Biomedical Engineering Reference
In-Depth Information
Polyimide (spin coated)
a
g
Silicon wafer
b
Metallization (Ti, Pt)
Photoresist
Metallization: electrodes,
pads, tracks
c
Spin coated polyimide
2 mm
Polyimide cover layer
h
Aluminum mask
d
Opening for contacts and electrodes
Aluminum mask
e
Photoresist
Separation of components
1 mm
f
Metal electrode
FIGURE 1.13
Metal.patterns.on.a.lexible.plastic.substrate..(From.Stieglitz,.T.,.H..Beutel,.and.J.-U..
Meyer,.“A.lexible,.light-weight.multichannel.sieve.electrode.with.integrated.cables.for.interfacing.
regenerating.peripheral.nerves,”.
Sens. Actuators A: Phys.
,.60,.240,.1997..Reprinted.with.permis-
sion.from.Elsevier.)
1.4.3 Nontraditional Substrates
he MEMS community has always pushed the development of technologies for patterning
substrates other than the traditional silicon and glass wafers, which can be conveniently spin-
coated with photoresists. Rectangular glass slides can also be spin-coated, but the photoresist
does not spread well at the edges. Strategies to pattern and handle plastics in clean rooms have
attracted the most attention in BioMEMS because plastics are cheap and lexible, which makes
them ideal candidates as interfaces with delicate body parts in disposable biomedical devices as
well as parts of cell culture devices integrated in cell culture petri dishes. One polymer that has
had good acceptance in clean rooms because of its good compatibility with silicon processing
has been polyimide. It supports metallization well and can be etched with various dry etching
steps (typically, a sacriicial aluminum mask is patterned on top of the polyimide to transfer the
pattern to the polyimide layer).
Figure 1.13
shows the fabrication process of a set of electrodes
on a polyimide ribbon intended for implantation.
Methods for microstructuring other nontraditional materials that support luid low, such as
gels, paper, and fabric, will be covered in Section 3.5, under the chapter devoted to microluidics
(Chapter 3).
1.4.4 Laser Cutting
An inexpensive CO
2
laser can be used to cut through a thin plastic roll, which conveniently comes
prepackaged with a layer of solid glue (warning: the laser actually melts the plastic, which produces
toxic fumes, so the whole apparatus must be placed in a fume hood). Each cut can be thought
of as a channel when various layers of plastic are stacked together. Melting of plastic causes the
formation of a lip at the edge of the cut that ultimately limits the resolution of the technique. his
