Biomedical Engineering Reference
In-Depth Information
SCIENCE AND
TECHNOLOGY
COMMUNITIES
ACQUISITION
COMMUNITY
UNIFORMED
OPERATORS
INDUSTRY
FIGURE 4-1 Communities needed for the production, maintenance, and use of military
hardware.
(thin-film deposition and growth) and subtractive (etch) processes. This has
evolved into an enormously sophisticated enterprise, which is proven for the low-
cost, high-yield manufacture of extremely complex (~100 million transistors) and
reliable circuits. However, limitations are on the horizon. One is the difficulty of
extending today's optically based lithographic techniques to the nanoscale, which
is much smaller than ultraviolet optical wavelengths. Another is the limited num-
ber of materials used in ICs. The nanotechnology community is investigating
many disparate technologies based on many different materials, but it is far from
evident that the different processing requirements of these technologies can be
reconciled.
Self-assembly is a radically different approach to fabrication at the nanoscale.
It takes advantage of molecular and intermolecular forces to define atomic,
nanoscale, and macroscale structures. Self-assembly depends on appropriate di-
rection and control being exerted at all stages of the process by preprogramming
of the subunits or building blocks such that the required recognition elements for
self-assembly are contained in the subunits. Crystal growth is an example of self-
assembly with exquisite long-range order. Living species are proof that complex
three-dimensional structures with interacting functionality are possible. Integra-
tion of the top-down (lithography and pattern transfer) and the bottom-up (self-
assembly) approaches offers an attractive approach to bridging the current gaps
between these paradigms.
The incompatible materials issue may be addressed by individualized opti-
mization of different devices and subsystems, followed by an assembly process
akin to the automotive assembly line but at a vastly smaller scale. Here again,
top-down (pick-and-place) and bottom-up, self-assembly inspired (DNA-assisted)
approaches are among the many being investigated.
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