Fabrication and modeling of recessed traces for silicon-based neural microelectrodes

Abstract

Objective. Chronically-implanted neural microelectrodes are powerful tools for neuroscience research and emerging clinical applications, but their usefulness is limited by their tendency to fail after months in vivo. One failure mode is the degradation of insulation materials that protect the conductive traces from the saline environment. Approach. Studies have shown that material degradation is accelerated by mechanical stresses, which tend to concentrate on raised topographies such as conducting traces. Therefore, to avoid raised topographies, we developed a fabrication technique that recesses (buries) the traces in dry-etched, self-aligned trenches. Main results. The fabrication technique produced flatness within approximately 15 nm. Finite element modeling showed that the recessed geometry would be expected to reduce intrinsic stress concentrations in the insulation layers. Finally, in vitro electrochemical tests confirmed that recessed traces had robust recording and stimulation capabilities that were comparable to an established non-recessed device design. Significance. Our recessed trace fabrication technique requires no extra masks, is easy to integrate with existing processes, and is likely to improve the long-term performance of implantable neural devices.

Unprotected sidewalls of implantable silicon-based neural probes and conformal coating as a solution

“…Future work will compare these results with standard accelerating aging tests results and validate the ALD protection technique in a long-term in vivo functional study. Figure 5 shows an overview of the microfabrication process which was part of a previously in vivo-validated device technology 12,13,[44][45][46][47][48] . Four groups of devices were fabricated in this study: control (no protection), ALD-SiO 2 , ICPCVD-SiO 2 , and both ALD-and ICPCVD-SiO 2 .…”

A portable neurostimulator circuit with anodic bias enhances stimulation injection capacity

“…In the initial electrical tests, 10 kΩ, 20 kΩ, and 30 kΩ resistors were connected to stimulation channels as a working electrode output to ascertain the current conversion from biphasic voltage transient waveforms. The working electrode was a custom-designed activated IrO x microelectrode probe with 2000 μ m 2 GSA [ 27 ].…”

“…In this work, we present an upgraded and fully-portable embedded neurostimulation system that wirelessly delivers constant current stimulation signals with or without anodic bias to 16 channels and records voltage transients to monitor electrochemical safety. Validation of the system was accomplished with a custom-designed IrO x microelectrode probe [ 27 ] through extensive in vitro experiments in which anodic bias was shown to significantly enhance charge injection capacity ( Q inj ).…”