  Thermally activated sub-threshold transport has been investigated in undoped
triple gate MOSFETs. The evolution of the barrier height and of the active
cross-section area of the channel as a function of gate voltage has been
determined. The results of our experiments and of the Tight Binding simulations
we have developed are both in good agreement with previous analytical
calculations, confirming the validity of thermionic approach to investigate
transport in FETs. This method provides an important tool for the improvement
of devices characteristics.
