Development of an all-SiC neuronal interface device

Abstract

The intracortical neural interface (INI) is a key component of brain machine interfaces (BMI) which offer the possibility to restore functions lost by patients due to severe trauma to the central or peripheral nervous system. Unfortunately today’s neural electrodes suffer from a variety of design flaws, mainly the use of non-biocompatible materials based on Si or W with polymer coatings to mask the underlying material. Silicon carbide (SiC) is a semiconductor that has been proven to be highly biocompatible, and this chemically inert, physically robust material system may provide the longevity and reliability needed for the INI community. The design, fabrication, and preliminary testing of a prototype all-SiC planar microelectrode array based on 4H-SiC with an amorphous silicon carbide (a-SiC) insulator is described. The fabrication of the planar microelectrode was performed utilizing a series of conventional micromachining steps. Preliminary data is presented which shows a proof of concept for an all-SiC microelectrode device.

Demonstration of a Robust All-Silicon-Carbide Intracortical Neural Interface

“…Capacitance versus voltage measurements of Schottky contacts to the n + layer verified that the doping on the n + epi layer was on the order of 3.45 × 10 18 cm −3 which was consistent with our epi-doping estimates of ~3 × 10 18 cm −3 from prior growth runs using the same level of intentional nitrogen doping [ 38 ]. Typical doping of the p-type base epitaxial layer was ~1 × 10 16 cm −3 .…”

“…Five all-SiC electrodes of increasing geometrical surface area, via doubling electrode diameter from 25 to 800 µm (200 µm was left out to save real estate), were characterized electrochemically in PBS. Our previous investigation evaluated only 25 µm diameter electrodes and demonstrated capacitive interaction with little Faradaic activity [ 38 ]. That study demonstrated that 4H-SiC fits the same electrochemical model as reported for semiconductor electrodes [ 41 , 78 ].…”

“…The fabrication sequence to realize the all-SiC microelectrode devices was detailed in Bernardin et al [ 38 ]; however, it has since been refined as explained here. Figure 1 a shows the mask design used to produce the single-ended all-SiC electrodes (top) and the test structures (bottom).…”

“…Two structures were fabricated to characterize the electrical capabilities of the all-SiC devices. In Bernardin et al [ 38 ], all of the electrodes tested were of a single size with a 25 µm recording tip diameter, but varied in lead length from 4 to 10 mm. While we established that trace length did not significantly affect the overall electrical impedance, it has been shown that the geometrical surface area (GSA) of an electrode can be an important factor in overall performance [ 24 ].…”

Fabrication of a Monolithic Implantable Neural Interface from Cubic Silicon Carbide

“…Helium (He), with a flow rate of 700 sccm, was used as the carrier gas. The RF power was set to 200 W, substrate temperature to 300 °C, and pressure to 1100 mTorr [37,38]. Following photoresist patterning using AZ 15nXT-450 CPS negative photoresist (Microchemicals GmbH), a reactive ion etch (RIE; PlasmaTherm) was run for 210 s to open windows in the a -SiC film for the electrode sites.…”