Physics of carrier-transport mechanisms and ultra-small scale phenomena for theoretical modelling of nanometer MOS transistors from diffusive to ballistic regimes of operation

The continuous downsizing of MOSFET geometries is motivated by the need for higher packing density and device speed together with low supply voltage operation for low-power, ultra-large scale integrated circuits. Full functionality in MOSFETs with decananometer (between 10 and 100 nm) metallurgical gate lengths has been achieved leading to mass production of devices, and MOSFETs below 10-nm gate lengths have been established. Because of their extremely small geometries, the design, fabrication and analysis of these MOSFETs involves the careful consideration and prediction of phenomena that require the understanding of device physics at the submicrometer and nanoscales. The charge-transport mechanisms and theoretical foundations for describing the functioning of small MOS devices from the diffusive to ballistic regimes of operation are surveyed. Various models of nanoMOSFET devices incorporating quantum-mechanical phenomena and velocity overshoot effect, based on the drift-diffusion, hydrodynamical and scattering approaches are discussed. The overview of nanoMOS transistors presented in this paper will serve as a useful guide for experimental and theoretical studies of these devices to gain insights into device operation, for developing physics-based models and for interpreting comprehensive simulation studies, thus paving the way to novel device concepts and innovative structural designs for the nanoMOSFET age.