Numerical Investigation of Short-ChannelEffects n Negative Capacitance MFIS and MFMIS Transistors: Subthreshold Behavior

We present a detailed TCAD analysis of the impact of length scaling and the associated short-channel effects in the subthreshold regime of the two classes of double-gate negative capacitance transistors (NCFETs): metal-ferroelectric-metal-insulator- semiconductor (MFMIS) and metal-ferroelectric-insulator- semiconductor (MFIS). Our TCAD formulation takes into account both the out-of-plane and in-plane components of ferroelectric polarization. Contrary to the conventional FETs, both the configurations of NCFETs exhibit increase in the threshold voltage (V-t), reduction in subthreshold swing (SS), and drain-induced barrier lowering with scaling due to inner and outer fringing electric field effects. The existence of the internal metal layer causes these effects to be significantly higher in the MFMIS structure than the MFIS, where the fringing field impact remains confined to the channel edges only. The above-mentioned unconventional short-channel effects increase with the inclusion of spacer regions of high permittivity in both the MFMIS and MFIS devices. We also analyze the impact of source/drain doping on fringing field coupling to the ferroelectric and find that a higher doping of these regions improves the subthreshold characteristics of NCFETs, in contrast to conventional FETs.