Biomedical Engineering Reference
In-Depth Information
Gold recording site
Output leads
a
Silicon dioxide
b
c
Silicon nitride
Silicon dioxide
Interconnect
Silicon dioxide
Substrate
Silicon nitride
Silicon P+++
Silicon dioxide
Signal processing
circuit
Interconnecting
leads
Supporting
substrate
Exposed recording sites
8 µm
d
Isopotential contours
e
f
25 µV/div
4A
4C
4A
4C
4B
Axon
+.05
4
4
4
+.01
+.1
+.03
3A
3B
3A
3C
+.2
+.3
3
-.05
-.1
3
3
2A
2A
Y
2D
2A
2B
0
2
2C
2
1
-.4
2
X
Z
-.3
-.3
1
-.2
-.2
Soma
1A
-.1
1
Y
-.1
-.05
X
Z
Time T
1
Time T
2
> T
1
1 msec/div
-.05
FIGURE 8.2
Micromachined.electrodes.for.intracortical.recordings..(a-c:.from.S..L..Bement,.K. D..
Wise,.D..J..Anderson,.K..Najai,.and.K..L..Drake,.“Solid-state.electrodes.for.multichannel.multi-
plexed.intracortical.neuronal.recording”.
IEEE Trans. Biomed. Eng.
,.33,.230,.1986.).(d-f:.from.K..L..
Drake,.K..D..Wise,.J..Farraye,.D..J..Anderson,.and.S..L..Bement,.“Performance.of.planar.multisite.
microprobes.in.recording.extracellular.single-unit.intracortical.activity,”.
IEEE Trans. Biomed. Eng.
,.
35,.719,.1988..Figure.contributed.by.Khalil.Najai.and.Kensall.Wise.)
in the United States, one at the University of Michigan (Ann Arbor campus, led by Kensall Wise and
Khalil Najai) and one at the University of Utah (led by Richard Normann, who in 1995 founded
the Center for Neural Interfaces). he research that came about from these biomedical challenges
resulted in the development of the “Michigan probes” at the University of Michigan (
Figure 8.2
) and
the
“Utah electrode array” (UEA)
at the University of Utah (see the following sections). he exact
microfabrication details can be found in the literature references provided in this chapter and, in any
case, are only interesting from a historical perspective; they are conceptually similar to the methods
described in the microfabrication of cantilevers in Section 1.4.2 (
Figure 1.11
).
8.2.1 The Michigan Probes
he so-called
Michigan probes
were developed in the 1980s by a team led by Kensall Wise and
Khalil Najai and consisted of metal microelectrodes, half-exposed by insulator layers (
Figure
8.2a
) and patterned on silicon shanks (
Figure 8.2b
), which were etched by micromachining
techniques and mounted on glass pipettes before operation (
Figure 8.2c
). Some of the probes
contained active signal-processing circuits such as ampliiers. hese irst multisite simultaneous
recordings showed that activity between adjacent sites can be correlated by comparing tempo-
ral coherence (
Figure 8.2d
). Using biophysical models, the measured signals were described in
terms of axon potential propagation and soma depolarization (
Figure 8.2e
and
f
).
he materials science, electrical engineering, and biomaterials challenges associated with the
Michigan probes as outlined earlier have largely been resolved, at least for short-term small ani-
mal studies, and are now routinely fabricated in various multishank, multielectrode-per-shank
