Planar electrode for spinal cord electrical stimulation and preparation method thereof

Abstract

The invention provides a planar electrode for spinal cord electrical stimulation and a preparation method thereof, and belongs to the technical field of medical instruments, and specifically, the planar electrode comprises a flexible substrate, electrode stimulation points, a conductive circuit, a bonding pad and a flexible insulating layer; a modification layer is deposited on the upper surface of the electrode stimulation point, the modification layer forms a grass-shaped morphology with forest leaves, and the modification layer is a platinum layer or a platinum-iridium alloy layer. A platinum layer or a platinum-iridium alloy layer is adopted as a modification layer, the effect of reducing impedance can be achieved, compared with a traditional plane morphology, the grass-shaped morphology with the forest blades can greatly increase the contact area between a film layer and tissue, the impedance is effectively reduced, dissipation of current on an electrode and a biological tissue interface can be reduced through the low impedance, and the service life of the electrode and the biological tissue interface is prolonged. Charge injection efficiency is improved, heating is reduced, tissue thermal damage is avoided, meanwhile, the platinum-iridium alloy material is reversible in chemical reaction in the electrical stimulation process, and toxic substances or material loss caused by the reaction cannot be generated.

Description

Technical Field

[0001] The present application relates to the field of medical device technology, and in particular to a planar electrode for spinal cord electrical stimulation and a method for preparing the same. Background Art

[0002] Spinal cord stimulation is a neuromodulation technology that implants electrodes into the patient's spinal cord and applies a certain current to stimulate the spinal cord. This technology has been widely used to treat spinal cord injuries, intractable pain, stroke and other diseases.

[0003] The electrode is one of the core components of the spinal cord stimulation system, and its performance directly affects the treatment effect. Traditional cylindrical electrodes have poor flexibility and large size. After implantation, they will compress the spinal cord and affect the patient's comfort. The electrode points have poor conformal contact with tissues and are easily displaced, affecting the accuracy of stimulation. With the development of medicine and materials science, the design of new spinal cord stimulation electrodes is gradually developing towards better flexibility, smaller size, higher biocompatibility, easier implantation, and more precise stimulation.

[0004] Although spinal cord stimulation has been used clinically for many years, the existing technology still has some shortcomings: 1) high electrode impedance, poor charge injection capability, and severe heat generation; 2) poor electrode flexibility and large size, which will compress the spinal cord after implantation, and poor conformal contact between the electrode points and tissues; 3) poor biocompatibility, and long-term use may cause biological rejection reactions; 4) high production costs. Summary of the invention

[0005] The purpose of the present application is to provide a planar electrode for spinal cord electrical stimulation, aiming to solve the technical problems of high electrode impedance, poor charge injection capability and severe heat generation of the electrical stimulation electrode in the related art.

[0006] Additional aspects and advantages of the present application will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the present application.

[0007] According to a first aspect of the present application, there is provided a planar electrode for spinal cord electrical stimulation, comprising:

[0008] Flexible substrate, electrode stimulation points, conductive circuits, pads and flexible insulating layer;

[0009] The electrode stimulation points are arranged on the flexible substrate, and the electrode stimulation points are connected to the pads through the conductive lines;

[0010] The flexible insulating layer at least covers the electrode area on the upper surface of the electrode except the electrode stimulation point and the pad;

[0011] A modification layer is deposited on the upper surface of the electrode stimulation point, and the modification layer forms a grass-like morphology with a forest of leaves. The modification layer is a platinum layer or a platinum-iridium alloy layer.

[0012] In an exemplary embodiment of the present application, the thickness of the modification layer is 100-800 nm.

[0013] In an exemplary embodiment of the present application, the electrode stimulation point includes a first adhesion layer, a gold layer and a second adhesion layer from bottom to top, and the modification layer is deposited on the upper surface of the second adhesion layer.

[0014] In an exemplary embodiment of the present application, the first adhesion layer and the second adhesion layer are titanium layers or chromium layers with a thickness ranging from 5 to 50 nm; and / or, the gold layer has a thickness ranging from 50 nm to 20 μm; and / or, the modification layer has a thickness ranging from 100 to 800 nm.

[0015] In an exemplary embodiment of the present application, the electrode stimulation point is circular in shape and is smoothly connected to the conductive circuit.

