Pad structure of flexible stimulation electrode and method for manufacturing the same

Abstract

The application describes a pad structure of a flexible stimulation electrode and a preparation method, the pad structure comprising a first insulating layer, a first metal material layer, a second insulating layer, a second metal material layer, a third insulating layer and a central via, wherein the first metal material layer is formed on the first insulating layer; the second insulating layer is formed on the first metal material layer and the first insulating layer; the second metal material layer is formed on the first metal material layer and the second insulating layer; the third insulating layer is formed on the second metal material layer and the second insulating layer; the first insulating layer, the second insulating layer and the third insulating layer are composed of the same material; the central via comprises a first via and a second via, the first via penetrates and exposes the first insulating layer, the first metal material layer and the second metal material layer, and the second via penetrates the third insulating layer. The application simplifies the existing preparation process, and the pad structure can realize the connection between the electrode and the external circuit by using a simple gold ball welding or conductive glue coating process.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of biomedical engineering, in particular to a flexible stimulating electrode pad structure and a preparation method thereof. BACKGROUND

[0002] Artificial vision has a very wide application prospect compared with traditional medical surgery or drugs in helping blind patients to restore vision. Artificial vision refers to a method of using retinal repair technology to implant an integrated circuit chip (visual prosthesis) with biocompatibility into the eye or other specific parts to help the blind to restore vision, that is, different visual prostheses are implanted in different parts, the visual prostheses generate electrical signals, stimulate and activate the visual system, thereby generating nerve impulses, so that the blind or nearly blind patients regain part of the useful vision. According to the implantation and stimulation site of the visual prosthesis, the visual prosthesis is mainly divided into three categories: visual cortex prosthesis, optic nerve prosthesis, and retinal prosthesis (artificial retina or artificial retina biological microelectrode). Direct electrical stimulation of the retina, that is, using the retinal prosthesis, has greater potential for ideal vision, so it has been a hot research topic for domestic and foreign scholars.

[0003] At present, the commonly used manufacturing process based on MEMS (Micro-Electro-Mechanical System) is used to manufacture biological microelectrodes. The biological microelectrodes made of flexible materials such as polyimide (Polyimide), parylene C (Parylene C), polydimethylsiloxane (PDMS, Polydimethylsiloxane) and other polymers as the substrate have good biocompatibility, corrosion resistance, insulation, waterproofness, flexibility, elasticity and stress. Artificial retina biological microelectrodes are generally divided into electrode stimulation parts (electrode sites) and electrode pads. The electrode stimulation part is mainly the working area of the electrode for replacing the retina to obtain light stimulation and generate electrical signals. The electrode pad is used to connect the electrode stimulation part and connect the external circuit to realize the transmission of electrical signals and restore the visual function in the brain nerve through the electrical stimulation of the optic nerve by the external circuit, so that the blind patients can see again.

[0004] A method for preparing a visual prosthesis flexible neural microelectrode pad is disclosed in the prior art document (CN105169554B), which can combine the advantages of two excellent polymer materials, parylene and polyimide, to make the pad part of the visual prosthesis flexible neural microelectrode, while the electrode site and lead part are only packaged with parylene, ensuring the transparency, low permeability and good biocompatibility of the entire electrode, and also ensuring that the pad will not be damaged by high temperature during the welding process. However, in order to realize the connection of the double metal layer, the method in the prior art document needs to introduce a complex electroplating process, and will rely on the deposition material to build mechanical structures or electronic components, and the thickness of the material layer that cannot be seen by an optical microscope will seriously affect the performance of the neural microelectrode.

[0005] In addition, the neural microelectrode in the prior art is usually connected to the external circuit by flip-chip technology, which is mainly applied in high-end devices and high-density packaging fields, and has the advantages of short interconnection line, small parasitic capacitance and internal parasitic inductor, and the I / O pin of the integrated IC can be randomly set on the surface of the integrated IC, and the relative density of the package is high. However, in the flip-chip technology, it is necessary to produce and manufacture bumps on the I / O pin of the integrated IC, but the manufacture of the bumps requires a high or complex process level, which is not conducive to the batch production of biological microelectrodes. SUMMARY

[0006] The present application is proposed in view of the above prior art.

[0007] The present application provides a pad structure of a flexible stimulating electrode and a preparation method, wherein the preparation method is compatible with MEMS, and has the advantages of mature MEMS process, high repeatability, high yield, and easy batch production, while simplifying the preparation process. In addition, the pad structure of the flexible stimulating electrode prepared by the present application can be connected to the external circuit by using simple gold ball welding or conductive glue coating process, whether it is single-layer or multi-layer design. The cross-shaped or plum blossom-shaped combined pad structure can be more reliably connected to the external circuit.

[0008] The first aspect of the present application provides a pad structure of a flexible stimulation electrode, comprising: a first insulating layer, a first metal material layer, a second insulating layer, a second metal material layer, a third insulating layer and a central via, the first metal material layer is formed on the first insulating layer; the second insulating layer is formed on the first metal material layer and the first insulating layer and exposes part of the first metal material layer, the first metal material layer comprises two first adhesive layers and a first conductive layer arranged between the two first adhesive layers; the second metal material layer is formed on the first metal material layer and the second insulating layer, the second metal material layer comprises two second adhesive layers and a second conductive layer arranged between the two second adhesive layers; the third insulating layer is formed on the second metal material layer and the second insulating layer; the first insulating layer, the second insulating layer and the third insulating layer are composed of the same material; the central via comprises a first via and a second via, the first via penetrates and exposes the first insulating layer, the first metal material layer and the second metal material layer, and the second via penetrates the third insulating layer and exposes part of the upper surface of the second conductive layer.

[0009] In this case, the insulating layer can isolate the non-contact part between the metal material layer and the flexible stimulation electrode, the metal material layer can connect the lead wire of the flexible stimulation electrode and the feedthrough structure to form a circuit conduction, in addition, the central via in the pad structure can make the pad structure connect the external circuit by using the gold ball bonding or the conductive glue coating process.

[0010] According to the pad structure of the present application, the cross section of the first via perpendicular to the extension direction of the first via is smaller than the cross section of the second via perpendicular to the extension direction of the second via, and the cross section of the first via is parallel to the cross section of the second via. In this case, the central via formed by the cooperation of the first via and the second via can be more conducive to connecting the pad structure with the external circuit by using the gold ball bonding or the conductive glue coating process. When connecting, the feedthrough structure of the external circuit and the metal conductive layer of the pad structure of the flexible stimulation electrode can be connected by using solder or conductive glue in the first via, and the solder or conductive glue can better adhere to the metal conductive layer of the pad structure of the flexible stimulation electrode through the second via when connecting.

[0011] Optionally, the cross section of the first through hole and the cross section of the second through hole are in one of the following shapes: circle, square, rectangle, ellipse or combined shape formed by superimposing one of the following shapes: cross shape, plum blossom shape, circle, square, rectangle or ellipse. In this case, the pad structure can be manufactured in different shapes according to different production requirements, and the combined shape formed by superimposing one of the following shapes: cross shape, plum blossom shape, circle, square, rectangle or ellipse can make the feedthrough structure of the external circuit more firmly connected with the pad of the flexible stimulation electrode.

