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Needless to say only when room temperature operation is achieved will single-electron
devices have a noticeable impact. Liquid nitrogen operation temperature is
only acceptable for certain special applications. The bottom line from
Section 2.1 is that room temperature operation is
only possible with feature sizes below 10 nm, which is today only achievable
with granular production techniques. New material systems which
have lower dielectric permittivity or exhibit a higher quantum confinement
energy due to their reduced effective mass may reduce this spatial restriction
noticeable. Unfortunately, new materials very often require new
processes which have to be developed and studied. This takes a lot of time
and research effort. Hence the economical factor limits this possibility
drastically. Another factor for the maximum
operation temperature is the affordable error rate. In single-electron logic devices
error rates strongly depend on the temperature. Is the thermal energy, *k*_{B}*T*,
larger or of equal magnitude than the Coulomb energy, no sensible
operation is usually
possible. The first effect which is becoming prominent by lowering the
temperature or, which is equivalent, by raising the Coulomb energy, are the
Coulomb oscillations. They
are clearly visible if
*E*_{C} > 2*k*_{B}*T*. Logic devices which rely on a clear
Coulomb blockade need higher Coulomb energy, to function well. How much larger the Coulomb energy compared
to the thermal energy should be, is a question of how large an
error
rate one can afford. The range in the literature ranges from
*E*_{C}>5*k*_{B}*T* to
*E*_{C}>100*k*_{B}*T*, with
as average value.
Thus, devices that are not primarily built on the Coulomb blockade, but on Coulomb oscillations, have the
highest operation temperatures. One memory cell based on
Coulomb oscillations is reviewed in Section 5.2.9.

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*Christoph Wasshuber*