The Materials Science Foundation Supporting the Microfabrication of Reliable Polyimide–Metal Neuroelectronic Interfaces

Abstract

Thin‐film polyimide–metal neuroelectronic interfaces hold the potential to alleviate many neurological disorders. However, their long‐term reliability is challenged by an aggressive implant environment that causes delamination and degradation of critical materials, resulting in a degradation or complete loss of implant function. Herein, a rigorous and in‐depth analysis is presented on the fabrication and modification of critical materials in these thin‐film neural interfaces. Special attention is given to improving the interfacial adhesion between thin films and processing modifications to maximize device reliability. Fundamental material analyses are performed on the polyimide substrate and adhesion‐promotion candidates, including amorphous silicon carbide (a‐SiC:H), amorphous carbon, and silane coupling agents. Basic fabrication rules are identified to markedly improve polyimide self‐adhesion, including optimizing the polyimide‐cure profile and maximizing high‐energy surface activation. In general, oxide‐forming materials are identified as poor adhesive aids to polyimide without targeted modifications. Methods are identified to incorporate effective a‐SiC:H interfacial layers to improve metal adherence to polyimide, in addition to examples of alloying between adjacent material layers that can impact the trace resistivity and long‐term reliability of the thin‐film interfaces. The provided rationale and consequences of key decisions made should promote more reproducible science using robust and reliable neuroelectronic technology.

Direct laser writing of 3D electrodes on flexible substrates

“…Similarly, the current electrode uses a titanium layer above and below the platinum to bond the metal to the polymers. Delamination of this polymer/metal interface is a common failure mode for thin film electrodes, particularly at the top surface where polymer is being deposited on an oxidized layer of titanium [28]. In future iterations, this top and bottom adhesion layer could be replaced with silicon carbide to provide a superior adhesion layer between polymers and metal.…”

Microporous surface containing flower-like molybdenum disulfide submicro-spheres of sulfonated polyimide with antibacterial effect and promoting bone regeneration and osteointegration

“…6 As one of non-degradable polymers, polyimide (PI), with outstanding flexibility, mechanical strength, chemical and radiation resistance, is considered as a prospective candidate for the development of biomedical devices and implants. 7,8 PI has already been applied in biomedical fields such as neural implants for electrode arrays, electrocorticograms for large area mapping, energy harvesting devices for implanted microelectromechanical systems and dental applications. 7–9…”

“…7,8 PI has already been applied in biomedical fields such as neural implants for electrode arrays, electrocorticograms for large area mapping, energy harvesting devices for implanted microelectromechanical systems and dental applications. 7–9…”

“…6 As one of non-degradable polymers, polyimide (PI), with outstanding flexibility, mechanical strength, chemical and radiation resistance, is considered as a prospective candidate for the development of biomedical devices and implants. 7,8 PI has already been applied in biomedical fields such as neural implants for electrode arrays, electrocorticograms for large area mapping, energy harvesting devices for implanted microelectromechanical systems and dental applications. [7][8][9] As an implantable material for a bone substitute, rapid bone regeneration and osteointegration are essential prerequisites for initial as well as long-term stability, and play key roles in determination of the life of the implant.…”

Investigating the Nucleation of AlOx and HfOx ALD on Polyimide: Influence of Plasma Activation

“…This outstanding set of properties make polyimide suitable for a variety of applications ranging from electronics, medicine, membrane separation to aerospace and military industries [81,84]. Certain types of biocompatible polyimides are widely used in the packaging of implantable electronics and electrodes not only for its barrier performance [85][86][87][88][89][90][91][92][93] but also for its compatibility with microfabrication processes, being used as a structural component of devices [94][95][96][97].…”