[0016] In an exemplary embodiment of the present application, the flexible insulating layer only covers the electrode area on the upper surface of the electrode except the electrode stimulation point and the pad; or, the flexible insulating layer covers the electrode area on the entire electrode surface except the electrode stimulation point and the pad.

[0017] In an exemplary embodiment of the present application, the material of the flexible insulating layer is polyparaxylene; and / or the thickness of the flexible insulating layer is in the range of 1-20 μm.

[0018] In an exemplary embodiment of the present application, surgical suture holes are provided on both sides of the flexible substrate.

[0019] According to a second aspect of the present application, there is provided a method for preparing the planar electrode for spinal cord electrical stimulation as described above, comprising the following steps:

[0020] preparing a flexible substrate layer;

[0021] Processing a photoresist structure having electrode stimulation points, conductive circuits, and pad patterns on the flexible substrate layer;

[0022] Electrode stimulation points are deposited at the positions of the electrode stimulation point patterns, and a modification layer is deposited on the upper surfaces of the electrode stimulation points, so that the modification layer forms a grass-like morphology with a forest of leaves.

[0023] In an exemplary embodiment of the present application, the step of forming the modified layer into a grass-like morphology with a forest of leaves comprises:

[0024] The photoresist structure is arranged above the platinum-iridium alloy evaporation source, and an angle θ is formed between the surface of the photoresist structure and the axis of the platinum / platinum-iridium alloy evaporation source;

[0025] A platinum / platinum-iridium alloy evaporation source evaporates to form platinum / platinum-iridium alloy particles. The evaporated platinum / platinum-iridium alloy particles are deposited on the surface of the electrode stimulation point pattern position of the photoresist structure. The platinum / platinum-iridium alloy particles form random islands on the surface of the electrode stimulation point pattern position, forming a shielding shadow effect on subsequent particles reaching the surface of the electrode stimulation point pattern position, making the islands higher and higher until a grass-like morphology with uneven heights is formed.

[0026] In an exemplary embodiment of the present application, the angle θ ranges from 10° to 80°.

[0027] In an exemplary embodiment of the present application, the step of preparing the flexible substrate layer includes: preparing a layer of polyimide on a silicon-based substrate; and / or,

[0028] The step of processing a photoresist structure having electrode stimulation points, conductive circuits, and pad patterns on the flexible substrate layer includes: spin coating photoresist on polyimide, and sequentially performing photolithography and development to process a positive photoresist structure having electrode stimulation points, conductive circuits, and pad patterns.

[0029] In an exemplary embodiment of the present application, the following steps are also included:

[0030] A titanium layer, a gold layer, a titanium layer, and a platinum / platinum-iridium alloy layer are sequentially deposited by an electron beam evaporation thin film deposition method. After the deposition is completed, the photoresist is dissolved and stripped using acetone to obtain a conductive pattern on the polyimide layer, wherein the conductive pattern includes electrode stimulation points, conductive circuits, and pads whose upper surface is modified with a platinum / platinum-iridium alloy layer;

[0031] Cut the electrode contour to form the electrode shape;

[0032] The electrode semi-finished product on the silicon-based substrate is released from the silicon-based substrate by using the method of electrolytic silicon;

[0033] Depositing polyparaxylene on the upper surface of the electrode semi-finished product by chemical vapor deposition, and pre-wrapping the pad with tape before deposition;

[0034] A hollow stainless steel mask is used to cover the electrode, and the hollow area corresponds to the size, shape, and position of the electrical stimulation point. The polyparaxylene below the hollow area of ​​the stainless steel mask is etched away using a reactive ion etching method to expose the conductive platinum / platinum-iridium alloy;

[0035] The prepared electrode was assembled with the adapter plate and the interface protective shell, and the gap on the protective shell was filled and encapsulated with polydimethylsiloxane to complete the preparation of the planar electrode for spinal cord electrical stimulation.

