An easily releasable ultra-thin flexible neural electrode array and preparation method thereof

Abstract

The present invention discloses an ultra-thin flexible neural electrode array that is easy to release and a preparation method thereof. The present invention utilizes spin-coated sodium polystyrene sulfonate PSS as a release sacrificial layer, and utilizes the strong hydrophilicity of PSS to make it easier to detach from the substrate when releasing the device. The release process described does not involve harmful reagents such as strong acids and strong bases. Before the release operation, it is compatible with traditional micro-nano processing technology, including compatible processing steps such as lithography, etching, and deposition. By adding release materials in specific areas, the release time of the ultra-thin flexible electrode can be greatly accelerated to protect the integrity of the flexible electrode. The present invention is easy to operate and can easily release ultra-thin flexible neural electrode arrays of different sizes.

Description

Technical Field

[0001] The present invention belongs to the fields of medical equipment, biomedical engineering and micro-nano processing technology, and in particular, relates to an easily releasable ultra-thin flexible neural electrode array and a preparation method thereof. Background Art

[0002] In recent years, with the development of neural interface technology, implantable devices for human body have been designed and manufactured. They have been applied in many fields, especially in medicine, and are seeking wide applications in industry, military and consumer fields. Based on micro-nano processing technology, the current research focuses on making multiple electrodes on flexible materials through photolithography, and then etching the flexible materials into extremely fine lines through micro-processing to make multi-channel electrodes on extremely small electrode sizes. However, this kind of flexible material is generally made on rigid substrates such as silicon wafers or glass wafers. These flexible materials are very easy to damage, resulting in many problems when released from the substrate.

[0003] In 2016, Xiaoyang Kang et al. published an article titled Sputtered iridium oxide modified flexible parylene microelectrodes array for electrical recording and stimulation of muscles in the journal Sensors and Actuators B 225 (2016) 267-78. The article disclosed a method for making a flexible electrode array based on parylene. This method mainly prepares iridium oxide electrodes by sputtering metal and photolithography, but hydrofluoric acid is used to peel off the substrate, and the preparation process is relatively complicated.

[0004] In 2018, Giuseppe Schiavone et al. published an article titled Long-term functionality of a soft electrode array for epidural spinal cord stimulation in a minipig model at the IEEE Engineering in Medicine and Biology Society Conference. The article produced an implant with an 8-electrode array by embedding a gold film wire between two layers of silicone rubber. Although the release process of the neural electrode is also relatively simple, this method is suitable for the release process of relatively thick flexible devices.

[0005] In summary, although the preparation and release methods of soft electrodes have been studied to a certain extent, most of them are limited to the use of harmful reagents such as strong acids and strong bases, or are only suitable for the release of thicker flexible electrodes, without considering the problem of ultra-thin flexible electrode substrate peeling and packaging. Summary of the invention

[0006] In view of the research needs of ultra-thin flexible neural electrode arrays and the defects in the prior art, the purpose of the present invention is to provide an easily releasable ultra-thin flexible neural electrode array and a preparation method thereof. The ultra-thin refers to the thickness of the flexible material being less than 10 microns, which can conformally fit the neural tissue. Flexible materials include but are not limited to parylene, silicone rubber, polyimide and other materials commonly used in the field of flexible electronics. The technical solution of the present invention is specifically described as follows.

[0007] A method for preparing an easily releasable ultrathin flexible neural electrode array comprises the following steps:

[0008] (1) Laminating a polyethylene terephthalate (PET) silicone protective film on a silicon wafer, flattening it with a laminating machine, and squeezing out possible bubbles; wherein the polyethylene terephthalate (PET) silicone protective film consists of a PET film layer and a silicone layer, the thickness of the PET film layer is 5-100 microns, and the thickness of the silicone layer is 5-200 microns;

[0009] (2) Using laser to cut the PET silicone protective film, the cutting route is along the edge of the silicon wafer, the equivalent diameter of the cutting route is smaller than the silicon wafer, and the ratio of the cutting diameter to the silicon wafer diameter ranges from 0.05:1 to 0.99:1;

[0010] (3) Remove the PET silicone protective film in the middle area of ​​the cut substrate, and spin-coat a layer of sodium polystyrene sulfonate (PSS) on the exposed silicon wafer as the release layer material for the ultra-thin flexible neural electrode array;

[0011] (4) After spin coating, remove the PET silicone protective film on the silicon wafer and place the silicon wafer on a hot plate or in an oven.

