Observation of mobility and velocity behaviors in ultra-scaled LG=15 nm silicon nanowire field-effect transistors with different channel diameters

Abstract Experimentally, two critical device performance factors, apparent mobility (μapp) and virtual source velocity (vx0) were investigated down to effective channel length (Leff) = 15 nm silicon nanowire field-effect transistors (SNWFETs) by using virtual source (VS) model. Both μapp and vx0 decreased in n-SNWFETs but increased in p-SNWFETs as the nanowire diameter (DNW) shrank because of opposite effective mass (meff) dependency. The critical on-current booster, vx0 rather than μapp increased monotonically as Leff shrank, and it showed that vx0 boosting by Leff scaling is still valid to Leff= 15 nm in SNWFETs. Furthermore, p-SNWFETs had higher μapp and vx0 than n-SNWFETs because compressive stress from SiGe layer below source/drain improved the performance of p-SNWFETs. Interestingly, unpredicted non-linearity of Leff/μapp vs. 1/vx0 plot was observed in short channel p-SNWFETs and its origin was discussed. Finally, thermal limit velocity (vTx) and ballistic efficiency (Bsat) consisting vx0 were extracted from experimental data. The DNW dependence of vTx and Bsat was analyzed using stress effect, meff, critical length (LC), and mean free path (λ), which provides the way of vx0 boosting.