NEGF Simulation of Nanoscale MOSFETs with Anisotropic Si Permittivity

Abstract

CMOS scaling has led to several issues that are necessary to be investigated further In this thesis the transport behavior of electrons in a nanoscale double-gate (DG) MOSFET is modeled by solving Schr?dinger equation in non-equilibrium Green’s function (NEGF) formalism which is solved self-consistently with the Poisson equation to obtain the potential profile electron density transmission coefficient and thus the drain current versus gate voltage (I_DS-V_GS) curves In addition to quantum effects which have been taken into account in the transport equation the reduction of permittivity in the surface region and the anisotropic permittivity that influence the electrical properties are investigated and their influences on the electrical characteristics of MOSFETs are discussed It is shown that the reduction of permittivity in the surface region slightly improves the subthreshold swing and slightly increases the threshold voltage due to the increase of the potential barrier for electrons in the transport direction This suggests the better immunity to SCEs for materials of the channel with smaller permittivity In the case of anisotropic permittivity the subthreshold swing degrades and the off-leakage current becomes higher as the permittivity in the confinement direction becomes smaller due to the decrease of the potential barrier in the transport direction This suggests the better immunity to SCEs for materials of the channel with larger permittivity in the confinement direction For long channel devices the variation in permittivity barely changes the potential barrier in the transport direction Therefore the variation in the permittivity has neglecting effects on the (I_DS-V_GS) characteristic

Date of Award	2019
Original language	English
Supervisor	Kuo-Hsing Kao (Supervisor)