Development of silicon electrode enhanced by carbon nanotube and gold nanoparticle composites on silicon neural probe fabricated with complementary metal-oxide-semiconductor process

Abstract

We present the fabrication of highly P-doped single crystal silicon electrodes on a silicon probe through complementary metal-oxide-semiconductor (CMOS)-compatible processes. The electrode with diameter of 50 μm and a separation of 200 μm is designed for recording/stimulating purposes. Electrochemical impedance spectroscopy indicates that the interfacial impedance of silicon electrodes at 1 KHz is 2.5 ± 0.4 MΩ, which is equivalent to the result reported from the gold (Au) electrode. To further enhance the charge storage capacity, composites of multi-wall carbon nanotubes (MWCNTs) and Au nanoparticles are electroplated onto the highly P-doped silicon electrode after surface roughness treatments. With optimized electroplating processes, MWCNTs and Au nanoparticles are selectively coated onto the electrode site with only a minimum enlargement in physical diameter of electrode (<10%). However, the typical impedance is reduced to 21 ± 3 kΩ. Such improvement can be explained by a boost in double-layer capacitance (Cdl) and the reduction in faradic resistances. The measurement of cyclic voltammetry (CV) shows that the cathodal charge storage capacity is up to 35 mC cm−2, which proves the superior performance of composite coatings on silicon electrodes and validates the functionality of reported CMOS-compatible silicon probe.