a specific orientation, and therefore should not be construed as limiting the invention.

[0038] It is understood that although terms such as "first," "second," and "third" may be used herein to describe various components, regions, layers, and / or parts, these components, regions, layers, and / or parts should not be limited by these terms, and these terms are only used to distinguish different components, regions, layers, and / or parts. Therefore, the first components, regions, layers, and / or parts discussed below may be referred to as second components, regions, layers, and / or parts without departing from some embodiments of the present invention.

[0039] The implementation process of the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and through multiple embodiments in a non-limiting manner. Those skilled in the art should understand that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the scope of protection of the present invention.

[0040] Any preparation methods, materials, structures, or composition ratios not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0041] Example 1: Fabrication of standard bifacial flexible neural electrodes This embodiment provides a method for fabricating a standard bifacial flexible neural electrode. The lower surface of the electrode is formed by etching simple pits into the sacrificial layer, while the upper surface is partially exposed and anchored through a mesh-like opening. This electrode is suitable for most scenarios requiring low impedance and high signal-to-noise ratio neural signal recording.

[0042] The process flow of this embodiment can be referred to the appendix. Figure 2 and Figure 7 As shown.

[0043] S1: Provides a sacrifice layer (corresponding to) Figure 2 a): The silicon wafer was cleaned using standard RCA and dried with nitrogen. It was then placed in the vacuum chamber of a magnetron sputtering instrument, where a 200 nm thick aluminum film was deposited on the silicon wafer surface at room temperature as a sacrificial layer for subsequent processes.

[0044] S2: Forming the first polymer insulating layer (corresponding to...) Figure 2 b): A polyimide PI-2610 precursor solution was spin-coated onto the aluminum sacrificial layer using a spin coater. The spin coater program was set as follows: first, spin at 500 rpm for 10 seconds to spread the adhesive, then spin at 3000 rpm for 30 seconds to control the thickness. Subsequently, the silicon wafer was placed on a hot plate for stepped soft baking: held at 110°C for 2 minutes, then at 180°C for 5 minutes to remove most of the solvent. Finally, the silicon wafer was placed in a nitrogen-protected tube furnace, heated to 300°C at a rate of 5°C / min, and cured for 1 hour. After natural cooling, a first polymer insulating layer with a smooth surface and a thickness of approximately 2 ± 0.2 μm was obtained.

[0045] S3: Define and etch pits (corresponding to...) Figure 2 c): Positive photoresist was spin-coated onto the surface of the first PI layer. Exposure and development were performed using a photomask (designed with a circular array pattern of 30 μm diameter) to transfer the pattern onto the photoresist. The sample was then placed in the RIE reaction chamber. The etching gas was a mixture of oxygen (O2) and carbon tetrafluoride (CF4) at a flow rate ratio of O2:CF4 = 40 sccm:10 sccm, with a chamber pressure of 50 mTorr and an RF power of 100 W. Under these conditions, the PI etching rate was approximately 100 nm / min. Crucially, the etching time in this step needed to be precisely controlled (approximately 30 minutes) to ensure complete etching through the first PI layer until the surface of the underlying aluminum sacrificial layer was fully exposed. After etching, acetone and isopropanol were used to remove residual photoresist, ultimately forming a through-type circular pit array approximately 3 μm deep and 30 μm in diameter on the first PI layer.

[0046] S4: Fabrication of the metal pattern layer (corresponding to...) Figure 2 d): Metal patterns were fabricated using a lift-off process. First, photoresist was spin-coated onto the pitted PI surface and photolithography was performed to define the patterns of conductors and electrode points (the diameter of the electrode point pattern was slightly larger than the pits, set at 34 μm). Then, a 10 nm thick layer of titanium (Ti, as an adhesion layer) and a 300 nm thick layer of gold (Au, as a conductive layer) were sequentially deposited using electron beam evaporation. The sample was then immersed in a dedicated lift solution and subjected to ultrasonic-assisted lift-off to remove the photoresist and the metal covering it, retaining only the Ti / Au bilayer metal in the patterned area. At this point, the metal electrode points perfectly filled the pits, and because their diameter was larger than the pits, some of their edges overlapped the PI surface surrounding the pits. The lower surface of the electrode points was essentially on the same plane as the lower surface of the first PI layer.

[0047] S5: Forming the second polymer insulating encapsulation layer (corresponding to...) Figure 2 e): The PI-2611 precursor was spin-coated again on the entire sample surface, with the same spin coating parameters and curing process as step S2, forming a second polymer insulating encapsulation layer with a thickness of approximately 3 ± 0.2 μm, which completely encapsulates and insulates the metal wires.

