  In this chapter we intend to discuss the major trends in the evolution of
microelectronics and its eventual transition to nanoelectronics. As it is well
known, there is a continuous exponential tendency of microelectronics towards
miniaturization summarized in G. Moore's empirical law. There is consensus that
the corresponding decrease in size must end in 10 to 15 years due to physical
as well as economical limits. It is thus necessary to prepare new solutions if
one wants to pursue this trend further. One approach is to start from the
ultimate limit, i.e. the atomic level, and design new materials and components
which will replace the present day MOS (metal-oxide-semi- conductor) based
technology. This is exactly the essence of nanotechnology, i.e. the ability to
work at the molecular level, atom by atom or molecule by molecule, to create
larger structures with fundamentally new molecular orga- nization. This should
lead to novel materials with improved physical, chemi- cal and biological
properties. These properties can be exploited in new devices. Such a goal would
have been thought out of reach 15 years ago but the advent of new tools and new
fabrication methods have boosted the field. We want to give here an overview of
two different subfields of nano- electronics. The first part is centered on
inorganic materials and describes two aspects: i) the physical and economical
limits of the tendency to miniaturiza- tion; ii) some attempts which have
already been made to realize devices with nanometric size. The second part
deals with molecular electronics, where the basic quantities are now molecules,
which might offer new and quite interest- ing possibilities for the future of
nanoelectronics