[0036] The exemplary embodiments of the present application may have some or all of the following beneficial effects:

[0037] The planar electrode for spinal cord electrical stimulation provided in the example embodiment of the present application includes a flexible substrate, an electrode stimulation point, a conductive circuit, a pad and a flexible insulating layer, wherein the electrode stimulation point is arranged on the flexible substrate, the electrode stimulation point is connected to the pad through a conductive circuit, the flexible insulating layer covers at least the electrode area on the upper surface of the electrode except the electrode stimulation point and the pad, and a modifying layer is deposited on the upper surface of the electrode stimulation point, the modifying layer forms a grass-like morphology with a forest of leaves, specifically, the modifying layer is a platinum layer or a platinum-iridium alloy layer. First, the planar electrode formed by structures such as a flexible substrate and a flexible insulating layer has a certain degree of flexibility. Compared with traditional columnar electrodes, the electrode is more flexible, smaller in size, and has good commonality contact with tissues. Second, the use of a platinum layer or a platinum-iridium alloy layer as a modified layer can reduce impedance. The grass-like morphology with leaves can greatly increase the contact area between the membrane layer and the tissue compared to the traditional planar morphology, effectively reducing impedance. Lower impedance can reduce the dissipation of current at the interface between the electrode and biological tissue, improve the charge injection efficiency, reduce heat, and avoid thermal damage to the tissue. At the same time, the chemical reaction of the platinum-iridium alloy material during electrical stimulation is reversible, and will not react to produce toxic substances or cause material loss. Third, a flexible insulating layer is used to insulate the electrode area outside the electrode stimulation point and the pad. The flexible insulating layer is made of polyparaxylene material. Polyparaxylene is a material with good biosafety certified by the US FDA, has better biocompatibility, and can be implanted for long-term use.

[0038] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The drawings herein are incorporated into the specification and constitute a part of the specification, illustrate embodiments consistent with the present application, and together with the specification are used to explain the principles of the present application. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0040] Figure 1 A top view of a planar electrode for spinal cord electrical stimulation in Example 1 of the present application is shown;

[0041] Figure 2A side view of a planar electrode for spinal cord electrical stimulation in Example 1 of the present application is shown;

[0042] Figure 3 A side view showing a flexible insulating layer covering the entire electrode in Example 1 of the present application is shown;

[0043] Figure 4 A schematic diagram showing the material layering of the electrode stimulation point of the electrical stimulation electrode in Example 1 of the present application is shown;

[0044] Figure 5 A schematic diagram of the structure of the angle formed between the platinum / platinum-iridium alloy evaporation source and the electrode sample in Example 2 of the present application is shown.

[0045] Description of reference numerals:

[0046] 1. Flexible substrate; 2. Electrode stimulation point; 3. Surgical suture hole; 4. Conductive circuit; 5. Solder pad; 6. Reinforcement plate; 7. Flexible insulation layer;

[0047] 24. First adhesion layer; 25. Gold layer; 26. Second adhesion layer; 27. Modification layer; 28. Workbench; 29. ​​Electrode sample; 30. Evaporation source. DETAILED DESCRIPTION

[0048] Example embodiments will now be described more fully with reference to the accompanying drawings. However, the example embodiments can be implemented in a variety of forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that the present application will be comprehensive and complete and fully convey the concepts of the example embodiments to those skilled in the art. The same reference numerals in the figures represent the same or similar structures, and thus their detailed descriptions will be omitted. In addition, the drawings are only schematic illustrations of the present application and are not necessarily drawn to scale.

[0049] Although relative terms such as "upper" and "lower" are used in this specification to describe the relative relationship of one component of the diagram to another component, these terms are used in this specification only for convenience, such as according to the direction of the examples in the drawings. It is understood that if the device of the diagram is turned upside down, the component described as "upper" will become the component "lower". When a structure is "on" other structures, it may mean that the structure is formed integrally on the other structure, or that the structure is "directly" disposed on the other structure, or that the structure is "indirectly" disposed on the other structure through another structure.

[0050] The terms "a", "an", "the" and "at least one" are used to indicate the presence of one or more elements / components / etc.; the terms "including" and "having" are used to express an open-ended inclusive meaning and mean that additional elements / components / etc. may exist in addition to the listed elements / components / etc.; the terms "first" and "second" are used merely as labels and are not intended to limit the quantity of their objects.

