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Nanoelectronics
encompasses nanoscale circuits and devices including (but not limited to)
ultra-scaled FETs, spin devices, superlattice arrays, quantum coherent devices,
molecular electronic devices, and carbon nanotubes.
Over
the past four decades, electronic components have grown more powerful as the
transistor, has shrunk in dimensions by several factors. However, the laws of
quantum mechanics, and the limitations of materials and fabrication techniques
are making it very difficult for further reduction in the minimum size of
today's semiconductor transistors. Researchers have projected that as the
overall size of the bulk-effect, semiconductor transistor is aggressively
miniaturized to approximately 0.1 micron (i.e., 100 nanometers) and beyond the
devices may no longer function as well.
Thus,
in order to continue the miniaturization of integrated circuits well into the
next century, it is likely that present day, micron-scale microelectronic device
designs will be replaced with new designs for devices that take advantage of the
quantum mechanical effects that dominate on the much smaller, nanometer scale.
(Note that 1 nanometer, abbreviated nm, is one billionth of a meter or 10 atomic
diameters.)
The
nanoelectronic devices are subdivides into two broad areas, as follows:
o
Solid-state
quantum-effect nanoelectronic devices
o
Molecular
electronic devices
Solid-state
quantum-effect nanoelectronic devices are used to continually increase the density and speed of information processing. This
technology, which changes the operating principles, but not the fabrication medium for integrated circuits, might extend Moore's Law of
electronics miniaturization to produce devices down to a few tens of nanometers.
Present-day field effect transistors (FETs)
on commercial integrated circuits are approximately 1 micron or 1000 nm across,
and it is believed that bulk-effect
FETs will cease to function effectively when their gate
lengths dip below 25 nm, which corresponds to an overall device length of
approximately 100 nm.
On the other hand, quantum-effect switching devices tend to function better when they are made smaller. Solid state quantum-effect nanoelectronic devices might be made as small as approximately 12 to 25 nanometers across and still expected function effectively.
A
number of solid-state nanoelectronic switching devices have reportedly been
fabricated, and prototype solid-state nanoelectronic processors
are demonstrated. As a result of nanometric scale, significant reduction
could result in ultra-fast, low power integrated circuits with billions of
transistors on a single CPU chip, and Terabyte memories on a chip.
Such
advances would require, reliable fabrication of devices and circuits with only 5
to 10 nanometers wide. This is about 10-20 smaller than that achievable using UV
lithography.
Molecular
electronics, using individual covalently bonded molecules to act as wires and
switching devices, is expected to bring the Moore's Law down to nanometer scale. Individual
molecular switching devices could be as small as a few nanometers. This
decrease in size could result in Terabyte memories on a chip and in excess of
one trillion switching-devices on a single CPU chip. A primary advantage of
molecular electronics is that molecules are natural nanometer-scale structures
that can be made absolutely identical in vast quantities. Also, synthetic
organic chemistry offers more options for designing and fabricating these
intrinsically nanometer-scale devices than the technology presently available
for producing solid-state chips with nanometerscale features.
The subject of molecular wires is of primary significance, even in an overview of nanoelectronics switching devices. Molecular wires are used to demonstrate conductance in a single molecule.
Quantum-effect Molecular electronic devices
Using
molecular structures for quantum confinement might make it possible to
manufacture fast, quantum-effect switching devices on a large scale more
uniformly and cheaply than has thus far been feasible with solid semiconductors.
Electromechanical Molecular electronic devices
Electromechanical
molecular switching devices are not so closely analogous to microelectronic
transistors as are the molecular devices. Deforming or re-orienting molecular
structures is the underlying principle in of an Electromechanical molecular
electronic. An Electromechanical molecular switch does not use electron charges
like microelectronic switch. The input is also normally mechnical. However, just
like all those other switches, they can turn on or off a current between two
wires, which makes them interesting for nanocomputing.
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