Experimental and theoretical investigation of the ‘apparent’ mobility degradation in Bulk and UTBB-FDSOI devices: A focus on the near-spacer-region resistance

This paper investigates the mobility `apparent' channel length dependency in nanometric devices. Based on a series of current and capacitance measurements, we report clear (V_G)^-1 dependencies of the access resistance in Bulk but also in FDSOI devices. We show that the μ_eff-L_eff degradation observed at small L can be inferred from this gate-bias dependency. By means of numerical simulation, we show that in the near-spacer-region injection velocity saturation occurs and the spreading resistance exhibits a (V_G)^-1 dependency. A comparison between Bulk and FDSOI devices clearly shows that even in the absence of LDD-counter-doping (pocket), and channel doping, the near-spacer-region resistance is far to be negligible and can contribute up to ~30% of the total resistance (r_TOT =V_D/I_DS) of a ~22nm device.