DGSOI versus Bulk: A Quantum-Ballistic Study of 25 nm nMOSFETs

In this paper we study the performance of bulk and DGSOI nMOSFETs with 25 nm gate length in the quantum-coherent limit. The self-consistent wave functions are computed using a multi-sub-band scattering matrix formalism which allows to retain their full dimensionality and therefore eliminates the need for the adiabatic decomposition of the Schrödinger equation. We find that source-drain tunneling is negligibly small in both devices. Since the current is almost exclusively thermionic, the observed increase of the off-current with increasing drain bias can be attributed to drain-induced barrier lowering. The quantum-ballistic currents are by a factor of 2-3 larger than the quantum-drift-diffusion currents. The quantum-ballistic sub-threshold slope is almost the same for bulk and DGSOI MOSFET.