[0051] Example 1

[0052] This embodiment provides a specific implementation of a planar electrode for spinal cord electrical stimulation, such as Figure 1 , Figure 2 and Figure 3 As shown, it includes a flexible substrate 1, an electrode stimulation point 2, a conductive line 4, a pad 5 and a flexible insulating layer 7, wherein the electrode stimulation point 2 is arranged on the flexible substrate 1, the electrode stimulation point 2 is connected to the pad 5 through the conductive line 4, the flexible insulating layer 7 covers at least the electrode area on the upper surface of the electrode except the electrode stimulation point 2 and the pad 5, and a modification layer 27 is deposited on the upper surface of the electrode stimulation point 2, and the modification layer 27 forms a grass-like morphology with leaves standing in a forest, and specifically, the modification layer 27 is a platinum layer or a platinum-iridium alloy layer. Using a platinum layer or a platinum-iridium alloy layer as the modification layer 27 can play a role in reducing impedance. Compared with the traditional planar morphology, the grass-like morphology with leaves standing in a forest can greatly increase the contact area between the membrane layer and the tissue, effectively reducing impedance, and lower impedance can reduce the dissipation of current at the interface between the electrode and the biological tissue, improve the efficiency of charge injection, reduce heat, and avoid thermal damage to the tissue. At the same time, the chemical reaction of the platinum-iridium alloy material is reversible during the electrical stimulation process, and will not react to produce toxic substances or cause material loss.

[0053] Furthermore, the thickness of the modification layer 27 is 100-800 nm. In this embodiment, the thickness of the modification layer 27 is preferably 300 nm.

[0054] In this embodiment, Figure 4 As shown, the electrode stimulation point 2 includes a first adhesion layer 24, a gold layer 25, and a second adhesion layer 26 from bottom to top, and a modification layer 27 is deposited on the upper surface of the second adhesion layer 26. Further, the first adhesion layer 24 and the second adhesion layer 26 are titanium layers or chromium layers, and the thickness ranges from 5 to 50 nm. Further, the gold layer 25 is used as the main conductive material, and the thickness range of the gold layer 25 is 50 nm to 20 μm.

[0055] In this embodiment, the electrode stimulation point 2 is the discharge area when electrical stimulation is applied. The electrode stimulation point 2 is circular in shape and smoothly connected to the conductive circuit 4 without sharp corners to avoid local tissue damage caused by tip discharge during electrical stimulation.

[0056] In this embodiment, the flexible insulating layer 7 only covers the electrode area on the upper surface of the electrode except the electrode stimulation point 2 and the pad 5. The flexible insulating layer 7 insulates the conductive circuit 4 to prevent the conductive circuit 4 from direct contact with the biological tissue and to prevent the conductive circuit 4 from discharging and stimulating the biological tissue during electrical stimulation. The flexible insulating layer 7 only covers the upper surface of the electrode to minimize the number of material layers and reduce the overall thickness of the electrode, thereby reducing the bending stiffness of the electrode and improving the flexibility of the electrode.

[0057] In some other embodiments, the flexible insulating layer 7 covers the entire electrode surface except the electrode stimulation point 2 and the pad 5. The flexible insulating layer 7 completely covers the entire electrode surface except the electrode stimulation point 2 and the pad 5, so that the electrode will not separate from each other when it is immersed in tissue fluid for a long time, thereby ensuring the structural stability of the electrode during long-term implantation.

[0058] Furthermore, the material of the flexible insulating layer 7 is polyparaxylene, which is a long-term implantable biosafety material certified by the US FDA and has good biocompatibility. The thickness of the flexible insulating layer 7 is 1-20 μm.

[0059] In this embodiment, the flexible substrate 1 is polyimide or polyparaxylene, and has a thickness ranging from 1 to 20 μm. The material and thickness of the flexible substrate 1 ensure that it has good flexibility, can be bent, folded, and fits well with the surface of biological tissue.

[0060] In this embodiment, surgical suture holes 3 are provided on both sides of the flexible substrate 1. During the implantation operation, the surgical suture holes 3 are sutured with biological tissues by medical sutures to ensure that the position of the electrode is relatively fixed after implantation into the biological body, thereby avoiding displacement or misalignment of the electrode.

