Quantum-mechanical effects in nanometer scale MuGFETs

Abstract

Solving the Poisson and Schrödinger equations self-consistently in two dimensions reveals quantum-mechanical effects that influence the electron concentration, the threshold voltage and the subthreshold slope of MuGFETs. The average electron concentration needed to reach the threshold voltage depends on the gate configuration and on the device geometry. The dependence of the energy of the subbands on the different gate configurations is studied, and the relation between threshold voltage and the lowest subband energy is investigated. Due to a dynamic threshold voltage effect, the drain current is lower in the quantum-based drain current model than in classical simulations. This dynamic increase of threshold voltage is due to an increase of the subband energy with the electron concentration. This effect degrades the subthreshold slope. It is observed in non-symmetrical devices (FinFET, tri-gate), but not in symmetrical structures (GAA). This gives symmetrical devices like GAA nanowires an intrinsic advantage compared to the other types of devices.