[0012] Optionally, the first insulating layer is polyimide with a thickness of 5-6 μm, the second insulating layer is polyimide with a thickness of 1-2 μm, and the third insulating layer is polyimide with a thickness of 5-6 μm. In this case, the three-dimensional multi-layer pad mechanism can be formed by the multi-layer insulating layer, and more wires connecting the flexible stimulation electrode and the pad structure of the flexible stimulation electrode can be arranged in the multi-layer insulating layer. In addition, polyimide has good biocompatibility and mechanical flexibility, which can make the flexible stimulation electrode better implanted in the visual area of the human body.

[0013] Optionally, the area of the first metal material layer is smaller than the first insulating layer, and the area of the second metal material layer is smaller than the second insulating layer. In this case, a plurality of first metal material layers can be formed in the first insulating layer, and a plurality of second metal material layers can be formed in the second insulating layer, i.e. more pad arrays corresponding to the flexible stimulation electrode array are formed.

[0014] Optionally, the first metal material layer is a composite material, the first adhesion layer is a titanium metal layer with a thickness of 30-100 nm, and the first conductive layer is a platinum metal layer with a thickness of 100-300 nm. The interface between the first adhesion layer and the first conductive layer is parallel to the cross section of the first through hole or the cross section of the second through hole. In this case, the first metal material layer is formed by superimposing titanium-platinum-titanium in sequence. The titanium layer can increase the adhesion of the first metal material layer to each insulating layer, and the platinum layer can be connected to the wire or lead of the flexible stimulation electrode and the feedthrough structure of the external circuit as the main conductive medium of the first metal material layer to form a conductive circuit.

[0015] According to the pad structure, optionally, the second metal material layer is a composite material, the second adhesion layer is a titanium metal layer with a thickness of 30-100 nm, the second conductive layer is a platinum metal layer with a thickness of 100-300 nm, and the interface between the second adhesion layer and the second conductive layer is parallel to the cross section of the first via hole or the cross section of the second via hole. In this case, the second metal material layer is formed by sequentially stacking titanium-platinum-titanium, the titanium layer can increase the adhesion of the second metal material layer to each insulating layer, and the platinum layer can be connected to the lead wire or lead line of the flexible stimulation electrode and the feedthrough structure of the external circuit to form a conductive circuit.

[0016] According to the pad structure, optionally, the pad structure is connected to the feedthrough structure by gold wire ball bonding or drop-coating conductive glue, and the feedthrough structure is at least one of a feedthrough ceramic substrate, a feedthrough circuit board, and an integrated circuit. In this case, the gold wire ball bonding or drop-coating conductive glue process is used to connect the pad structure of the flexible stimulation electrode to the feedthrough structure of the external circuit, so that the electrode array of the flexible stimulation electrode can form a complete sensing circuit through the pad structure (or pad array) and the feedthrough structure of the external circuit to realize the function of the artificial retina. In addition, in the preparation process, the gold wire ball bonding or drop-coating conductive glue process is used, so that the complex flip-chip welding process of first making bumps and then welding can be avoided.

[0017] The second aspect of the present application provides a preparation method of a pad structure of a flexible stimulation electrode, comprising:

[0018] The substrate is prepared, and a first insulating layer is formed on the substrate. The first insulating layer is processed by a patterning process to have a first preset channel. A first metal material layer matching the first preset channel is formed on the first insulating layer. The first metal material layer includes two first adhesive layers and a first conductive layer arranged between the two first adhesive layers. A second insulating layer covering the first insulating layer and the first metal material layer is formed on the first insulating layer and the first metal material layer. The second insulating layer is processed by a patterning process to have a second preset channel. A second metal material layer matching the second preset channel is formed on the second insulating layer. The second metal material layer includes two second adhesive layers and a second conductive layer arranged between the two second adhesive layers. A third insulating layer covering the second insulating layer and the second metal material layer is formed on the second metal material layer. A sacrificial layer is formed on the third insulating layer and processed by a patterning process to have a third preset channel. The first insulating layer, the second insulating layer, and the third insulating layer are processed based on the third preset channel to form a fourth preset channel. The sacrificial layer is removed. Part of the second adhesive layer is removed based on the fourth preset channel to expose part of the upper surface of part of the second conductive layer. The substrate is removed to form a central through hole. The central through hole includes a first through hole and a second through hole. The first through hole penetrates and exposes the first insulating layer, the first metal material layer, and the second metal material layer. The second through hole penetrates the third insulating layer and exposes part of the upper surface of part of the second conductive layer.

[0019] In this case, the multilayer pad structure prepared by the preparation method of the pad structure of the flexible stimulation electrode can directly connect the first metal material layer with the second metal material layer, avoiding the dependence on the deposited material for constructing mechanical structures or electronic elements caused by the complex electroplating process. In addition, the preparation method is compatible with MEMS, which can take advantage of the mature MEMS process, high repeatability, high yield, and easy batch production.

[0020] According to the preparation method, optionally, the cross section of the first through hole perpendicular to the extension direction of the first through hole is smaller than the cross section of the second through hole perpendicular to the extension direction of the second through hole, and the cross section of the first through hole is parallel to the cross section of the second through hole; the cross section of the first through hole and the cross section of the second through hole are one of a circle, a square, a rectangle, an ellipse or a combined pattern formed by superimposing one of a circle, a square, a rectangle or an ellipse at the center of a cross or a plum blossom; in this case, the central through hole formed by the cooperation of the first through hole and the second through hole can be more conducive to the connection of the pad structure and the external circuit by gold wire ball welding or conductive glue coating process; when connected, the solder or conductive glue can be used to connect the feedthrough structure of the external circuit and the metal conductive layer of the pad structure of the flexible stimulating electrode through the first through hole, and the solder or conductive glue can be better attached to the metal conductive layer of the pad structure of the flexible stimulating electrode through the second through hole. In addition, the pad structure manufactured according to the matched shape can be adaptively selected according to different production needs, and the combined pattern of the circle, the square, the rectangle or the ellipse superimposed at the center of the cross or the plum blossom can make the connection of the feedthrough structure of the external circuit and the pad of the flexible stimulating electrode more firm.

[0021] According to the preparation method, optionally, the cross section of the first through hole perpendicular to the extension direction of the first through hole is smaller than the cross section of the second through hole perpendicular to the extension direction of the second through hole, and the cross section of the first through hole is parallel to the cross section of the second through hole; the cross section of the first through hole and the cross section of the second through hole are one of a circle, a square, a rectangle, an ellipse or a combined pattern formed by superimposing one of a circle, a square, a rectangle or an ellipse at the center of a cross or a plum blossom; in this case, the central through hole formed by the cooperation of the first through hole and the second through hole can be more conducive to the connection of the pad structure and the external circuit by gold wire ball welding or conductive glue coating process; when connected, the solder or conductive glue can be used to connect the feedthrough structure of the external circuit and the metal conductive layer of the pad structure of the flexible stimulating electrode through the first through hole, and the solder or conductive glue can be better attached to the metal conductive layer of the pad structure of the flexible stimulating electrode through the second through hole. In addition, the pad structure manufactured according to the matched shape can be adaptively selected according to different production needs, and the combined pattern of the circle, the square, the rectangle or the ellipse superimposed at the center of the cross or the plum blossom can make the connection of the feedthrough structure of the external circuit and the pad of the flexible stimulating electrode more firm.