[0048] S6: Form patterned openings to expose and anchor the upper surface of the electrode points (corresponding to...) Figure 2 f): Photolithography and RIE etching are performed again on the second PI layer. The mask used in this study is designed with a grid pattern, with a grid line width of 5 μm. The RIE etching conditions are similar to those in step S3, but the etching time must be strictly controlled to ensure that the upper surface of the underlying gold electrode points is exposed. After etching, approximately 70% of the upper surface area of ​​the electrode points is exposed through the grid openings, while the remaining 30% is covered and supported by the unetched second PI layer (i.e., the grid lines). This portion of the second PI layer constitutes a mechanical anchoring structure for the electrode points, greatly enhancing their stability.

[0049] S7: Remove the sacrificial layer to release the double-sided electrode structure (corresponding to...) Figure 2 g): Figure 1 This is a partial three-dimensional structural diagram of the double-sided flexible neural electrode in an embodiment of the present invention, showing the structure in which the lower surface of the electrode point is fully exposed and the upper surface is partially exposed and anchored through a mesh-like opening.

[0050] The sample is immersed in a specialized aluminum etching solution (such as ferric chloride). The aluminum sacrificial layer is gradually dissolved, eventually releasing the integral flexible neural electrode, composed of the first PI layer, the metal pattern layer, and the second PI layer, from the silicon substrate. At this point, the lower surface of the electrode point is fully exposed. Thus, a double-sided flexible neural electrode with a fully exposed lower surface and an upper surface partially exposed and anchored through a mesh-like opening is fabricated (corresponding to...). Figure 2 h), as attached Figure 3 Optical microscope images a and 3b are shown.

[0051] To further reduce the impedance at the electrode-tissue interface, the released electrode can be electrochemically modified. The electrode was connected to an electrochemical workstation as the working electrode, and a constant current method was used in a mixed electrolyte of 0.05 M chloroplatinic acid (H₂PtCl₆) and 0.5 M sodium sulfate (Na₂SO₄) at -0.1 mA / cm². 2 Deposition was performed at a current density for 300 seconds. Since both the upper and lower surfaces of the electrode point were exposed to the electrolyte, platinum black (Pt Black) could be deposited synchronously and uniformly on the exposed surfaces of the electrode point, as shown in the attached image. Figure 4 As shown.

[0052] Impedance testing was performed on the electrode, and the results are shown in the attached figure. Figure 5 As shown, at a standard physiological signal frequency of 1 kHz, the impedance of the platinum black-modified bifacial electrode is around 20 kΩ, which is significantly lower than that of a conventional electrode of the same size with only one side exposed (typically >35 kΩ), demonstrating its potential in improving the signal-to-noise ratio.

[0053] Example 2: Enhanced bifacial flexible neural electrodes with a three-dimensional complementary anchoring structure This embodiment is an optimized version of embodiment 1. The core improvement lies in the complementary pattern design of the pits in the first polymer insulating layer and the openings in the second polymer insulating encapsulation layer, which realizes the three-dimensional mechanical anchoring of the electrode points and aims to solve the long-term stability problem that may occur in the electrode points under extreme physiological conditions.

[0054] The overall process of this embodiment is the same as that of Embodiment 1. The core difference lies in the photolithography mask design in steps S3 and S6 to achieve complementary patterns. For the specific structure, please refer to the appendix. Figure 6 .

[0055] S3': Define and etch pits with complementary patterns: In this step, the photomask pattern used is not a simple array of circular vias, but rather designed as a "reverse grid" or "island lattice." For example, the mask pattern is a 5 μm linewidth grid, where the grid lines are light-blocking areas and the square openings between the grids are light-transmitting areas. After photolithography and RIE etching, the area below the grid lines is etched away on the first PI layer, while the grid lines themselves and the square "islands" surrounded by the grid are retained. Similarly, this step must be etched to the bottom to expose the aluminum sacrificial layer. This forms a basic structure that complements the subsequent encapsulation layer pattern.

[0056] S4: Fabrication of the metal pattern layer: This step is the same as in Example 1. The metal electrode points will fill and cover these etched "grooves" and the retained "islands".

[0057] S6': Forms a patterned opening that complements the underlying pit: In this step, the mask pattern used to etch the second polymer insulating encapsulation layer (upper insulating layer) is designed to be completely complementary in spatial space to the pattern in S3'. That is, the upper mask pattern has its grid lines facing the "island" areas of the lower first PI layer that are preserved, while the upper opening areas face the "groove" areas of the lower layer that are etched away.

[0058] Through the above complementary pattern design, three-dimensional, omnidirectional mechanical anchoring of the electrode points is achieved: The upper surface of the electrode point is anchored by the grid lines of the second PI layer (upper insulating layer).

