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Current Methods of
Fabrication and Design |
| This section
outlines many forms of current technology. They are
not all considered to be forms of nanotechnology, but are provided in order to give the
reader an understanding of current developments and where nanotechnology
will fit in. |
Lithography
Current
technology using top-down
fabrication techniques has many
steps, but the most precise step involves a stream of particles or energy
which is used to etch the surface of a device into a certain pattern.
This smallest step which determines the smallest component of a design is
referred to as the "critical dimension." Currently
Optical Lithography is still the leading operation used, and involves a
focused beam of light produced by Krypton-Fluoride (KrF). It has
been found that the size of the features that can be etched into the
surface of the device is limited most significantly by the wavelength of
the light being used. KrF has a wavelength of 248 nanometers and can
produce a smallest dimension of around 250 nm, basically the same size as
the wavelength. Other possible light emission sources would be Argon
Fluoride (ArF) with a wavelength of 193nm, Fluoride Gas (F2)
with a wavelength of 157nm, and Argon Gas(Ar2) with a
wavelength of 126 nm.
It was expected long ago that optical lithography would hit some physical
boundary and that it would no longer be developed for smaller and even
smaller applications. For this reason several alternate
possibilities have been researched, but none of them are being used for
mainstream manufacturing until optical lithography hits that wall.
It will always be easier for companies to improve and modify their current
machinery rather than investing in a whole new technology. These new
technologies are E-beam lithography (which utilizes a beam of
electrons), X-ray lithography (using x-rays), Extreme Ultraviolet
Lithography (similar to x-ray but renamed), and Ion Beam Lithography.
**
All information in this box was gathered from a slide presentation by Dr.
R. J. Trew of Virginia Tech's ECE department as part of the 2001 MicrOn
lecture series. ** |
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Molecular Design and Advancements
In order to approach nanoproduction from a bottom-up approach,
there are several developmental goals which must be accomplished.
First, we must be able to pick up and place individual atoms in a
pattern. This was done first
in the IBM labs in 1989 and was quickly followed by other scientists
around the world. However,
these first atoms were noble-gases, the group of atoms that are
non-reactive and are not be attracted to each other. Real devices would be
made of atoms that would be attracted
and would bond together.
I am not sure how far they have gotten in actually constructing molecules
but I'm sure advancements are still being made in this direction.
The other task being accomplished is the design of what molecules and
structures would be useful tools. With the increasingly capable
computers that are available, a very complex model such as the interaction
of molecules can modeled and predicted. The decades of hard work by
physicists is paying off in that respect because we have numerical models
for basically every way that atoms interact, both classically and in the
quantum mechanics model.
Many websites on the Links page showcase these designs, but the
producer and forerunner in this area is the Institute
for Molecular Manufacturing (IMM).
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Self Assembly
The use of self-assembly methods is another way of producing nano-thickness
devices, utilizing the structure and properties of nature. This is a
hopeful area in further development because it does not require any
multi-million dollar equipment. In the particular method I learned
in lab this semester, called Ionically Self-Assembled Monolayers (ISAM),
certain polymer solutions are produced and then glass slides are dipped
from one beaker into another and back and forth. The glass has a
negative charge to it and will therefore attract ions from the positive
ion solution. Within a period of three minutes (wow!), no more
polymers are attaching to the surface and the slide can be rinsed and
placed into the bath of negative ions. Thus a large number of layers
can be deposited onto a slide. This approach has already been used
to create flexible diodes and even solar cells, although about a magnitude
of efficiency behind the current silicon technology.
Other techniques
involve the creation of nanotubes, or elongated Bucky Balls, and then
place additional conductive ions within them. This method is
currently being developed to create nano-transistors, |
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