Biomedical Engineering Reference
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a
10 µm
Pt electrode
Pt electrode
SiO
2
/Si
Release region
Release region
Pt electrode
Pt electrode
b
Pt wire
reservoir
plexiglas
Fig. 4.16
Top vi ew (
a
) and side view (
b
) of the neurotransmitter chip
The MEMS technology was applied to neural probes, which can be fabricated
on flexible substrates (Hollenberg et al. 2006). The array of flexible electrodes is
fabricated on a Kapton substrate, which was engineered to reduce trauma when
inserted in the region between the dura and the skull to get surface EEG recordings.
This array has 64 gold electrodes, which form an 8
8 grid, each electrode having a
diameter of 150m. This array was used to create maps of the cortical surface field
potentials lasting more than 8 h with the aim of understanding the cortical activity.
Microfabrication techniques are involved also in the development of very com-
plex arrays such as BioMEA
TM
(
Charvet et al. 2010
), which is a three-dimensional
microelectrode array having several hundreds of microelectrodes, more precisely,
256 electrodes. The electrodes were fabricated by deep reactive ion etching (DRIE)
and a combination of isotropic and anisotropic etching of Si on a glass substrate
(see Fig.
4.18
), allowing high aspect ratio of the electrodes and various shapes.
The probe contains also an analog 64-channel application-specific integrated circuit
(ASIC), which contains an amplifier and a current generator per channel. The
microelectrode arrays can be connected in various geometries (64, 128, and 256
electrodes) to various numbers of ASICs for instantaneous stimulations or recording
on all channels. This system was tested in vivo on mice.
Up to now, we have presented drug delivery chips in which the drug reservoirs
were micromachined using MEMS technology and which were interfaced with
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