On the threshold voltage of nanoscale bulk nMOSFETs with [110]/(001) uniaxial stress and quantum effects

Due to the large electron mobility gain cased by uniaxial stress along the [110] directions on (001) silicon substrate, in this paper, the impact of [110]/(001) uniaxial strain and quantum mechanical effects (QMEs) on the threshold voltage of strained-Silicon nMOSFETs is studied by developing a physically-based model. The impact of [110]/(001) stress on the band structure parameters such as density-of-state (DOS) in the conduction and valance band, band-gap and intrinsic carrier concentration is quantized first. Based on a modified threshold surface potential, the threshold voltage model is then proposed by solving the 2-D Poisson's equation and also by taking short channel effects, quantum effects and other secondary effects into consideration. Our analytical results agree with both TCAD and experimental data. The threshold voltage with the stress along arbitrary orientation can be analyzed analogously. This model can also be used for the design of nanoscale strained-Si nMOSFETs.