[0022] In this case, the first metal material layer can be formed in a ring shape through the first preset channel, the second metal material layer can be formed in a ring shape through the second preset channel, and the fourth preset channel can be formed into a final central through hole by removing the substrate, the sacrificial layer, and the second adhesive layer on the upper surface of the partial second metal material layer, so that the pad structure of the flexible stimulation electrode can be prepared, and the pad structure can be connected to an external circuit through the central through hole in the pad structure by using a gold ball welding or conductive adhesive coating process.

[0023] According to the preparation method, the patterning process is a process of using a photoresist to develop and expose a predetermined pattern through irradiation or radiation of any one of ultraviolet light, an electron beam, an ion beam, and X-rays. In this case, the first preset channel, the second preset channel, and the third preset channel can be obtained through the patterning process. Thus, the pad structure of the flexible stimulation electrode can be prepared.

[0024] According to the preparation method, the substrate can be any one of a silicon wafer, a glass wafer, a quartz wafer, a metal sheet, and an alloy sheet. In this case, the silicon wafer, the glass wafer, and the quartz wafer can form the pad structure of the flexible stimulation electrode thereon and have good stability, and the substrate can be removed by mechanical disassembly, reducing the influence of chemical removal on the performance of the pad structure of the flexible stimulation electrode. The metal sheet and the alloy sheet can form the pad structure of the flexible stimulation electrode thereon and can be removed by chemical etching and sacrifice, reducing mechanical damage to the pad structure of the flexible stimulation electrode caused by mechanical removal.

[0025] According to the preparation method, the sacrificial layer can be a 0.5-1.5 μm aluminum film. In this case, the third preset channel can be obtained by patterning the aluminum film in the next preparation process, the fourth preset channel can be obtained by etching the insulating layer through the third preset channel, and the remaining insulating layer that is not etched can be protected.

[0026] According to the first aspect and the second aspect, the pad structure of the flexible stimulation electrode and the preparation method can be provided, wherein the preparation method is compatible with MEMS, has the advantages of mature MEMS process, high repeatability, high yield, and easy batch production, simplifies the preparation process, and can use a simple gold ball welding or conductive adhesive coating process to connect the electrode to the external circuit regardless of single-layer or multi-layer design of the pad structure of the flexible stimulation electrode. The cross-shaped or plum blossom-shaped pad structure can be more reliably connected to the external circuit. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a schematic diagram of the overall flexible stimulation electrode to which the present invention relates;

[0028] Figure 2 is a schematic diagram of the pad array on the flexible stimulation electrode to which the present invention relates;

[0029] Figure 3 is a top view of embodiment 1 of the pad structure to which the present invention relates;

[0030] Figure 4 is a top view of embodiment 2 of the pad structure to which the present invention relates;

[0031] Figure 5 is a top view of embodiment 3 of the pad structure to which the present invention relates;

[0032] Figure 6 is a top view of embodiment 4 of the pad structure to which the present invention relates;

[0033] Figure 7 is a cross-sectional view of the multi-layer pad structure of embodiment 1 to which the present invention relates;

[0034] Figure 8 is a magnified view of the first metal material layer;

[0035] Figure 9 is a magnified view of the second metal material layer;

[0036] Figure 10 is a cross-sectional view of the single-layer pad structure of embodiment 1 to which the present invention relates;

[0037] Figure 11 is a flow chart of the manufacturing process of the embodiment of the multi-layer pad structure to which the present invention relates;

[0038] Figure 12 is a schematic diagram of the application scenario of the pad structure of embodiment 1 and embodiment 3 to which the present invention relates, connected to the feedthrough structure using gold wire bonding or conductive adhesive;

[0039] Figure 13 is a schematic diagram of the application scenario of the pad structure of embodiment 2 and embodiment 4 to which the present invention relates, connected to the feedthrough structure using gold wire bonding or conductive adhesive;

[0040] Figure 14 is a cross-sectional view of the multi-layer pad structure to which the present invention relates, connected to the feedthrough structure using gold wire bonding;

[0041] Figure 15 is a cross-sectional view of the multi-layer pad structure to which the present invention relates, connected to the feedthrough structure and coated with protective adhesive;

[0042] Figure 16is a sectional view of a feedthrough structure connected by gold wire ball bonding using a single layer pad structure according to the present invention;

[0043] Figure 17 is a sectional view of a feedthrough structure connected by gold wire ball bonding using a single layer pad structure according to the present invention; DETAILED DESCRIPTION

[0044] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, the same drawing reference numerals are used for the same elements throughout the several drawings and redundant descriptions are omitted. Also, the drawings are schematic views, and the ratio of the dimensions between the components or the shape of the components and the like can be different from the actual ones. While specific examples of the present invention have been shown and described, it will be understood by those skilled in the art that various changes in form and modifications thereof can be made without departing from the spirit and scope of the invention and its broader aspects, and it is therefore intended that the appended claims encompass all such changes and modifications as fall within the true spirit and scope of the invention. Those skilled in the art will appreciate that the terms used in the present invention are generally intended as "open" terms (e.g., the term "comprising" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "including" should be interpreted as "including but not limited to," and the like). Aspects of the subject matter described herein can be used independently of one another or in combination with any one or more of the other aspects described herein.

[0045] Figure 1 is a schematic view showing a flexible stimulation electrode according to the present invention; Figure 2 is a schematic view showing a pad array on a flexible stimulation electrode according to the present invention; Figure 3 is a top view showing Embodiment 1 of a pad structure according to the present invention; Figure 7 is a sectional view showing a multi-layer pad structure of Embodiment 1 according to the present invention; Figure 10 is a sectional view showing a single layer pad structure of Embodiment 1 according to the present invention.

[0046] As Figure 3 and 7As shown, the first aspect of the present application provides a pad structure 11 of a flexible stimulation electrode 1, which can include an insulating layer 112, a metal material layer 111 and a central via 110. The insulating layer 112 can include a first insulating layer 1121, a second insulating layer 1122 and a third insulating layer 1123, and the metal material layer 111 can include a first metal material layer 1111 and a second metal material layer 1112. The first metal material layer 1111 is formed on the first insulating layer 1121. The second insulating layer 1122 is formed on the first metal material layer 1111 and the first insulating layer 1121 and exposes part of the first metal material layer 1111. The first metal material layer 1111 includes a first adhesive layer 02 and a first conductive layer 01 disposed between two first adhesive layers 02. The second metal material layer 1112 is formed on the first metal material layer 1111 and the second insulating layer 1122. The second metal material layer 1112 includes a second adhesive layer 04 and a second conductive layer 03 between two second adhesive layers 04. The third insulating layer 1123 is formed on the second metal material layer 1112 and the second insulating layer 1122. The first insulating layer 1121, the second insulating layer 1122 and the third insulating layer 1123 are composed of the same material. The central via 110 includes a first via 1101 and a second via 1102. The first via 1101 penetrates and exposes the first insulating layer 1121, the first metal material layer 1111 and the second metal material layer 1112. The second via 1102 penetrates the third insulating layer 1123 and exposes part of the upper surface of the second conductive layer 03.