[0012] Drying is performed to obtain a silicon wafer with a middle region covered with a sodium polystyrene sulfonate PSS layer and an edge region exposed;

[0013] (5) Fabrication of ultra-thin flexible neural electrode arrays in the central area of ​​the silicon wafer using micro-nano processing technology;

[0014] (6) The silicon wafer with the ultra-thin flexible neural electrode array prepared in step (5) is placed in clean water, and the sodium polystyrene sulfonate PSS quickly dissolves in the water, and the ultra-thin flexible neural electrode array is quickly released from the silicon wafer, or the connector of the packaged electrode is placed in clean water for release, thereby obtaining an ultra-thin flexible neural electrode array.

[0015] In the present invention, in step (3), the spin coating liquid is a polystyrene sulfonate sodium PSS aqueous solution with a concentration of 2-50wt%, and the spin coating speed ranges from 200 to 6000 rpm.

[0016] In the present invention, in step (4), the drying temperature is 50-250° C., and the drying time is 2-20 hours.

[0017] In the present invention, step (4) is replaced by the following step: after the spin coating is completed, the PET silicone protective film on the silicon wafer is retained, the whole is placed on a hot plate or in an oven for drying, and then the PET silicone protective film on the silicon wafer is removed.

[0018] In the present invention, the drying temperature is 50-150° C. and the drying time is 2-20 hours.

[0019] In the present invention, in step (5), the specific steps of preparing an ultra-thin flexible neural electrode array in the central area of ​​a silicon wafer are as follows:

[0020] A layer of Parylene-C is deposited on the silicon wafer using chemical vapor deposition;

[0021] Spray positive photoresist and pattern it, sputter or evaporate the electrode conductive layer, use lift-off process to remove the photoresist, and the metal layer forms the conductive structure of the electrode;

[0022] The second layer of Parylene-C was deposited by chemical vapor deposition again, and then the positive resist was spun and patterned. The Parylene-C was etched by reactive ion etching to expose the electrode points and etch the electrode outline to form the covering layer of the microelectrode array. Finally, the residual photoresist was cleaned off.

[0023] In the present invention, the steps Replace with the following steps: use chemical vapor deposition to deposit the second layer of Parylene-C again, then spin positive resist and pattern it, clean the residual photoresist and directly package the connector of the electrode, and then form the outer contour of the electrode by laser cutting.

[0024] The present invention further provides an ultra-thin flexible neural electrode array prepared by the above preparation method.

[0025] In the present invention, the easy release means that the ultra-thin flexible neural electrode array is easily peeled off from a substrate such as a silicon wafer or a glass wafer to obtain an independent ultra-thin flexible neural electrode array.

[0026] In the present invention, the PSS around the edge of the silicon wafer is removed to prevent the device from falling off due to the inability of Parylene and PSS to be tightly connected during the preparation process. It also prevents the relevant chemical reagents from entering the surface of the silicon wafer after the Parylene-C at the edge is broken, causing the device to peel off or be damaged.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] In the present invention, by adding release materials in specific areas, the release time of the ultra-thin flexible electrode can be greatly accelerated, and the integrity of the ultra-thin flexible electrode can be protected.

[0029] The present invention uses spin-coated PSS as a release sacrificial layer, and utilizes the strong hydrophilicity of PSS to make it easier to detach from the substrate when releasing the device. The release process does not involve harmful reagents such as strong acids and strong bases. The ultra-thin flexible device does not receive additional mechanical stress and is not easily damaged.

[0030] The present invention is compatible with conventional micro-nano processing techniques before the release operation, including compatible processing steps such as photolithography, etching, and deposition.

[0031] The present invention is easy to operate and can easily release ultra-thin flexible neural electrode arrays of different sizes. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the key layout design of the easily releasable ultra-thin flexible neural electrode array in the embodiment of the present invention.

[0033] Numbers in the figure: 1-silicon wafer, 2-laser cutting area (PSS layer), 3-ultra-thin flexible neural electrode array. DETAILED DESCRIPTION

[0034] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several variations and improvements may be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0035] Example 1

[0036] This embodiment provides a method for preparing an ultra-thin and flexible neural electrode array that is easily releasable based on Parylene-C. The specific preparation process is as follows:

[0037] (1) Apply a polyethylene terephthalate (PET) silicone protective film to the silicon wafer and flatten it with a laminator to squeeze out any bubbles. The entire silicon wafer area is applied, such as Figure 1The area indicated by the middle number 1. The thickness of the PET film is 25 microns, and the thickness of the silica gel is 50 microns.

