Online proceedings - EDA Publishing Association

(BNCD) as the active microelectrode material, our approach is
based on a bottom-up patterning process [12], fully compatible
with standard clean room fabrication methods.
In this process, see Figure 1, the wafer (typically oxidised
silicon) undergoes at first a nano-seeding operation on its
entire surface by spreading a colloidal solution of diamond
nano-particles in suspension in ethanol (example of nanoparticle
solution: provided by SP3 SEKI Technotron). Then, a
protective sacrificial metal layer is used as hard mask to
protect the nano-particles while the unprotected regions are
etched away using an oxygen/argon plasma RIE step.
This step required technological optimization and results are
reported in figure 2. One can see that after 10 minutes of
plasma exposure, the crystal density decreases below 10 6 cm -2 ,
and after 20 minutes duration of the plasma exposure, the
changes in crystal density becomes non significant, which
corresponds to the end of this etching phase. Indeed all
diamond nano-particles originating from the nano-seeding
have been etched away and the residual density is mainly due
to surface defects, the nano-seeding density remaining above
10 10 cm -2 on non etched surfaces while reaching only 5.10 5
cm -2 on etched surfaces.
Finally, the protective metal layer is completely removed
considering that it is not affecting significantly the nanopowders
immobilized onto the substrate surface. One
difficulty here was the control of the uniformity of the nanoparticle
distribution.
The final step is the local growth of diamond on pre-defined
patterned electrodes.
11-13
May 2011, Aix-en-Provence, France
Residual density (cm -2 )
1,0E+09
1,0E+08
1,0E+07
1,0E+06
1,0E+05
1,0E+04
0 5 10 15 20 25
Plasma etching duration (min)
Figure 2. Residual nucleation density of diamond nanoparticles
versus plasma etching duration.
III.
MEA FABRICATION AND CHARACTERISATIONS
The technological fabrication route for MEAs implies a
similar process as the one described in part II. MEAs can be
done either with (i) the local growth of diamond on existing
metal electrodes (Titanium) and using Si 3 N 4 for insulation, or
(ii) with the homogeneous growth of diamond followed by the
definition of annular metallic contacts. The top side
passivation is ensured using SU8. Both solutions have been
tested, see Figure 3.
i)
ii)
Figure 3. Diamond based MEA using the process i) or ii).
Figure 1. Diamond based Microelectrode fabrication process.
Fabricated MEAs are characterised using electrochemical
measurements in ferri/ferrocyanide 1mM (cyclic voltametry
and Electrochemistry Impedance Spectrocscopy (EIS)) and
their performances are compared with that of Pt identical
devices.
In-vitro B-NCD MEAs were tested with retina of rat, i.e. (i)
cultures of ganglion cells (CGC) and spinal cords, i.e. (ii)
organotypic cultures of mouse spinal cords. The tests
demonstrated that no difference could be observed with
respect to glass control, see Figure 4. Also, no proteinic
coating was found to be necessary to ensure cell growth.
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