[0047] In this case, the insulating layer 112 can isolate the metal material layer 111 from the conductive wire of the flexible stimulation electrode 1. The metal material layer 111 can connect the conductive wire of the flexible stimulation electrode 1 and the feedthrough structure 4 to form a circuit conduction. In addition, the central via 110 in the pad structure 11 can enable the pad structure 11 to be connected to the external circuit 5 (see Figures 12 to 17 , described later) using a gold ball bonding or conductive adhesive 12 (see Figures 12 to 17 , described later) process.

[0048] As shown in Figure 7 or 10, in some examples, the pad structure 11 of the flexible stimulation electrode 1 can be a single layer (see Figure 10 ) or a double layer (see Figure 7The metal material layer 111 above and the multi-layer insulating layer 112 are formed. In this case, the single-layer metal material layer 111 forms the pad structure 11 of the flexible stimulating electrode 1, and the manufacturing process is simple, and the electrode pad structure 11 can meet the preparation of a large batch and a lower performance requirement. The double-layer metal material layer 111 forms the pad structure 11 of the flexible stimulating electrode 1, and more wires or leads can be arranged in a three-dimensional network, so that more electrode arrays and pad arrays 10 can be arranged on the same electrode sheet, and the preparation of a higher performance flexible electrode and electrode pad structure 11 can be met. The higher performance flexible stimulating electrode 1 and the pad mechanism can stimulate more nerve cells by increasing the array density.

[0049] As shown in Figure 7 In the present embodiment, the cross section of the first through hole 1101 perpendicular to the extension direction of the first through hole 1101 can be smaller than the cross section of the second through hole 1102 perpendicular to the extension direction of the second through hole 1102, and the cross section of the first through hole 1101 can be parallel to the cross section of the second through hole 1102. In this case, the central through hole 110 formed by the cooperation of the first through hole 1101 and the second through hole 1102 can be more conducive to connecting the pad structure 11 and the external circuit 5 by using the gold ball welding or the conductive glue 12 process. When connected, the feedthrough structure 4 of the external circuit 5 and the metal conductive layer of the pad structure 11 of the flexible stimulating electrode 1 can be connected by using solder or conductive glue 12 in the first through hole 1101, and the solder or conductive glue 12 can be better attached to the metal conductive layer of the pad structure 11 of the flexible stimulating electrode 1 through the second through hole 1102 when connected.

[0050] In some examples, the cross section of the first through hole 1101 perpendicular to the extension direction of the first through hole 1101 can be greater than or equal to the cross section of the second through hole 1102 perpendicular to the extension direction of the second through hole 1102, and the cross section of the first through hole 1101 can be parallel to the cross section of the second through hole 1102. In other examples, the cross section of the first through hole 1101 can not be parallel to the cross section of the second through hole 1102.

[0051] Figure 3 is a top view showing embodiment 1 of the pad structure 11 related to the present application;

[0052] Figure 4 is a top view showing embodiment 2 of the pad structure 11 related to the present application; Figure 5 is a top view showing embodiment 3 of the pad structure 11 related to the present application; Figure 6 is a top view showing embodiment 4 of the pad structure 11 related to the present application.

[0053] As shown in Figures 3 to 6As shown, in this embodiment, optionally, in the central through hole 110, the cross-section of the first through hole 1101 and the cross-section of the second through hole can be circular, square, rectangular, elliptical or a combination thereof, and the combination thereof can be formed by superimposing a circular, square, rectangular or elliptical shape at the center of a cross or plum blossom. In this case, a pad structure 11 of a matching shape can be adaptively selected according to different production requirements. In addition, the combination of a circular, square, rectangular or elliptical shape superimposed at the center of a cross or plum blossom can make the feedthrough structure 4 of the external circuit 5 and the pad of the flexible stimulation electrode 1 more firmly connected.

[0054] In some examples, a combination pattern with a circle, square, rectangle or ellipse superimposed at the center of a cross or plum blossom shape can avoid damage to the pad structure 11 caused by high temperature due to uneven heat dissipation when the feedthrough structure 4 of the external circuit 5 is connected to the pad of the flexible stimulation electrode 1.

[0055] In some examples, the cross-section of the first through hole 1101 and the cross-section of the second through hole can be polygonal or irregular. In this case, a matching shape can be selected to meet the actual preparation requirements of the flexible stimulation electrode 1. For example, an island-shaped or teardrop-shaped pad structure 11 can make the feedthrough structure 4 of the external circuit 5 more densely fixed, thereby reducing the length and number of wires printed on the flexible stimulation electrode 1. In addition, because such a pad has a larger copper foil area, it can enhance the anti-peel strength of the pad.

[0056] like Figure 7 As shown, in this embodiment, optionally, the first insulating layer 1121 can be a polyimide with a thickness of 5 to 6 μm, the second insulating layer 1122 can be a polyimide with a thickness of 1 to 2 μm, and the third insulating layer 1123 can be a polyimide with a thickness of 5 to 6 μm. In this case, a three-dimensional multi-layer pad structure can be formed by multiple insulating layers, and more wires connecting the flexible stimulation electrode 1 and the pad structure 11 of the flexible stimulation electrode 1 can be arranged in the formation of the multi-layer insulating layer. In addition, polyimide has good biocompatibility and mechanical flexibility, which enables the flexible stimulation electrode 1 to be better implanted and used in the human visual area.

[0057] In some examples, the first insulating layer 1121, the second insulating layer 1122, and the third insulating layer 1123 can also be formed of one or a combination of materials such as polyparaxylene, silicone, polydimethylsiloxane, polymethyl methacrylate, polyethylene glycol, or Teflon. For example, the first insulating layer 1121 can be formed of polyimide, the second insulating layer 1122 can be formed of polyimide, and the third insulating layer 1123 can be formed of polyparaxylene. In this case, the transparency, low permeability, and good biocompatibility of the entire electrode and pad structure 11 are improved, and the pad structure 11 is also reduced from high temperature damage to the electrode during the welding process. In addition, other combinations can be used to select materials with different characteristics such as biocompatibility, corrosion resistance, and mechanical flexibility to prepare the flexible stimulation electrode 1 and pad structure 11 according to the biological needs of different parts of the human body for implantation. For example, polyparaxylene has excellent properties such as uniformity, conformality, lack of micropores and defects, and chemical inactivity, and is widely used in biological and biomedical applications.

