MEMS in the Nervous System 71
cords, peripheral nerves, invertebrate ganglia and other electrically active tissues.
Microwire arrays and glass pipette electrodes are still widely used for electrophys-
iological recording and stimulation. Groups have performed long term studies
in monkeys using microwire arrays, and they perform well several months after
implantation.
25
With the refinement of CMOS and MEMs processes and the development of
new techniques and equipment, silicon electrodes have become less expensive to
manufacture and more popular than before; while many groups do create their
own custom electrodes for stimulation and recording, the best known silicon
devices used in mammalian brains are the Utah Array and the Michigan Probe
electrodes.
4.2.1 The Utah Electrode Array
The original Utah array is composed of 100 pillars arranged in a 1 × 1mmsquare
base (see Fig. 4.3). It was first fabricated in the lab of Richard Normann at the
University of Utah in the late 1970s. The electrodes are electrically isolated from
one another, and signals can be individually measured from each one. Electrodes
are approximately 90 micrometers wide and 1000 to 1500 micrometers long.
26,27
These arrays have been used in primate studies and have been implanted into
humans.
28
Arrays with differing numbers of pillars can also be created; for a study
of the cat sciatic nerve, a Utah array of 25 electrodes (5 by 5 configuration) was
manufactured instead of the typical 100.
29
This particular procedure is described in Campbell et al.,
27
though alternative
methods have been explored since. The device is fabricated from a 1.7 mm thick n-
type <100> silicon wafer. Aluminum is evaporated onto the surface and patterned
into a 10 by 10 grid of 325 μm by 325 μm squares. The wafer is then heated on
Figure 4.3. The Utah Electrode Array.
26
Reprinted from Journal of Neuroscience Methods,
Rousche and Normann, 1998, Vol 82, Issue 1, pp 1–15, Copyright 1998, with permission
from Elsevier.
SO13997_text.indd 79SO13997_text.indd 79 26/01/2011 3:50 PM26/01/2011 3:50 PM

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