Tunneling leakage in ultrashort-channel MOSFETs—From atomistics to continuum modeling

Abstract

The channel lengths of transistors are now nearing the nanometer, making these devices increasingly prone to direct source-to-drain tunneling (DSDT), a leakage mechanism commonly considered to set the end of Moore’s law. In MOSFETs, the probability for a charge carrier to undergo DSDT decays exponentially with channel length, source depletion length, and drain depletion length. Bound-charge engineering (BCE) is a recently introduced scheme where the depletion lengths of FETs can be controlled through effective doping by surface bound charges residing on the interface between a semiconductor and an adjacent oxide. In this letter, BCE is applied to reduce DSDT leakage current down to acceptable levels in MOSFETs with channels as short as 2.3nm; the higher the oxide permittivity, the lower the DSDT leakage. This idea is tested on ultrascaled Si nanowire MOSFETs via atomistic quantum transport simulations based on the nonequilibrium Green’s function (NEGF) formalism and the tight-binding model, as well as on physically larger Si nanosheet MOSFETs via continuum NEGF–k·p simulations based on the finite-element method.