[0058] In this embodiment, optionally, the area of ​​the first metal material layer 1111 may be smaller than the first insulating layer 1121, and the area of ​​the second metal material layer 1112 may be smaller than the second insulating layer 1122. In this case, multiple first metal material layers 1111 can be formed in the first insulating layer 1121, and multiple second metal material layers 1112 can be formed in the second insulating layer 1122, that is, more pad arrays 10 corresponding to the array of flexible stimulation electrodes 1 are formed.

[0059] Figure 8 It shows Figure 7 A local enlarged view of the first metal material layer 1111 of the multi-layer pad structure; Figure 9 It shows Figure 7 A local enlarged view of the second metal material layer 1112 of the multi-layer pad structure.

[0060] like Figure 8 As shown, in this embodiment, optionally, the first metal material layer 1111 can be a composite material, the first adhesion layer 02 can be a titanium metal layer with a thickness of 30 to 100 nm, and the first conductive layer 01 can be a platinum metal layer with a thickness of 100 to 300 nm. The interface between the first adhesion layer 02 and the first conductive layer 01 can be parallel to the cross section of the first through hole 1101 or the cross section of the second through hole 1102. In this case, the first metal material layer 1111 is formed by sequentially stacking titanium, platinum, and titanium. The titanium layer can increase the adhesion of the first metal material layer 1111 to the various insulating layers, and the platinum layer can serve as the primary conductive medium of the first metal material layer 1111 to connect with the wires or leads of the flexible stimulation electrode 1 and the feedthrough structure 4 of the external circuit 5 to form a conductive circuit.

[0061] In some examples, the first adhesion layer 02 of the first metal material layer 1111 may also be one of platinum, gold, titanium, palladium, iridium, and niobium, or an alloy material.

[0062] In some examples, the first conductive layer 01 of the first metal material layer 1111 may also be one of platinum, gold, titanium, palladium, iridium, and niobium, or an alloy material.

[0063] In other examples, the first metal material layer 1111 may also be made of other non-toxic metals or alloys thereof.

[0064] In some examples, the interface between the first adhesive layer 02 and the first conductive layer 01 may not be parallel to the cross-section of the first through-hole 1101 or the cross-section of the second through-hole 1102. For example, the first conductive layer 01 may be in a laterally tapered trapezoidal shape. In this case, the first conductive layer 01 can be easily connected to the feedthrough structure 4 of the external circuit 5 or the lead (wire) layer of the flexible stimulation electrode 1 according to different manufacturing requirements, thereby improving connection reliability.

[0065] In some examples, the first metal material layer 1111 may not be provided with the first adhesion layer 02. In other words, an insulating layer with good adhesion to the metal material and the first conductive layer 01 may be used to directly form the electrode or pad structure 11. In this case, the manufacturing process can be simplified.

[0066] like Figure 9 As shown, in this embodiment, optionally, the second metal material layer 1112 can be a composite material, the second adhesion layer 04 can be a titanium metal layer with a thickness of 30 to 100 nm, and the second conductive layer 03 can be a platinum metal layer with a thickness of 100 to 300 nm. The interface between the second adhesion layer 04 and the second conductive layer 03 can be parallel to the cross section of the first through hole 1101 or the cross section of the second through hole 1102. In this case, the second metal material layer 1112 is formed by sequentially stacking titanium, platinum, and titanium. The titanium layer can increase the adhesion of the second metal material layer 1112 to the various insulating layers, and the platinum layer can serve as the main conductive medium of the second metal material layer 1112 to connect with the wires or leads of the flexible stimulation electrode 1 and the feedthrough structure 4 of the external circuit 5 to form a conductive circuit.

[0067] In some examples, the second adhesion layer 04 of the second metal material layer 1112 may also be one of platinum, gold, titanium, palladium, iridium, and niobium, or an alloy material.

[0068] In some examples, the second conductive layer 03 of the second metal material layer 1112 may also be one of platinum, gold, titanium, palladium, iridium, and niobium, or an alloy material.

[0069] In other examples, the second metal material layer 1112 may also be made of other non-toxic metals or alloys thereof.

[0070] In some examples, the interface between the second adhesive layer 04 and the second conductive layer 03 can not be parallel to the cross section of the second through hole 1102 or the cross section of the second through hole 1102. For example, the second conductive layer 03 can be a laterally tapered trapezoidal shape, in which case the second conductive layer 03 can be conveniently connected to the feedthrough structure 4 of the external circuit 5 or the lead (wire) layer of the flexible stimulating electrode 1 according to different preparation requirements, improving the connection reliability.

[0071] In some examples, the first metal material layer 1111 can not be provided with the first adhesive layer 02, in other words, the insulating layer with better adhesion to the metal material is directly selected to form the electrode or pad structure 11 with the first conductive layer 01. In this case, the preparation process can be simplified.

[0072] Figure 12 is a schematic diagram showing the application scenario of the pad structure 11 of the embodiments 1 and 3 related to the present application connected to the feedthrough structure 4 by using gold wire ball welding or conductive glue 12; Figure 13 is a schematic diagram showing the application scenario of the pad structure 11 of the embodiments 2 and 4 related to the present application connected to the feedthrough structure 4 by using gold wire ball welding or conductive glue 12; Figure 14 is a cross-sectional view showing the pad structure of the present application connected to the feedthrough structure 4 by using gold wire ball welding;

[0073] Figure 15 is a cross-sectional view showing the pad structure of the present application connected to the feedthrough structure 4 and coated with protective glue 13; Figure 16 is a cross-sectional view showing the pad structure of the present application connected to the feedthrough structure 4 by using gold wire ball welding; Figure 17 is a cross-sectional view showing the pad structure of the present application connected to the feedthrough structure 4 and coated with protective glue 13.

[0074] As shown in Figure 12 , 13 or 14, 16, in the present embodiment, the pad structure 11 can be connected to the feedthrough structure 4 by using gold wire ball welding or conductive glue 12, and the feedthrough structure 4 can be at least one of a feedthrough ceramic, a feedthrough circuit board, and an integrated circuit. In this case, the pad structure 11 of the flexible stimulating electrode 1 is connected to the feedthrough structure 4 of the external circuit 5 by using the gold wire ball welding or conductive glue 12 process, which can enable the electrode array of the flexible stimulating electrode 1 to form a complete sensing circuit through the pad structure 11 (or the pad array 10) and the feedthrough structure 4 of the external circuit 5 to realize the function of the artificial retina. In addition, in the preparation process, the gold wire ball welding or conductive glue 12 process can avoid the complex flip-chip welding process of first making bumps and then welding.

[0075] As shown in Figure 15 and 17 in some examples, the pad structure 11 can be connected with the feedthrough structure 4 by gold wire bonding or conductive glue 12, and then the flexible stimulation electrode 1 is connected with the external circuit 5. After the pad structure 11 is connected with the feedthrough structure 4 by gold wire bonding or conductive glue 12, protective glue 13 can be coated to effectively and reliably protect the connection.

