The challenge is that conventional transistors need V to be much higher than kT/e, where e is the electron charge, because the V is forming an electrostatic barrier that is supposed to block electrons, even when those electrons might be randomly thermally excited sometimes. The relevant technical term here is “subthreshold swing”. There is a natural (temperature-dependent) limit to subthreshold swing in normal transistors, based on thermal excitation over the barrier—the “thermionic limit” of 60mV/decade at room temperature.
The thermionic voltage of ~20mV is just another manifestation of the landauer/boltzmann noise scale. Single/few electron devices need to use large multiples of this voltage for high reliability, many electron devices can use smaller multiples. I use this in the synapse section “minimal useful Landauer Limit voltage of ~70mV” and had guessed out the concept before being aware of the existing term “thermionic limit”.
The thermionic voltage of ~20mV is just another manifestation of the landauer/boltzmann noise scale. Single/few electron devices need to use large multiples of this voltage for high reliability, many electron devices can use smaller multiples. I use this in the synapse section “minimal useful Landauer Limit voltage of ~70mV” and had guessed out the concept before being aware of the existing term “thermionic limit”.