[0061] In this embodiment, the electrode stimulation point 2 and the pad 5 are electrically connected through the conductive line 4. The material of the conductive line 4 is a metal material with stable chemical properties and good conductivity, such as gold, platinum, etc. The thickness of the conductive line 4 ranges from 50nm-20μm, and the line width ranges from 1-100μm. Further, the pad 5 is the position on the electrical stimulation electrode connected to the rear-end circuit board. The pad 5 can be electrically connected to the rear-end circuit board by welding, mechanical clamping, anisotropic conductive adhesive bonding, etc. The material of the pad 5 is a metal material with good conductivity, such as copper, gold, platinum, etc., the thickness ranges from 50nm-20μm, and the line width ranges from 50-500μm.

[0062] In this embodiment, a reinforcing plate 6 is provided at the tail of the electrical stimulation electrode, and the reinforcing plate 6 can enhance the mechanical strength of the pad 5 at the tail of the electrode, so as to facilitate reliable fixation and connection between the pad 5 and the rear circuit board. Further, the reinforcing plate 6 has the same width as the tail of the electrode, a thickness range of 200 μm-1 mm, and has sufficient mechanical strength and rigidity. Specifically, the reinforcing plate 6 is made of polyimide or stainless steel, and is bonded to the flexible substrate 1 by an adhesive. The reinforcing plate 6 is bonded to the bottom layer of the flexible substrate 1, and the pad 5 is located on the top layer of the flexible substrate 1.

[0063] Example 2

[0064] This embodiment provides a specific implementation method of a method for preparing a planar electrode for spinal cord electrical stimulation, including the planar electrode for spinal cord electrical stimulation in Example 1, and also includes the following steps: preparing a flexible substrate 1 layer; processing a photoresist structure having a pattern of electrode stimulation points 2, conductive lines 4, and pads 5 on the flexible substrate 1 layer; depositing electrode stimulation points 2 at the pattern positions of the electrode stimulation points 2, and depositing a modification layer 27 on the upper surface of the electrode stimulation points 2, and making the modification layer 27 form a grass-like morphology with leaves standing in a forest.

[0065] In this embodiment, the step of forming the modified layer 27 into a grass-like morphology with a forest of leaves includes: setting a photoresist structure above a platinum / platinum-iridium alloy evaporation source 30, and there is an angle θ between the surface of the photoresist structure and the axis of the platinum / platinum-iridium alloy evaporation source 30; the platinum / platinum-iridium alloy evaporation source 30 evaporates to form platinum / platinum-iridium alloy particles, and the platinum / platinum-iridium alloy particles are deposited on the surface of the electrode stimulation point 2 pattern position of the photoresist structure, and the platinum / platinum-iridium alloy particles form random islands on the surface of the electrode stimulation point 2 pattern position, forming a shielding shadow effect on the particles that subsequently arrive at the surface of the electrode stimulation point 2 pattern position, so that the islands become higher and higher until a grass-like morphology with uneven heights is formed.

[0066] Furthermore, the angle θ ranges from 10° to 80°.

[0067] Specifically, Figure 5 As shown, a photoresist structure forming electrode sample 29 is set on the surface of a rotating workbench 28 , and a platinum / platinum-iridium alloy evaporation source 30 is placed under the rotating workbench 28 .

[0068] In this embodiment, the step of preparing a flexible substrate layer 1 includes preparing a layer of polyimide on a silicon-based substrate; the step of processing a photoresist structure having a pattern of electrode stimulation points 2, conductive circuits 4, and pads 5 on the flexible substrate layer 1 includes spin coating photoresist on the polyimide, and performing photolithography and development in sequence to process a positive photoresist structure having a pattern of electrode stimulation points 2, conductive circuits 4, and pads 5.

[0069] In this embodiment, it also includes using an electron beam evaporation thin film deposition method to deposit a titanium layer, a gold layer 25, a titanium layer, and a platinum / platinum-iridium alloy layer on the electrode stimulation point 2 in sequence, and using acetone to dissolve and peel off the photoresist after the deposition is completed to obtain a conductive pattern on the polyimide layer, the conductive pattern including the electrode stimulation point 2, the conductive circuit 4 and the pad 5 whose upper surface is modified with a platinum / platinum-iridium alloy layer; cutting the electrode contour to cut out the electrode shape; using an electrolytic silicon method to release the electrode semi-finished product on the silicon-based substrate from the silicon-based substrate; using a chemical vapor deposition method to deposit polyparaxylene on the upper surface of the electrode semi-finished product, and pre-wrapping the pad 5 with tape before deposition; using a hollow stainless steel mask to cover the electrode, the hollow area corresponds to the size, shape and position of the electrical stimulation point, and using a reactive ion etching method to etch and remove the polyparaxylene below the hollow area of ​​the stainless steel mask to expose the conductive platinum / platinum-iridium alloy; assembling the prepared electrode with an adapter plate and an interface protective shell, and using polydimethylsiloxane to fill and encapsulate the gap on the protective shell to prepare a planar electrode for spinal cord electrical stimulation.