[0076] Figure 11 is a manufacturing process flow chart showing an embodiment of the multi-layer pad structure involved in the present application.

[0077] As shown in Figure 11 the second aspect of the present application provides a preparation method of the pad structure 11 of the flexible stimulation electrode 1, which can include:

[0078] The substrate 3 is prepared, and a first insulating layer 1121 is formed on the substrate 3. The first insulating layer 1121 is processed by a patterning process so that the first insulating layer 1121 has a first preset channel 101 (see (a) of Figure 11 ); a first metal material layer 1111 matching the first preset channel 101 is formed on the first insulating layer 1121 (see (b) of Figure 11 ), the first metal material layer 1111 includes two first adhesive layers 02 and a first conductive layer 01 arranged between the two first adhesive layers 02; a second insulating layer 1122 covering the first insulating layer 1121 and the first metal material layer 1111 is formed on the first insulating layer 1121 and the first metal material layer 1111 (see (c) of Figure 11 ); the second insulating layer 1122 is processed by a patterning process so that the second insulating layer 1122 has a second preset channel 102 (see (d) of Figure 11 ); a second metal material layer 1112 matching the second preset channel 102 is formed on the second insulating layer 1122 (see (e) of Figure 11 ), the second metal material layer 1112 includes two second adhesive layers 04 and a second conductive layer 03 arranged between the two second adhesive layers 04; a third insulating layer 1123 covering the second insulating layer 1122 and the second metal material layer 1112 is formed on the second metal material layer 1112 (see (f) of Figure 11 ); a sacrificial layer 2 is formed on the third insulating layer 1123 (see (g) of Figure 11 ) and processed by a patterning process so that the sacrificial layer 2 has a third preset channel 103 (see (h) of Figure 11 ); the first insulating layer 1121, the second insulating layer 1122, and the third insulating layer 1123 are processed based on the third preset channel 103 to form a fourth preset channel 104 (seeFigure 11 In (i)); removing the sacrificial layer 2 (see Figure 11 In (j)); removing part of the second adhesive layer 04 based on the fourth preset channel 104 to expose part of the upper surface of the second conductive layer 03 (see Figure 11 In (k)); removing the substrate 3 to form the central through hole 110 (see Figures 11 to 17 In (l)), the central through hole 110 includes a first through hole 1101 and a second through hole 1102, the first through hole 1101 penetrates and exposes the first insulating layer 1121, the first metal material layer 1111, and the second metal material layer 1112, and the second through hole 1102 penetrates the third insulating layer 1123 and exposes part of the upper surface of the second conductive layer 03.

[0079] In this case, the multilayer pad structure 11 obtained by the preparation method of the pad structure 11 of the flexible stimulation electrode 1 can directly connect the first metal material layer 1111 with the second metal material layer 1112, avoiding the dependence on the deposited material for constructing mechanical structures or electronic components when using complex electroplating processes. In addition, the preparation method is compatible with MEMS, which can take advantage of the mature MEMS process, high repeatability, high yield, and easy batch production.

[0080] In some examples, the process of preparing the substrate 3 can also include cleaning and plasma treatment processes. In some examples, the cleaning process can use an FSI cleaning machine or an RCA cleaning machine.

[0081] In some examples, the process of forming the first insulating layer 1121, the second insulating layer 1122, and the third insulating layer 1123 can also include processes such as spin coating, pre-baking, and vacuum nitrogen baking and curing.

[0082] In some examples, the process of forming the first preset channel 101, the second preset channel 102, the third preset channel 103, and the fourth preset channel 104 can also include processes such as spin coating photoresist, exposure, etching, and stripping.

[0083] In some examples, the process of forming the first metal material layer 1111 and the second metal material layer 1112 can also include processes such as spin coating photoresist, exposure, plasma treatment of the surface, sputtering of a gold layer, stripping of the surface resist, and metal on resist, and titanium layer etching.

[0084] In the embodiment, optionally, the cross section of the first through hole 1101 perpendicular to the extending direction of the first through hole 1101 can be smaller than the cross section of the second through hole 1102 perpendicular to the extending direction of the second through hole 1102, and the cross section of the first through hole 1101 can be parallel to the cross section of the second through hole 1102; the cross section of the first through hole 1101 and the cross section of the second through hole 1102 can be one of a circle, a square, a rectangle, an ellipse or a combined pattern, and the combined pattern can be formed by superimposing one of a circle, a square, a rectangle or an ellipse at the center position of a cross or a plum blossom pattern.

[0085] In this case, the central through hole 110 formed by the cooperation of the first through hole 1101 and the second through hole 1102 can be more conducive to connecting the pad structure 11 and the external circuit 5 by using the gold ball welding or conductive glue 12 process, and when connected, the solder or conductive glue 12 can be used in the first through hole 1101 to connect the feedthrough structure 4 of the external circuit 5 and the metal conductive layer of the pad structure 11 of the flexible stimulating electrode 1, and when connected, the solder or conductive glue 12 can be better attached to the metal conductive layer of the pad structure 11 of the flexible stimulating electrode 1 through the second through hole 1102. In addition, the pad structure 11 manufactured in different matching shapes can be adaptively selected according to different production needs, and the combined pattern of the circle, square, rectangle or ellipse superimposed at the center position of the cross or plum blossom pattern can make the connection of the feedthrough structure 4 of the external circuit 5 and the pad of the flexible stimulating electrode 1 more firm.

[0086] In the embodiment, optionally, the first preset channel 101 can be one of a circular, square, rectangular, elliptical or combined pattern ring, the combined pattern is formed by superimposing one of a circle, a square, a rectangle or an ellipse at the center position of a cross or a plum blossom pattern; the second preset channel 102 can be one of a circular, square, rectangular, elliptical or combined pattern ring, the combined pattern is formed by superimposing one of a circle, a square, a rectangle or an ellipse at the center position of a cross or a plum blossom pattern, and the area of the second preset channel 102 is smaller than that of the first preset channel 101; the third preset channel 103 can be one of a circular, square, rectangular, elliptical or combined pattern, the combined pattern is formed by superimposing one of a circle, a square, a rectangle or an ellipse at the center position of a cross or a plum blossom pattern; the fourth preset channel 104 can be one of a circular, square, rectangular, elliptical or combined pattern, the combined pattern is formed by superimposing one of a circle, a square, a rectangle or an ellipse at the center position of a cross or a plum blossom pattern.

[0087] In this case, the first metal material layer 1111 in a ring shape can be formed through the first preset channel 101, the second metal material layer 1112 in a ring shape can be formed through the second preset channel 102, the fourth preset channel 104 can be formed through the third preset channel 103, and the fourth preset channel 104 can be formed into the final central through hole 110 by removing the substrate 3, the sacrificial layer 2, and the second adhesive layer 04 on the upper surface of the partial second metal material layer 1112, so that the pad structure 11 of the flexible stimulation electrode 1 can be prepared, and the pad structure 11 can be connected to the external circuit 5 through the central through hole 110 in the pad structure 11 by using gold ball welding or conductive glue 12 coating process.