[0059] The lower surface of the electrode points is anchored by “islands” preserved by the first PI layer (lower insulating layer).

[0060] The key innovation of this embodiment lies in the fact that the anchoring areas of the upper and lower layers (i.e., the grid lines of the upper layer and the "islands" of the lower layer) are aligned vertically, and the exposed areas (the openings of the upper layer and the "grooves" of the lower layer) are also aligned. This design allows the upper and lower surfaces of the electrode points to form a staggered interlocking with the polymer insulating layer with the maximum area, together constituting a robust three-dimensional mechanical anchoring network, as shown in the attached figure. Figure 6 As shown in the schematic diagram, this structure in this embodiment completely avoids any "suspended" areas at the electrode points, effectively resisting the shear stress generated by tissue micromovement after implantation, thereby significantly improving the mechanical reliability and service life of the device during long-term implantation.

[0061] In summary, this invention, through ingenious process design, particularly the independent or coordinated control of the patterns of the upper and lower insulating layers, successfully fabricates a high-performance, highly stable double-sided flexible neural electrode. Those skilled in the art will understand that modifications and variations can be made to the above embodiments without departing from the principles and spirit of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A double-sided flexible neural electrode, characterized in that, Comprise: a flexible polymer substrate, which is composed of a first polymer insulation layer and a second polymer insulation encapsulation layer; a metal pattern layer embedded in the flexible polymer substrate, which comprises a wire and an electrode point electrically connected with the wire; wherein the electrode point has a double-sided exposed structure, the lower surface of which is coplanar with the lower surface of the first polymer insulation encapsulation layer, forming a first biological contact interface, and the upper surface of which is exposed through a patterned opening on the second polymer insulation encapsulation layer, forming a second biological contact interface; and the second polymer insulation encapsulation layer forms a support structure above the electrode point, which is in contact with the upper surface of the electrode point for mechanically anchoring the electrode point.

2. The dual-sided flexible neural electrode of claim 1, wherein, The patterned opening is in the form of one or more of a regular grid, a circular hole array, and a honeycomb.

3. The dual-sided flexible neural electrode of claim 1, wherein, The exposed area of the upper surface of the electrode point accounts for 20% to 90% of the total area of the upper surface of the electrode point.

4. The dual-sided flexible neural electrode of claim 1, wherein, The electrode point is used for synchronous recording or stimulation of neural electrical activity from both sides thereof.

5. The dual-sided flexible neural electrode of claim 1, wherein, The first polymer insulation layer forms a pit structure below the electrode point, which is complementary to the relief form of the electrode point; The pit structure and the patterned opening on the second polymer insulation encapsulation layer are complementary in spatial distribution, together constituting a three-dimensional mechanical anchoring structure for the electrode point, to avoid the electrode point from having a suspended area.

6. A method of manufacturing a double-sided flexible neural electrode as claimed in any one of claims 1 to 5, characterized in that, Comprise the following steps: S1, providing a sacrificial layer; S2, forming a first polymer insulation layer on the sacrificial layer; S3, etching at least one pit on the first polymer insulation layer; S4, preparing a metal pattern layer on the first polymer insulation layer with the pit etched thereon, which comprises a wire and an electrode point electrically connected with the wire, wherein the electrode point is filled in the pit; S5, forming a second polymer insulation encapsulation layer on the metal pattern layer; S6, forming a patterned opening on the second polymer insulation encapsulation layer in the region corresponding to the electrode point, removing the second polymer insulation encapsulation layer in the opening pattern region by etching process, so that the upper surface of the electrode point is partially exposed, and the second polymer insulation encapsulation layer not etched serves as a support structure in contact with the surface of the electrode point below, for mechanically anchoring the electrode point; S7, removing the sacrificial layer to release a flexible electrode structure, so that the lower surface of the electrode point is exposed, forming a double-sided electrode structure.

7. The method of claim 6, wherein the method further comprises: After S7, further comprise the following process: simultaneously modifying a low-impedance material layer on the exposed upper and lower surfaces of the electrode point by electrochemical deposition.

8. The method of claim 7, wherein the method further comprises: The low-impedance material layer is a conductive polymer selected from one of PEDOT:PSS, platinum black, titanium nitride, and iridium oxide.

9. The method of claim 6, wherein the method further comprises: In S3, a reactive ion etching process is used to etch the pit on the first polymer insulation layer; In S6, a reactive ion etching process is used to etch the pattern with openings on the second polymer insulation encapsulation layer.

10. The method of claim 6, wherein the method further comprises: The materials of the first polymer insulation layer and the second polymer insulation encapsulation layer are selected from one of polyimide, parylene, benzocyclobutene, and SU-8 photoresist.

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