Flexible Neural Probe Fabrication Enhanced with a Low-Temperature Cured Polyimide and Platinum Electrodeposition

Abstract

Polyimide is an emerging and very interesting material for substrate and passivation of neural probes. However, the standard curing temperature of polyimide (350 °C) is critical for the microelectrodes and contact pads of the neural probe, due to the thermal oxidation of the metals during the passivation process of the neural probe. Here, the fabrication process of a flexible neural probe, enhanced with a photosensitive and low-temperature cured polyimide, is presented. Annealing tests were performed with metallic films deposited on polyimide, which led to the reduction of the curing temperature to 250 °C, with no significant irregularities in the metallic sample annealed at that temperature and an effective polyimide curing. The use of a lower curing temperature reduces the thermal oxidation of the metals during the polyimide curing process to passivate the neural probe. Additionally, in this fabrication process, the microelectrodes of the neural probe were coated with electrodeposited platinum (Pt), only after the passivation process, and its electrochemical performance was accessed. At 1 kHz, the impedance of the microelectrodes before Pt electrodeposition was approximately 1.2 MΩ, and after Pt electrodeposition, it was approximately 350 kΩ. Pt electrodeposition changed the equivalent circuit of the microelectrodes and reduced their impedance, which will be crucial for future in‑vivo tests to acquire the electrical activity of the neurons with the fabricated neural probe.

Advanced Flexible Neural Probe Design Using One-Step Chemical Vapor Deposition of Iridium Dioxide Nanoparticles for Neural System Stimulation

“…However, this reaction requires a high temperature of over 350 °C, which may change the properties of the polymer substrate when oxygen atoms are introduced. Therefore, to preserve the flexibility of the neural probes, this reaction must be modified such that it can occur at temperatures below 250 °C . Therefore, we used a unique CVD method, which was modified from ALD, introducing ozone at a low temperature.…”

“…Therefore, to preserve the flexibility of the neural probes, this reaction must be modified such that it can occur at temperatures below 250 °C. 21 Therefore, we used a unique CVD method, which was modified from ALD, introducing ozone at a low temperature.…”

High‐Resolution Recording of Neural Activity in Epilepsy Using Flexible Neural Probes

“…[ 33–35 ] The advantages of flexible probes make them attractive and promising for clinical applications as well as investigating various other neurological conditions. [ 36–38 ] However, the utility of high‐density flexible probes specifically for epilepsy monitoring remains largely unexplored. [ 39 ]…”

“…[33][34][35] The advantages of flexible probes make them attractive and promising for clinical applications as well as investigating various other neurological conditions. [36][37][38] However, the utility of high-density flexible probes specifically for epilepsy monitoring remains largely unexplored. [39] In this work, we developed and applied the advanced ultraflexible neural probes in the study of epilepsy based on mouse model.…”