[0088] In the embodiment, optionally, the patterning process can be a process of using a photoresist to develop and expose a predetermined pattern by irradiation or radiation of any one of ultraviolet light, an electron beam, an ion beam, and X-rays. In this case, the first preset channel 101, the second preset channel 102, and the third preset channel 103 with accurate patterns can be obtained through the patterning process, so that the pad structure 11 of the flexible stimulation electrode 1 can be prepared.

[0089] In the embodiment, optionally, the substrate 3 can be any one of a silicon wafer, a glass wafer, a quartz wafer, a metal, and an alloy sheet. In this case, the silicon wafer, the glass wafer, and the quartz wafer can form the pad structure 11 of the flexible stimulation electrode 1 thereon and have good stability, and can be removed by mechanical disassembly, reducing the influence of chemical removal on the performance of the pad structure 11 of the flexible stimulation electrode 1, and the metal and alloy sheet can form the pad structure 11 of the flexible stimulation electrode 1 thereon and can be removed by chemical etching and sacrificial method, reducing the mechanical damage to the pad structure 11 of the flexible stimulation electrode 1 caused by mechanical removal.

[0090] In the embodiment, optionally, the sacrificial layer 2 can be a 0.5-1.5 μm aluminum film. In this case, by forming the aluminum film sacrificial layer 2, the third preset channel 103 can be obtained by patterning the aluminum film in the next preparation process, so that the fourth preset channel 104 can be obtained by etching the insulating layer through the third preset channel 103, and the remaining insulating layer not etched can be protected.

[0091] In other examples, the sacrificial layer 2 can be one of 0.5-1.5 μm aluminum, chromium, titanium, and other metals or an alloy thereof.

[0092] The following provides an embodiment of a specific manufacturing process in combination with the foregoing Figure 11To further illustrate the pad structure 11 of the flexible stimulation electrode 1 and the method for manufacturing the same according to the present application, wherein the insulating layer is selected as polyimide, the sacrificial layer 2 (hard mask) is selected as aluminum film, and the metal material layer 111 is selected as titanium-platinum-titanium structure:

[0093] 1. Select a silicon wafer as the substrate 3, remove the natural oxide layer on the surface by using FSI cleaning, then further clean by using RCA, dry by using a spin-dryer, and then treat the surface by using plasma for 2-3 min, spin-coat a first layer of polyimide (3000 rpm, 35 s) to a thickness of about 5-6 μm, pre-bake at 150°C for 3 min, and then bake in a vacuum nitrogen oven at 350°C for 0.5-1 h to solidify. (See Figure 11 (a)

[0094] 2. Apply a layer of negative photoresist or a double layer of positive photoresist and negative photoresist on the first layer of polyimide, and after exposure and development, obtain a pattern, which is different according to different photoetching plates. Then treat the surface by using plasma, and then sputter a composite metal layer of 30-100 nm titanium, 100-300 nm platinum and 30-100 nm titanium, remove the surface photoresist and the sputtered metal on the photoresist by peeling, and leave the composite metal layer as the first metal material layer 1111. (See Figure 11 (b)

[0095] 3. Spin-coat a second layer of insulating layer polyimide (5000 rpm, 35 s) to a thickness of about 1-2 μm, pre-bake at 150°C for 3 min, and then bake in a vacuum nitrogen oven at 350°C for 0.5-1 h to solidify. (See Figure 11 (c)

[0096] 4. Spin-coat a layer of positive photoresist, and after exposure and development, etch the polyimide by using RIE equipment, and then remove the photoresist by using a photoresist remover to form a channel. (See Figure 11 (d)

[0097] 5. Apply a layer of negative photoresist or a double layer of positive photoresist and negative photoresist, and after exposure and development, treat the surface by using plasma. Then sputter a composite metal layer of 30-100 nm titanium, 100-300 nm platinum and 30-100 nm titanium, remove the surface photoresist and the sputtered metal on the photoresist by peeling, and leave the composite metal layer as the second metal material layer 1112. (See Figure 11 (e)

[0098] 6. Spin-coat a third layer of insulating layer polyimide (3000 rpm, 35 s) to a thickness of about 5-6 μm, pre-bake at 150°C for 3 min, and then bake in a vacuum nitrogen oven at 350°C for 0.5-1 h to solidify. (See Figure 11 (f)

[0099] 7. After pre-treating the third layer of polyimide by using a plasma photoresist remover, sputter or evaporate a layer of hard mask (i.e. the sacrificial layer 2) such as 1 μm aluminum. (SeeFigure 11 Figure 6 (g)

[0100] 8. Spin the positive photoresist, after exposure and development, etch in aluminum etchant to get the patterned hard mask. (See Figure 7 (h) Figure 11 Figure 6 (h)

[0101] 9. Etch the polyimide using RIE to expose the pad metal and via. (See Figure 8 (i) Figure 11 Figure 6 (i)

[0102] 10. Etch the hard mask aluminum using aluminum etchant to get the electrode pad. (See Figure 9 (j) Figure 11 Figure 6 (j)

[0103] 11. Put the electrode into HF solution (hydrofluoric acid) to etch for 30s to etch away the titanium layer on the pad metal surface. (See Figure 10 (k) Figure 11 Figure 6 (k)

[0104] 12. Use a special method to take the electrode off the substrate to get the bare electrode. (See Figure 11 (1) Figures 12 to 14 Figure 6 (1)

[0105] 13. Use a gold ball bonder to bond the gold ball through the via to the pad on the feedthrough ceramic. (See Figure 12 (m) Figure 16 and Figure 13 (m). Figure 15 14. After all the pads are bonded, drop the protective glue 13. (See Figure 14 (n)

[0106] , Figure 17 ​

[0107] According to the first and second aspects of the present application, a pad structure of a flexible stimulation electrode and a preparation method thereof are provided, wherein the preparation method is compatible with MEMS, and the advantages of mature MEMS process, high repeatability, high yield, and easy mass production are exerted, while the preparation process is simplified, and the pad structure of the flexible stimulation electrode prepared by the present application can be connected to an external circuit by simple gold ball bonding or conductive glue coating process, and the cross-shaped or plum blossom-shaped combined pad structure can be more reliably connected to the external circuit.

[0108] According to the first and second aspects of the present application, a pad structure of a flexible stimulation electrode and a preparation method thereof are provided, wherein the preparation method is compatible with MEMS, and the advantages of mature MEMS process, high repeatability, high yield, and easy mass production are exerted, while the preparation process is simplified, and the pad structure of the flexible stimulation electrode prepared by the present application can be connected to an external circuit by simple gold ball bonding or conductive glue coating process, and the cross-shaped or plum blossom-shaped combined pad structure can be more reliably connected to the external circuit. ​​

[0109] Preferred examples of the present application are described herein, including the best mode known to the inventors for practicing the application. Variations of those preferred examples will become apparent to those of ordinary skill in the art upon reading the foregoing description. It is intended that all such variations be included within the scope of the present application. It is intended that the present application be practiced by those of ordinary skill in the art having the benefit of this disclosure. Accordingly, proper and suitable modification and equivalents of the described embodiments are intended to be covered by the following claims.

