Superior Work Function Variability Performance of Horizontally Stacked Nanosheet FETs for Sub-7-nm Technology and Beyond

In this paper, work function variability (WFV) of stacked nanosheet FET (NSHFET) has been numerically investigated using 3-D quantum corrected Drift-Diffusion simulation framework for sub-7nm high performance logic applications. The WFV induced NSHFET performance is investigated using RGG (ratio of average grain size to gate area) plot for fair comparison against nanowire FET (NWFET) as the effective grain size (Gsize.eff) is smaller than actual grain size (Gsize). From RGG plot analyis, it is found that NSHFET shows better immunity towards WFV induced VT variation by 15% compared to NWFET. The VT variation due to WFV is decreased by 40.47% and 29.16% for 3-stacked NSHFET and NWFET respectively compared to single stack devices. NSHFET exhibits lesser WFV induced OFF-current (IOFF) variation by 57.46% compared to NWFET. NSHFET shows better WFV induced threshold voltage mismatch index (AVT=0.7mV.μ m) compared to NWFET (AVT=1.2mV.μ m)