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CN-122004878-A - Flexible brain-computer interface with high mechanical stability and preparation method

CN122004878ACN 122004878 ACN122004878 ACN 122004878ACN-122004878-A

Abstract

The invention relates to a flexible brain-computer interface with high mechanical stability and a preparation method thereof, belonging to the field of bioelectronics, wherein the interface comprises a flexible polyimide substrate, a composite metal microelectrode layer which is formed on the flexible polyimide substrate through a vacuum evaporation process, the composite metal microelectrode layer comprises a chromium layer which is used as a transitional bonding layer and a gold layer which is used as a conductive functional layer, the chromium layer is directly contacted with the flexible polyimide substrate to enhance the interface bonding strength, the gold layer covers the chromium layer, a photosensitive polyimide packaging layer which is formed by patterning through a photoetching process and covers the composite metal microelectrode layer and part of the flexible polyimide substrate, and the photosensitive polyimide packaging layer is provided with a window which exposes part of the gold layer of the composite metal microelectrode layer to be used as an electrode contact site and an electrode pad. The invention solves the core problems that the interface bonding force between the traditional titanium-based metal microelectrode and the flexible substrate is weak, and the mechanical-electrical stability is difficult to cooperate under long-term implantation.

Inventors

  • LIU XIANGYE
  • GAO XINBO
  • GAO JIE
  • ZHOU SUFENG
  • LI HAORUI

Assignees

  • 北京松果脑机技术有限公司

Dates

Publication Date
20260512
Application Date
20260108

Claims (10)

  1. 1. A high mechanical stability flexible brain-computer interface comprising: a flexible polyimide substrate; The composite metal microelectrode layer is formed on the flexible polyimide substrate through a vacuum evaporation process and comprises a chromium layer serving as a transitional bonding layer and a gold layer serving as a conductive functional layer, wherein the chromium layer is directly contacted with the flexible polyimide substrate so as to enhance interface bonding strength, and the gold layer is covered on the chromium layer; The photosensitive polyimide packaging layer is formed by patterning through a photoetching process and covers the composite metal microelectrode layer and a part of the flexible polyimide substrate, and the photosensitive polyimide packaging layer is provided with a window exposing a part of the gold layer in the composite metal microelectrode layer to serve as an electrode contact site and an electrode bonding pad.
  2. 2. The flexible brain-computer interface with high mechanical stability according to claim 1, wherein the thickness of the photosensitive polyimide packaging layer is 1-2 μm, and the photosensitive polyimide packaging layer completely covers all parts except the electrode contact sites and the electrode pads in the composite metal microelectrode layer to form a compact biological isolation barrier.
  3. 3. The flexible brain-computer interface of claim 1 wherein said chromium layer has a thickness of 15nm and said gold layer has a thickness of 130nm.
  4. 4. A method of preparing a flexible brain-computer interface of high mechanical stability according to any one of claims 1-3, comprising the steps of: step 1, preparing a flexible polyimide substrate on a rigid bearing substrate; Step 2, coating photoresist on the flexible polyimide substrate, and performing patterning photoetching to form an electrode pattern window; Step 3, sequentially depositing a chromium layer and a gold layer on the sample with the electrode pattern window through a vacuum evaporation process to form a composite metal layer; step 4, stripping process is carried out to remove photoresist and redundant metal above the photoresist, and a patterned composite metal microelectrode layer is obtained; Step 5, coating photosensitive polyimide on the patterned composite metal microelectrode layer to form a packaging layer film; and 6, carrying out patterning photoetching and curing on the packaging layer film to form a photosensitive polyimide packaging layer provided with a window for exposing the electrode contact site and the electrode pad.
  5. 5. The method of claim 4, wherein in step 1, the flexible polyimide substrate is prepared by spin-coating a polyimide precursor solution onto the rigid carrier substrate and performing a three-stage step heating process including low-temperature pre-bake, medium-temperature imidization curing and high-temperature post-bake to complete the curing.
  6. 6. The method of claim 5, wherein the three-stage step heating process is performed at 80-120 ℃ for 10-30 minutes, 200-250 ℃ for 30-60 minutes, and 300-350 ℃ for 1-2 hours.
  7. 7. The method of claim 4, wherein in step 2, a bilayer photoresist process is used, a layer of negative lift-off photoresist is spin-coated on the flexible polyimide substrate, and a layer of positive photoresist is spin-coated, and the exposure time is 6-10 seconds and the development time is 40-60 seconds during patterning lithography.
  8. 8. The method of claim 4, wherein in step 3, the vacuum deposition process is electron beam deposition, the vacuum degree during the deposition is not higher than 8×10 -4 Pa, the electron beam current during the deposition of the chromium layer is 0.6-0.8A, and the electron beam current during the deposition of the gold layer is 7.0-9.0A.
  9. 9. The method of claim 4, wherein in step 4, the stripping process is performed by immersing the sample in an N-methylpyrrolidone solution and performing ultrasonic treatment with a power of 50 to 100W for 5 to 10 minutes.
  10. 10. The method of claim 4, wherein in step 6, the patterning lithography is performed on the encapsulation layer film, the maskless lithography machine is used for exposure, the exposure dose is 400-600 mJ/cm2, and the encapsulation is completed after the exposure and curing at 180 ℃ for 1 hour.

