Electrons can enter or exit islands only via tunnel junctions, which is why
this field is often referred to as single-electron tunneling. Charging
effects result
in time- and space-correlated transfer of electrons. New phenomena appear,
such as Coulomb blockade which is a suppression of current flow at low bias,
and Coulomb oscillations, a
time or space correlated transfer of electrons through tunnel junctions.
With these new quantum-effects, it is possible to control the movement
and position of single electrons. Besides the desired characteristics i.e.
controlled transfer of single electrons, undesirable effects arise and
reduce or even eliminate the Coulomb blockade. These
are, for instance, co-tunneling; a simultaneous tunneling of two or more
electrons in
different tunnel junctions, or the sensitivity to uncontrollable impurities
dispersed throughout the material and to trapping-detrapping events
which disturb the charge distribution.
This thesis describes how the transport of electrons through single-electron
devices and
circuits can be simulated. Two important methods, a Monte Carlo approach and
a Master
Equation approach which treat the device as a capacitive equivalent
circuit under the action of discrete tunnel events, are compared. This
very behavior of single-electron devices makes new simulation techniques
mandatory. This thesis deals with the issue of how to
simulate co-tunneling, which is a numerically challenging problem along
with other
implementation issues, for instance, how to accelerate the simulator.
Besides the fundamental theory underlying single-electron tunneling, a
detailed study about single-electron memories is presented. Simulation
results are shown,
to exemplify the inherent possibilities of single-electron technology and to
show the
capabilities of simulation. Many important questions are
raised and examined. Is room temperature operation achievable?
Are quantum fluctuations and co-tunneling suppressible? And is the
sensitivity to
random background charges controllable?
Single-electron devices show many very promising characteristics, such as ultimate low power consumption, down-scalability to atomic dimensions and high switching speed. The result could be micro-chips with ultra large scale integration in combination with dramatically reduced power consumption. These promising characteristics give single-electron devices the potential to partially replace conventional CMOS devices in the near future.