Direct laser writing of 3D electrodes on flexible substrates

Abstract

This report describes a 3D microelectrode array integrated on a thin-film flexible cable for neural recording in small animals. The micro electrode array fabrication process integrates traditional silicon thin-film processing techniques and direct laser writing of 3D structures at micron resolution via two-photon lithography. While direct laser writing of 3D printed electrodes has been described before, this report is the first to provide a method for high-aspect-ratio laser-written structures integrated with microfabricated electrical traces. One prototype is a 16-channel array composed of 350 micrometer long shanks spaced on a grid with 90 micrometer pitch. Other devices shown here include biomimetic mosquito-needles that penetrate through the dura of birds and porous electrodes designed to promote tissue ingrowth or enhance charge injection capacity for neural stimulation. These devices are just a few examples of a new design space that will enable high-channel-count 3D electrode arrays with features definable at single micrometer resolution. Using a custom laser writer, the 3D printing process is rapid (1 mm3/min). This high-speed printing combined with standard wafer-scale processes will enable efficient device fabrication and new studies examining the relationship between electrode geometry and electrode performance. We anticipate highest impact in small animal models, nerve interfaces, retinal implants, and other applications requiring small, high density 3D electrodes.

Direct-print three-dimensional electrodes for large-scale, high-density, and customizable neural interfaces

“…We successfully inserted these high-density microelectrodes into retinal tissue while causing minimal displacement of RGCs, resulting in high-quality recordings. The shape of the microelectrode tips could be optimized for insertion in other applications 34 . This is a direct benefit from the versatility of 2PP that is impossible to reach with conventional microfabrication processes.…”

“…This allows 3D printing with sub-micron resolution, a two-order-ofmagnitude improvement from current single-photon technologies such as stereolithographic apparatus (SLA), making it an ideal method for directly printing high-density, individually customizable structures as templates for microelectrodes. For example, Brown et al recently used 2PP to fabricate high-resolution microelectrodes onto the ends of electrical traces on flexible polymer substrates 34 . These flexible devices can be implanted to the surface of the brain, and efforts to record neural activity are currently underway, but the devices are restricted in spatial density (90-µm pitch) and channel count (16) due to the need for contacting each electrode with an electrical trace on the substrate and laser micro-machining performed on each probe to remove the passivation material.…”

Through-polymer, via technology-enabled, flexible, lightweight, and integrated devices for implantable neural probes

“…1b), with a strong emphasis on biocompatibility and mechanical flexibility. We encapsulated gold wiring in a polyimide film approximately 4 µm thick, leveraging the proven MEMS process stability and biocompatibility of polyimide 42,43 . The multistep fabrication sequence includes metal deposition, polyimide solidification, gold evaporation, and another polyimide layer, followed by reactive ion etching (RIE) device etching to expose the recording sites, bonding pads, and vias.…”

Two‐Photon Polymerization Lithography for Optics and Photonics: Fundamentals, Materials, Technologies, and Applications

“…[201][202][203][204] The generally studied silicate materials is the ORMOCER ® (Organic Modified Ceramic), which has been applied in numerous photonic applications, and also as a scaffold for cell growth and biomolecule immobilization applications. [205][206][207][208][209] Combining silicon alkoxides with monomers and other metal alkoxides makes the modification of the material properties possible for specific TPL applications, such as the silicon-zirconium hybrid SZ2080™, which is a transparent, biocompatible, and mechanically stable hybrid that can be used for complex 3D structures without shrinkage (Figure 3f). [119,[210][211][212][213][214][215][216] So far, different variants of silicon-zirconium composites have been investigated.…”