Description

Flexible brain-computer interface with high mechanical stability and preparation method Technical Field The invention belongs to the field of bioelectronics, and particularly relates to a flexible brain-computer interface with high mechanical stability and a preparation method thereof. Background The brain-computer interface technology has revolutionary potential in nerve function repair, disease diagnosis and treatment and brain science research by establishing a direct communication path between the brain and external equipment. The flexible brain-computer interface is a key for realizing long-term, stable and high-precision nerve signal recording and regulation due to excellent biocompatibility and tissue compliance. The method has the core advantages of high-sensitivity signal capture, minimally invasive/noninvasive implantation adaptation and excellent biocompatibility, and shows irreplaceable application value and broad prospect in the fields of biological nerve signal accurate monitoring, human health management, clinical medical treatment and the like. The core of realizing the high-performance flexible brain-computer interface is a sensing unit-microelectrode. Microelectrodes are required to meet multiple stringent requirements of excellent electrical properties (low impedance, high signal to noise ratio), excellent mechanical stability (resistance to brain tissue micro-motion and bending and friction due to implantation operations), and long-term biostability (resistance to body fluid corrosion, inhibition of inflammatory reactions) when implanted in complex, dynamic physiological environments for long periods of time. However, prior art routes have commonly had contradictory and inherent drawbacks that are difficult to reconcile when addressing these synergistic demands. Currently, the technical development of flexible brain-computer interface electrodes mainly evolves along the following directions, but all fail to fundamentally solve the problem of long-term implantation stability: 1. in order to improve the tissue fitting degree and the comfort, the prior art designs a bionic structure such as a snake-shaped grid, fiber winding and the like or adopts a super-compliant substrate such as hydrogel, bacterial cellulose and the like. These approaches significantly improve the macroscopic flexibility and short-term biocompatibility of the device. However, the concern is often a mechanical match of the device as a whole to the tissue, and the fundamental problem of long-term firm bonding of the microscopic interface between the metallic conductive layer and the flexible polymer substrate is ignored. In a long-term dynamic physiological environment, the weak bonding interface between the metal layer and the substrate is easy to peel off due to micro motion and liquid penetration, so that the electrode is invalid. 2. Electrodes based on high performance metallic materials, noble metals (e.g., gold, platinum) are often chosen for their conductivity and chemical inertness. To enhance the bonding of metal layers to polymeric substrates, the introduction of transition layers (e.g., titanium, chromium) is a common practice in the microelectronics arts. However, in this particular application of brain-computer interfaces, simple material stacking presents a significant challenge. For example, conventional titanium (Ti) transition layers have limited bonding forces with common flexible substrates such as Polyimide (PI) and are prone to interfacial delamination (e.g., the titanium-based electrode peel failure mentioned in the background) under long-term bending and body fluid immersion. More critical is the biocompatibility of the transition layer metal (e.g., chromium) and the risk of ion exudation that may occur during long-term implantation, which are critical bottlenecks limiting its clinical transformation. The prior art lacks a design scheme of a metal layer system capable of synchronously guaranteeing high-strength interface combination and long-term biosafety. 3. Stability based on packaging technology is improved, and packaging is a necessary means for isolating physiological environment and protecting circuits. However, the traditional packaging materials and processes have poor processing compatibility with high-precision microelectrode arrays, and are easy to introduce stress, so that a packaging layer is cracked or separated from an electrode interface. More importantly, the encapsulation technology cannot be co-designed with the interface characteristics of the underlying electrode, so that it is difficult to fundamentally prevent diffusion and erosion of the corrosive medium at the interface. Partial packaging schemes may even exacerbate interfacial stress due to material modulus mismatch or improper curing process, accelerating electrode failure. In summary, the prior art presents a "split" state in which the design of the super-compliant structure is pursued to sacrifice the interface firmness