[0038] (2) Use laser to cut the PET silicone protective film. The cutting route is along the edge of the silicon wafer. The cut area is as follows: Figure 1 The area indicated by number 2. The equivalent diameter of the cutting route is smaller than that of the silicon wafer, and the ratio of the cutting diameter to the silicon wafer diameter is 0.9:1.

[0039] (3) Remove the cut PET silicone protective film and spin coat a layer of sodium polystyrene sulfonate (PSS) on the silicon wafer as the release layer material of the ultra-thin flexible neural electrode array at a spin coating speed of 4000 rpm.

[0040] (4) Sodium polystyrene sulfonate PSS can be used in aqueous solution, with the mass ratio of the solution being 5wt%.

[0041] (5) After the spin coating is completed, you can keep the PET silicone protective film on the silicon wafer and place the whole on a hot plate or in an oven for drying. The drying temperature range is 85°C. After the drying is completed, remove the PET silicone protective film on the silicon wafer.

[0042] (6) At this point, there was no sodium polystyrene sulfonate (PSS) in the area near the edge of the silicon wafer, while the central area, where the ultrathin flexible neural electrode array was prepared in the next step, successfully retained sodium polystyrene sulfonate (PSS).

[0043] (7) A layer of Parylene-C with a thickness of 2 μm is further deposited on the silicon wafer by chemical vapor deposition.

[0044] (8) Sputter the positive photoresist and pattern it, sputter or evaporate the electrode conductive layer, use the lift-off process to remove the photoresist, and the metal layer forms the conductive structure of the electrode. The area where the conductive structure of the electrode is located is as follows Figure 1 The area indicated by number 3.

[0045] (9) The second layer of Parylene-C is deposited by chemical vapor deposition again, with a thickness of 2 μm. Then, a positive resist is applied and patterned, and Parylene-C is etched by reactive ion etching to expose the electrode points, forming the covering layer of the microelectrode array.

[0046] (10) After cleaning the residual photoresist, the connector of the electrode is directly encapsulated. The outer contour of the electrode is then completed by laser cutting, and then the silicon wafer is placed in clean water for release. The release time is 2 minutes.

[0047] Example 2

[0048] This embodiment provides a method for preparing an ultra-thin and flexible neural electrode array that is easily releasable based on Parylene-C. The specific preparation process is as follows:

[0049] (1) Apply a polyethylene terephthalate (PET) silicone protective film to the silicon wafer and flatten it with a laminator to squeeze out any bubbles. The entire silicon wafer area is applied, such as Figure 1 The area indicated by the middle number 1. The thickness of the PET film is 50 microns, and the thickness of the silica gel is 100 microns.

[0050] (2) Use laser to cut the PET silicone protective film. The cutting route is along the edge of the silicon wafer. The cut area is as follows: Figure 1 The area indicated by number 2. The equivalent diameter of the cutting route is smaller than that of the silicon wafer, and the ratio of the cutting diameter to the silicon wafer diameter is 0.8:1.

[0051] (3) Remove the cut PET silicone protective film and spin coat a layer of sodium polystyrene sulfonate (PSS) on the silicon wafer as the release layer material of the ultra-thin flexible neural electrode array at a spin coating speed of 2000 rpm.

[0052] (4) Sodium polystyrene sulfonate PSS can be used in aqueous solution, with the mass ratio of the solution being 5wt%.

[0053] (5) After spin coating, remove the PET silicone protective film on the silicon wafer and place the silicon wafer on a hot plate or in an oven.

[0054] The silicon wafer was dried to obtain a silicon wafer with a middle region covered with a sodium polystyrene sulfonate (PSS) layer and an edge region exposed. The drying temperature was 125°C.

[0055] (6) At this point, there was no sodium polystyrene sulfonate (PSS) in the area near the edge of the silicon wafer, while the central area, where the ultrathin flexible neural electrode array was prepared in the next step, successfully retained sodium polystyrene sulfonate (PSS).

[0056] (7) A layer of Parylene-C with a thickness of 1.5 μm is deposited on the silicon wafer using chemical vapor deposition.

[0057] (8) Sputter the positive photoresist and pattern it, sputter or evaporate the electrode conductive layer, use the lift-off process to remove the photoresist, and the metal layer forms the conductive structure of the electrode. The area where the conductive structure of the electrode is located is as follows Figure 1 The area indicated by number 3.

