Ballistic/quasi-ballistic transport in nanoscale transistor

The current voltage characteristics of the silicon ballistic MOSFETs are introduced and discussed. They are derived by considering the current capacity through the bottleneck point in the channel, and they provide a simple measure of the performance limit. The performance of experimental nanoscale bulk MOSFETs are compared with the ideal ballistic limit. It was shown that the performance degradation due to carrier scattering amounts to several to several tens percent in recent nanoscale MOSFETs. Quasi-ballistic transport in MOSFETs was also analyzed by a simple approach based on the transmission viewpoint. Channel-length reduction was found to yield consistent improvement of the ballisticity. Considerable performance degradation, however, was still found to persist even in 10-nm MOSFETs. The role of each carrier scattering mechanism is analyzed. It is shown that elastic scattering degrades the performance, but the inelastic energy relaxation improves the performance of the MOSFET.