MSc subject
SiC microelectrode arrays incorporating nanowire networks for ex-vivo characterization
Thesis background:
Nervous system damage and disorders come in a variety of forms and rarely heal over time. Millions of individuals
worldwide suffer from physical disabilities that are a direct result of damage to their central nervous system (CNS);
thousands more have lost limbs due to wartime violence and have suffered damage to their peripheral nervous
system (PNS). In addition, neurodegenerative diseases and conditions, such as Alzheimer, Parkinson’s disease,
epilepsy, depression, and schizophrenia, are affecting a growing number of individuals globally. The brain machine
interface (BMI) or neurointerface technology also known as the brain-computer interface (BCI) shows great promise
to be able to provide therapeutics for these types of injuries [1].
In the field of BMI devices, researchers are not still able to produce clinically viable solutions that meet the
requirements of long-term operation due to biological, material, and mechanical issues. Most of the issues are due
to biotic and abiotic sources related to the employed materials for BMI fabrication. Biotic mechanisms of failure are
related to the brain inflammatory response to implanted system. Abiotic mechanisms correspond to the stability of
the implanted system in the brain environment.
Objective :
Hereby, we propose the use of SiC as the base and single material for the fabrication of the electrodes in BMI
systems. It is also proposed to include SiC nanowires in the electrodes probe area. Towards this purpose
microelectrode arrays (MEAs) will be fabricated for the in-vitro investigation of SiC as electrode material.
Why SiC?
Various in vitro and in vivo studies have shown that this material is suitable for use in biomedical devices [2, 3, 4].
Indeed, SiC is a semiconductor that is completely chemically inert within the physiological environment, resists
oxidative corrosion and has demonstrated no appreciable toxicity [5, 6, 7]. In addition, SiC electrode probes are
characterized by an excellent neural compatibility. Cubic silicon carbide (3C-SiC) is highly compatible with central
nervous system (CNS) tissue in a murine mouse model [8]. In a later study [9], it has been demonstrated a robust all3C-SiC intracortical neural interface (INI) for advanced bionics and brain-machine interfaces (BMI). Similar devices
based on 4H-SiC polytype exhibited better performance in terms of electrochemical response [10, 11, 12].
SiC can also address successfully abiotic issues. Silicon carbide (SiC) is extremely suitable for the fabrication of the
implantable electrode incorporating all three functions: support, conductors and insulation. Indeed, SiC current
technology maturity (many SiC devices are commercially available) offers this possibility. The support can be
micromachined using conventional methods available to the Si industry. Doping the semiconductor into the metallic
regime can create the conductors. Lastly, the insulation can be achieved by using amorphous insulating SiC. By
reducing the heterogeneity of the materials comprising microelectrode arrays, we can improve the reliability of
these devices (abiotic response).
Other semiconductors fall short in providing a platform for single material electrodes. In addition to the mechanical
limitations of Si, its low bandgap reduces the blocking voltage and limits electrical isolation [13]. Indeed, SiC-based
diodes have higher turn-off voltage (well above 1V) than Si (0.6V) warranting a small cross-talk in multi-electrode
probes. Many semiconductors are toxic (aka gallium arsenide [14]), experience anodic oxidation and corrosion
(diamond [15], gallium nitride[16])), or have extremely large bandgap and resistivity (boron nitride [17]).
In addition to the excellent bio- and hemocompatibility, SiC has a fracture toughness 4-5 times greater than Si as well
as better buckling characteristics. Thus, SiC probes can be thinner and more compliant than the current implantable
devices, which may lead to a reduced biotic response.
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Why SiC Nanowires (NWs)?
A low impedance is desired for the reduction of shunt pathways and to increase signal to noise ratio [18, 19]. Our
proposal, is to reduce impedance using the relationship between the geometric surface area and electrochemical
reaction by employing SiC NWs. This requirement is related to do specific recording (requiring a small probe area like
in the case of key CNS components) with max signal (‘ultramicroelectrodes’). Note that small probe area results in
better biotic response. Thus, our novel approach relies on using SiC NWs to increase the recording signal.
Workplan
In the frame of the present thesis, the MSc
candidate will develop the initial stages for the
development of a new implantable electrode based
on SiC material and nanowires. More precisely
planar microelectrode arrays will be fabricated and
characterized. A typical configuration for such MEA
is shown in the figure aside. The comprehensive
effort will include SiC NW formation, electrode
fabrication and electrochemistry characterization.
The work will be principally performed in the
ATLASNEuro, Louvain, Belgium in collaboration the
lab IMEP-LAHC in Grenoble, France and MRGFORTH in Heraklion, Greece.
Fig. Schematic of the MEA. The diameter of the active site will be
between 20 and 80μm
The main steps of the workplan are:
 Detailed bibliography.
 Design of the MEA and the corresponding process steps
 Design of the photolithography mask set
 Optimization of technology steps (plasma etching, ohmic contacts)
 Fabrication of the MEA without nanowire network
 Electrochemical evaluation of the MEA without nanowire network.
 Fabrication of the MEA with nanowire network
 Electrochemical evaluation of the MEA without nanowire network.
Contact:
For further information contact:
Dr. Arno Aarts
aarts@atlasneuro.com
Dr. Konstantinos Zekentes
zekentesk@iesl.forth.gr
References :
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