[0058] (9) The second layer of Parylene-C is deposited by chemical vapor deposition again, with a thickness of 1.5 μm. Then, a positive resist is applied and patterned, and Parylene-C is etched by reactive ion etching to expose the electrode points, forming the covering layer of the microelectrode array.

[0059] (10) After cleaning the residual photoresist, the connector of the electrode is directly encapsulated. The outer contour of the electrode is then completed by laser cutting, and then the silicon wafer is placed in clean water for release. The release time is 3 minutes.

[0060] In summary, the present invention uses spin-coated PSS as a release sacrificial layer to shorten the release time of the electrode. The ultra-thin flexible device does not receive additional mechanical stress, protecting the integrity of the ultra-thin flexible electrode. Removing PSS from the edge of the silicon wafer prevents accidental shedding or damage of Parylene during the preparation process.

[0061] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing an easily releasable ultra-thin flexible neural electrode array, characterized in that: The following steps are involved: (1) Laminating a polyethylene terephthalate (PET) silicone protective film on a silicon wafer, flattening it with a laminating machine, and squeezing out possible bubbles; wherein the polyethylene terephthalate (PET) silicone protective film consists of a PET film layer and a silicone layer, the thickness of the PET film layer is 5-100 microns, and the thickness of the silicone layer is 5-200 microns; (2) Using laser to cut the PET silicone protective film, the cutting route is along the edge of the silicon wafer, the equivalent diameter of the cutting route is smaller than the silicon wafer, and the ratio of the cutting diameter to the silicon wafer diameter ranges from 0.05:1 to 0.99:1; (3) Remove the PET silicone protective film in the middle area of ​​the cut substrate, and spin-coat a layer of sodium polystyrene sulfonate (PSS) on the exposed silicon wafer as the release layer material for the ultra-thin flexible neural electrode array; (4) After the spin coating is completed, the PET silicone protective film on the silicon wafer is removed, and the silicon wafer is placed on a hot plate or in an oven for drying to obtain a silicon wafer with a polystyrene sulfonate (PSS) layer covering the middle area and a bare edge area; (5) Fabrication of ultra-thin flexible neural electrode arrays in the central area of ​​the silicon wafer using micro-nano processing technology; (6) The silicon wafer with the ultra-thin flexible neural electrode array prepared in step (5) is placed in clean water, and the sodium polystyrene sulfonate PSS is quickly dissolved in the water, and the ultra-thin flexible neural electrode array is quickly released from the silicon wafer, or the connector of the encapsulated electrode is placed in clean water for release to obtain an ultra-thin flexible neural electrode array; wherein: In step (5), the specific steps of preparing the ultra-thin flexible neural electrode array in the central area of ​​the silicon wafer are as follows: ①Use chemical vapor deposition to continue depositing a layer of Parylene-C on the silicon wafer; ② Spray the positive photoresist and pattern it, sputter or evaporate the electrode conductive layer, use the lift-off process to remove the photoresist, and the metal layer forms the conductive structure of the electrode; ③ Use chemical vapor deposition to deposit the second layer of Parylene-C again, then spin the positive resist and pattern it, use reactive ion etching of Parylene-C to expose the electrode points, etch the electrode outline to form the covering layer of the microelectrode array, and finally clean off the residual photoresist.

2. The preparation method according to claim 1, characterized in that: In step (3), the spin coating liquid is a polystyrene sulfonate (PSS) aqueous solution with a concentration of 2-50 wt %, and the spin coating speed ranges from 200 to 6000 rpm.

3. The preparation method according to claim 1, characterized in that: In step (4), the drying temperature is 50-250° C. and the drying time is 2-20 hours.

4. The preparation method according to claim 1, characterized in that: Step (4) is replaced by the following steps: After the spin coating is completed, first keep the PET silicone protective film on the silicon wafer, place the whole on a hot plate or in an oven for drying, and then remove the PET silicone protective film on the silicon wafer.

5. The preparation method according to claim 4, characterized in that: The drying temperature is 50-150°C and the drying time is 2-20 hours.

6. The preparation method according to claim 1, characterized in that: Step ③ is replaced by the following steps: the second layer of Parylene-C is deposited by chemical vapor deposition again, and then the positive photoresist is spun and patterned, and the connector of the electrode is directly packaged after the residual photoresist is cleaned, and then the outer contour of the electrode is formed by laser cutting.

7. An easily releasable ultra-thin flexible neural electrode array prepared according to the preparation method according to any one of claims 1 to 6.

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