A novel compact model of quantum effects in scaled SOI and double-gate MOSFETs

Quantum-mechanical (QM) confinement of inversion-layer carriers significantly affects the threshold voltage and gate capacitance of highly scaled MOSFETs. In bulk-Si and partially depleted (PD) SOI (n)MOSFETs, the confinement is in the potential well defined by the gate-oxide barrier (which is virtually infinite) and the silicon conduction (or valence) band (the steep gradient of which defines the high transverse electric field, which controls the effect) (Stern, 1972). In ultra-thin-film fully depleted (FD) SOI and double-gate (DG) MOSFETs, the well is defined by the front- and back-gate oxide barriers, but the quantum effect can be significantly influenced by the electric field in the Si film (Majkusiak et al, 1998). Furthermore, as the film thickness (t/sub Si/) is increased, this influence becomes predominant as in the bulk-Si and PD/SOI devices. In this paper, we present a comprehensive compact model for the quantum-confinement effects for arbitrary t/sub Si/. The model, verified by numerical simulation results obtained with a self-consistent Schrodinger-Poisson solver (SCHRED; Vasileska et al, 2000), leads to characterizations of the threshold-voltage increase due to the carrier-energy quantization and the gate-capacitance reduction due to the perturbed carrier distribution.