Biomedical Engineering Reference
In-Depth Information
Appendix. Teaching Materials
A.1 Suggested Exercises for Chapter 1
Exercise A.1.1.
Briely describe the basic elements of and diferences between photolithography,
sot lithography, and micromachining.
Exercise A.1.2.
Describe how to make a trench in silicon with (a) pyramidal walls and
(b) vertical walls. (If you know more than one way, please describe them.)
Exercise A.1.3.
Describe the conceptual diferences between photolithography, micro-
stamping, and microluidic patterning, putting an emphasis on their relative advantages and
disadvantages.
Exercise A.1.4.
Describe ive important properties of PDMS in the context of sot lithog-
raphy. Briely explain whether each property is advantageous or disadvantageous for build-
ing microdevices (note that it can be both, depending on the context of its use), and why you
think so.
Exercise A.1.5.
Choose from the literature (e.g.,
Figure A.1a
) a picture of a metal pattern
on a lat surface and describe at least four processes, two photolithographic and two sot litho-
graphic, that could have been used to produce it. Is it possible to use the same technique to
produce the reverse pattern, and if so, how would it be done? Be as speciic as possible about the
chemistry employed at each step and use step-by-step cross-sectional schematics to illustrate
your explanations.
Exercise A.1.6.
Choose from the literature (e.g.,
Figure A.1b
) a picture of a structure that
has been micromachined on Si(100) and describe at least two processes, one photolithographic
and one sot lithographic, that could have been used to produce it. Be as speciic as possible
about the chemistry employed at each step and use step-by-step cross-sectional schematics to
illustrate your explanations.
Exercise A.1.7.
Imagine that you are prototyping a device and need to write the patterns
shown in
Figure A.2
in 40-μm-thick SU-8 photoresist on a silicon wafer (required exposure
energy of 160 mJ/cm
2
).
You have the following tools available:
(a) A variable aperture lash-and-repeat laser writer—this tool has a laser light source
and a rectangular aperture with dimensions (length and width) that can be varied
from 2 μm to 1.5 mm in 0.5-μm increments. he aperture can rotate and the sample
stage can translate. Each lash exposes a rectangular feature at an exposure energy of
40 mJ/cm
2
. he exposure region corresponds to the aperture size at a location that is
determined by the stage translation. he machine is capable of 3000 lashes/hour.
he stage translation time is negligible compared with the exposure time.
(b) A raster-scan laser writer. his tool has a 3-μm spot size laser light source that is
raster-scanned over the entire region of the sample to be patterned and the light is
either allowed to reach the substrate or delected for pixels that are not to be written.
he tool writes 30 mm
2
/min at a scan rate of 1×, corresponding to an exposure energy
of 40 mJ/cm
2
. Scan rates of 2× and 4× are also available.
(c) A laser-illuminated digital mirror device (DMD). he DMD has an array of 1024 ×
768 square mirrors that are 13 μm × 13 μm. he DMD is illuminated with the laser
and the light is relected through a lens with a demagniication factor of 5:1 onto the
sample surface. he optical power density that reaches the sample surface is 4 mW/
