5.2.1 Operation Temperature

  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_BT, 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 > 2k_BT. 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>5k_BT to E_C>100k_BT, with $E_C\approx 30 k_BT$ 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.