[0070] The above-mentioned electrode processing technology is a micro-nano processing technology with low processing cost. The electrode materials all have a micrometer or nanometer thickness, which saves materials.

[0071] The following is an explanation of the above method through a specific case:

[0072] A 10 μm thick polyimide layer was prepared by spin coating on a silicon wafer;

[0073] Spin-coat photoresist on the polyimide layer, then perform photolithography and development processes in sequence to produce a positive photoresist structure having patterns of electrode stimulation points 2, conductive circuits 4, and pads 5;

[0074] Using an electron beam evaporation thin film deposition method, 10 nm titanium, 100 nm gold, 10 nm titanium, and 300 nm platinum / platinum-iridium alloy are sequentially deposited, and the platinum / platinum-iridium alloy layer forms a grass-like morphology with uneven heights. After the deposition is completed, the photoresist is dissolved and stripped using acetone to obtain a conductive pattern on the polyimide layer;

[0075] Cut the electrode contour using laser cutting to cut out the electrode shape and surgical suture hole 3;

[0076] The electrode semi-finished product on the silicon wafer is released from the silicon wafer by electrolyzing silicon;

[0077] Adhere a reinforcing plate 6 to the tail of the semi-finished electrode;

[0078] Deposit polyparaxylene with a thickness of 2 μm using a chemical vapor deposition method. Before deposition, wrap the pad 5 with a tape to prevent the deposited polyparaxylene from insulating the pad 5. After the deposition is completed, tear off the tape wrapping the pad 5.

[0079] A hollow stainless steel mask plate is used to cover the electrode. The hollow area of ​​the stainless steel mask plate corresponds to the size, shape and position of the electrode stimulation point 2. The polyparaxylene under the hollow area of ​​the stainless steel mask plate is etched away using a reactive ion etching method to expose a conductive platinum / platinum-iridium alloy layer to obtain a planar electrode for spinal cord electrical stimulation.

[0080] Those skilled in the art will easily think of other embodiments of the present application after considering the specification and practicing the embodiments of the present application. The present application is intended to cover any modification, use or adaptation of the present application, which follows the general principles of the present application and includes common knowledge or customary techniques in the art that the present application does not apply for. The specification and embodiments are only regarded as exemplary, and the true scope and spirit of the present application are pointed out by the appended claims.

Claims

1. A planar electrode for spinal cord electrical stimulation, characterized in that: include: Flexible substrate, electrode stimulation points, conductive circuits, pads and flexible insulating layer; The electrode stimulation points are arranged on the flexible substrate, and the electrode stimulation points are connected to the pads through the conductive lines; The flexible insulating layer at least covers the electrode area on the upper surface of the electrode except the electrode stimulation point and the pad; A modification layer is deposited on the upper surface of the electrode stimulation point, and the modification layer forms a grass-like morphology with a forest of leaves. The modification layer is a platinum layer or a platinum-iridium alloy layer.

2. The planar electrode for spinal cord electrical stimulation according to claim 1, characterized in that: The thickness of the modified layer is 100-800 nm.

3. The planar electrode for spinal cord electrical stimulation according to claim 1, characterized in that: The electrode stimulation point comprises, from bottom to top, a first adhesion layer, a gold layer, and a second adhesion layer, and the modification layer is deposited on the upper surface of the second adhesion layer.

4. The planar electrode for spinal cord electrical stimulation according to claim 3, characterized in that: The first adhesion layer and the second adhesion layer are titanium layers or chromium layers with a thickness ranging from 5 to 50 nm; and / or, the gold layer has a thickness ranging from 50 nm to 20 μm; and / or, the modification layer has a thickness ranging from 100 to 800 nm.