[0110] Although the present application has been described above with reference to particular and preferred embodiments, it is apparent that numerous other variations and modifications can be made to the present application without departing from the spirit and scope of the application. Accordingly, the present application is not limited to the embodiments described above, but includes all modifications and equivalents within the scope of the following claims.

Claims

1. A pad structure of a flexible stimulation electrode, characterized in that, comprising: a first insulating layer, a first metal material layer, a second insulating layer, a second metal material layer, a third insulating layer, and a central via, the first metal material layer is formed on the first insulating layer; the second insulating layer is formed on the first metal material layer and the first insulating layer and exposes part of the first metal material layer, the first metal material layer comprises two first adhesive layers and a first conductive layer arranged between the two first adhesive layers; the second metal material layer is formed on the first metal material layer and the second insulating layer, the second metal material layer is connected with the first metal material layer, the second metal material layer comprises two second adhesive layers and a second conductive layer arranged between the two second adhesive layers; the third insulating layer is formed on the second metal material layer and the second insulating layer; the first insulating layer, the second insulating layer, and the third insulating layer are composed of the same material; the central via comprises a first via and a second via, the first via penetrates and exposes the first insulating layer, the first metal material layer, and the second metal material layer, the second via penetrates the third insulating layer and exposes part of the upper surface of the second conductive layer, so that the pad structure is connected with a feedthrough structure using a gold ball bonding process or a conductive adhesive coating process. 2.The pad structure according to claim 1, characterized in that, a cross section of the first via perpendicular to the extension direction of the first via is smaller than a cross section of the second via perpendicular to the extension direction of the second via, and the cross section of the first via is parallel to the cross section of the second via. 3.The pad structure according to claim 1, characterized in that, the cross section of the first via and the cross section of the second via are one of circular, square, rectangular, elliptical, or a combination pattern formed by superimposing one of circular, square, rectangular, or elliptical on a cross center or a plum blossom center position. 4.The pad structure according to claim 1, characterized in that, the first insulating layer is polyimide with a thickness of 5-6μm, the second insulating layer is polyimide with a thickness of 1-2μm, and the third insulating layer is polyimide with a thickness of 5-6μm. 5.The pad structure according to claim 1, characterized in that, the area of the first metal material layer is smaller than the first insulating layer, and the area of the second metal material layer is smaller than the second insulating layer. 6.The pad structure according to claim 1 or 2, characterized in that, the first metal material layer is a composite material, the first adhesive layer is a titanium metal layer with a thickness of 30-100nm, the first conductive layer is a platinum metal layer with a thickness of 100-300nm, and the interface of the first adhesive layer and the first conductive layer is parallel to the cross section of the first via or the cross section of the second via. 7.The pad structure according to claim 1 or 2, characterized in that, The second metal material layer is a composite material, the second adhesion layer is a titanium metal layer with a thickness of 30-100 nm, and the second conductive layer is a platinum metal layer with a thickness of 100-300 nm. The interface between the second adhesion layer and the second conductive layer is parallel to the cross section of the first through hole or the cross section of the second through hole.

8. The pad structure of claim 1, wherein, The pad structure is connected to a feedthrough structure by gold wire bonding or drop-coated conductive adhesive, and the feedthrough structure is at least one of a feedthrough ceramic substrate, a feedthrough circuit board, and an integrated circuit.

9. A method of manufacturing a pad structure of a flexible stimulation electrode, characterized by Comprise: A substrate is prepared, and a first insulating layer is formed on the substrate. The first insulating layer is processed by a patterning process to have a first preset channel. A first metal material layer matching the first preset channel is formed on the first insulating layer. The first metal material layer comprises two first adhesion layers and a first conductive layer disposed between the two first adhesion layers. A second insulating layer covering the first insulating layer and the first metal material layer is formed on the first insulating layer and the first metal material layer. The second insulating layer is processed by a patterning process to have a second preset channel. A second metal material layer matching the second preset channel is formed on the second insulating layer. The second metal material layer comprises two second adhesion layers and a second conductive layer disposed between the two second adhesion layers. The second metal material layer is connected to the first metal material layer. A third insulating layer covering the second insulating layer and the second metal material layer is formed on the second metal material layer. A sacrificial layer is formed on the third insulating layer and processed by a patterning process to have a third preset channel. The first insulating layer, the second insulating layer, and the third insulating layer are processed based on the third preset channel to form a fourth preset channel. The sacrificial layer is removed. Part of the second adhesion layer is removed based on the fourth preset channel to expose part of the upper surface of part of the second conductive layer. The substrate is removed to form a central through hole. The central through hole comprises a first through hole and a second through hole. The first through hole penetrates and exposes the first insulating layer, the first metal material layer, and the second metal material layer. The second through hole penetrates the third insulating layer and exposes part of the upper surface of part of the second conductive layer, so that the pad structure is connected to a feedthrough structure by a gold wire bonding process or a drop-coated conductive adhesive process.

10. The preparation method of claim 9, wherein The cross section of the first through hole perpendicular to the extension direction of the first through hole is smaller than the cross section of the second through hole perpendicular to the extension direction of the second through hole, and the cross section of the first through hole is parallel to the cross section of the second through hole. The cross section of the first through hole and the cross section of the second through hole are one of circular, square, rectangular, elliptical, or a combination pattern formed by superimposing a cross-shaped center or a plum blossom-shaped center on one of a circular, square, rectangular, or elliptical shape.

11. The method of claim 9, wherein, a cross section of the first predetermined channel orthogonal to a direction of extension of the first predetermined channel is one of a circle, a square, a rectangle, an ellipse, or a combined pattern formed by superimposing one of a circle, a square, a rectangle, or an ellipse at a center of a cross or a plum blossom pattern; a cross section of the second predetermined channel is one of a circle, a square, a rectangle, an ellipse, or a combined pattern formed by superimposing one of a circle, a square, a rectangle, or an ellipse at a center of a cross or a plum blossom pattern, and the second predetermined channel has a smaller area than the first predetermined channel; a cross section of the third predetermined channel is one of a circle, a square, a rectangle, an ellipse, or a combined pattern formed by superimposing one of a circle, a square, a rectangle, or an ellipse at a center of a cross or a plum blossom pattern; a cross section of the fourth predetermined channel is one of a circle, a square, a rectangle, an ellipse, or a combined pattern formed by superimposing one of a circle, a square, a rectangle, or an ellipse at a center of a cross or a plum blossom pattern.

12. The method of claim 9, wherein, the patterning process is a photoresist process using any one of ultraviolet light, an electron beam, an ion beam, or X-rays.

13. The method of claim 9, wherein, the substrate is any one of a silicon wafer, a glass wafer, a quartz wafer, a metal, or an alloy.

14. The method of claim 9, wherein, the sacrificial layer is a metal aluminum film having a thickness of 0.5 to 1.5 μm.

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