Towards the nanoscale: influence of scaling on the electronic transport and small-signal behaviour of MOSFETs

In this work, the influence of downscaling bulk MOSFETs below the 100 nm range on their static and dynamic behaviour is analysed by means of a particle-based Monte Carlo simulator. Internal transport conditions are investigated throughout the extensive information provided by numerical simulations (electric fields, concentration, velocity and energy of carriers, energy bands, etc), and a physical interpretation is given to the dynamic behaviour observed. Results show that even when the most favourable downscaling conditions are considered (that is, following the constant field scaling rules), significant two-dimensional electrostatic effects, together with reduced gate control, lead to the degradation of important figures of merit such as gate-to-source capacitance, transconductance or maximum oscillation frequency. Conventional MOSFET geometries are therefore near to a limit when reaching gate lengths of 50 nm, and the use of alternative solutions is necessary in order to maintain the proper electrostatic behaviour of a 'well-tempered' transistor.