5. The planar electrode for spinal cord electrical stimulation according to any one of claims 1 to 4, characterized in that: The electrode stimulation point is circular in shape and is smoothly connected to the conductive circuit.

6. The planar electrode for spinal cord electrical stimulation according to any one of claims 1 to 4, characterized in that: The flexible insulating layer only covers the electrode area on the upper surface of the electrode except the electrode stimulation point and the pad; or, the flexible insulating layer covers the electrode area on the entire electrode surface except the electrode stimulation point and the pad.

7. The planar electrode for spinal cord electrical stimulation according to any one of claims 1 to 4, characterized in that: The material of the flexible insulating layer is polyparaxylene; and / or the thickness of the flexible insulating layer is in the range of 1-20 μm.

8. The planar electrode for spinal cord electrical stimulation according to any one of claims 1 to 4, characterized in that: Surgical suture holes are arranged on both sides of the flexible substrate.

9. A method for preparing a planar electrode for spinal cord electrical stimulation comprising any one of claims 1 to 8, characterized in that: The following steps are involved: preparing a flexible substrate layer; Processing a photoresist structure having electrode stimulation points, conductive circuits, and pad patterns on the flexible substrate layer; Electrode stimulation points are deposited at the positions of the electrode stimulation point patterns, and a modification layer is deposited on the upper surfaces of the electrode stimulation points, so that the modification layer forms a grass-like morphology with a forest of leaves.

10. The method for preparing a planar electrode for spinal cord electrical stimulation according to claim 9, characterized in that: The step of forming the modified layer into a grass-like morphology with a forest of leaves comprises: The photoresist structure is arranged above the platinum-iridium alloy evaporation source, and an angle θ is formed between the surface of the photoresist structure and the axis of the platinum / platinum-iridium alloy evaporation source; A platinum / platinum-iridium alloy evaporation source evaporates to form platinum / platinum-iridium alloy particles. The evaporated platinum / platinum-iridium alloy particles are deposited on the surface of the electrode stimulation point pattern position of the photoresist structure. The platinum / platinum-iridium alloy particles form random islands on the surface of the electrode stimulation point pattern position, which form a shielding shadow effect on subsequent particles reaching the surface of the electrode stimulation point pattern position, making the islands higher and higher until a grass-like morphology with uneven heights is formed.

11. The planar electrode for spinal cord electrical stimulation according to claim 10, characterized in that: The angle θ ranges from 10° to 80°.

12. The method for preparing a planar electrode for spinal cord electrical stimulation according to claim 9, characterized in that: The step of preparing the flexible substrate layer comprises: preparing a layer of polyimide on a silicon-based substrate; and / or, The step of processing a photoresist structure having electrode stimulation points, conductive circuits, and pad patterns on the flexible substrate layer includes: spin coating photoresist on polyimide, and sequentially performing photolithography and development to process a positive photoresist structure having electrode stimulation points, conductive circuits, and pad patterns.

13. The method for preparing a planar electrode for spinal cord electrical stimulation according to claim 12, characterized in that: The following steps are also included: A titanium layer, a gold layer, a titanium layer, and a platinum / platinum-iridium alloy layer are sequentially deposited by an electron beam evaporation thin film deposition method. After the deposition is completed, the photoresist is dissolved and stripped using acetone to obtain a conductive pattern on the polyimide layer, wherein the conductive pattern includes electrode stimulation points, conductive circuits, and pads whose upper surface is modified with a platinum / platinum-iridium alloy layer; Cut the electrode contour to form the electrode shape; The electrode semi-finished product on the silicon-based substrate is released from the silicon-based substrate by using the method of electrolytic silicon; Depositing polyparaxylene on the upper surface of the electrode semi-finished product by chemical vapor deposition, and pre-wrapping the pad with tape before deposition; A hollow stainless steel mask is used to cover the electrode, and the hollow area corresponds to the size, shape, and position of the electrical stimulation point. The polyparaxylene below the hollow area of ​​the stainless steel mask is etched away using a reactive ion etching method to expose the conductive platinum / platinum-iridium alloy; The prepared electrode was assembled with the adapter plate and the interface protective shell, and the gap on the protective shell was filled and encapsulated with polydimethylsiloxane to complete the preparation of the planar electrode for spinal cord electrical stimulation.

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