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

Abstract

Intracortical neural interfaces (INI) have made impressive progress in recent years but still display questionable long-term reliability. Here, we report on the development and characterization of highly resilient monolithic silicon carbide (SiC) neural devices. SiC is a physically robust, biocompatible, and chemically inert semiconductor. The device support was micromachined from p-type SiC with conductors created from n-type SiC, simultaneously providing electrical isolation through the resulting p-n junction. Electrodes possessed geometric surface area (GSA) varying from 496 to 500 K μm2. Electrical characterization showed high-performance p-n diode behavior, with typical turn-on voltages of ~2.3 V and reverse bias leakage below 1 nArms. Current leakage between adjacent electrodes was ~7.5 nArms over a voltage range of −50 V to 50 V. The devices interacted electrochemically with a purely capacitive relationship at frequencies less than 10 kHz. Electrode impedance ranged from 675 ± 130 kΩ (GSA = 496 µm2) to 46.5 ± 4.80 kΩ (GSA = 500 K µm2). Since the all-SiC devices rely on the integration of only robust and highly compatible SiC material, they offer a promising solution to probe delamination and biological rejection associated with the use of multiple materials used in many current INI devices.

Fabrication of a Monolithic Implantable Neural Interface from Cubic Silicon Carbide

“…Aluminum and nitrogen were the p and n dopants, respectively, and were introduced during the epitaxial growth process [35,36]. The doping level of the top n + 3C-SiC film was measured with a LEI 2017b Mercury (Hg) Probe (Lehighton Electronics, Inc., Lehighton, PA, USA) [33].…”

“…The breakdown voltage occurs when the current rapidly increases during application of negative voltage. The root mean square (rms) of the current amplitude between breakdown and forward potentials for the diodes was defined as reverse leakage current [33]. The threshold current for defining the breakdown voltages was 10 µA.…”

“…In our previous work, we reported the fabrication and characterization of nearly monolithic MEAs made from 4H-SiC, a hexagonal polytype of crystalline SiC, with a -SiC insulation [33]. However, the manufacture of these devices, as well as their release from the bulk SiC wafer, made these devices difficult to fabricate and costly.…”

Amorphous Silicon Carbide Platform for Next Generation Penetrating Neural Interface Designs

“…Amorphous SiC was chosen because it exhibits robust chemical inertness [ 36 ], high electronic and ionic resistivity [ 37 ], biocompatibility [ 37 , 38 , 39 , 40 ], and is amenable to thin-film fabrication processes [ 35 ]. Crystalline SiC has also been used as a material in the fabrication of MEAs and, because it is a wide bandgap semiconductor that can be doped for electronic conductivity, it may be used for conductive traces or as a low-impedance electrode, as well as an insulator [ 41 , 42 , 43 , 44 , 45 ]. The 16 channel MEAs were developed with two a-SiC layers sandwiching a thin-film Au conducting trace.…”

Correction: Bernardin E.K.; et al. Demonstration of a Robust All-Silicon-Carbide Intracortical Neural Interface. Micromachines, 2018, 9, 412

“…The authors would like to indicate the following financial support they received to the Acknowledgement Section of their published paper [ 1 ]: “The Florida Education Fund’s McKnight Doctoral Fellowship Program and the Alfred P. Sloan Foundation University Center of Exemplary Mentoring (UCEM) are gratefully acknowledged for providing financial support to Evans K. Bernardin during this research.”…”