Mapping diverse hysteresis dynamics in scaled MoS$_2$ FETs using the universal method derived from TCAD modeling

Abstract

Field-effect transistors (FETs) based on 2D materials have already reached the stage of trial FAB integration. However, reliability limitations caused by various defects present a serious obstacle for their smooth way forward, especially when scaling the device geometries. Still the ongoing research is mostly focused on pure technology aspects, while reliability is often recalled only when showing a randomly measured gate transfer curve to manifest that the hysteresis is "negligible".In fact the hysteresis dynamics contain unique fingerprints of various mechanisms which may coexist or cancel each other, being more complex in scaled FETs, for instance because of simultaneous interaction of defects with the channel and top gate in thin insulators. To fill this gap, here by doing TCAD modeling for nanoscale MoS$_2$/HfO$_2$ FETs we introduce the universal hysteresis mapping method which can correctly capture commonly measured diverse hysteresis dynamics such as conventional clockwise (CW) and counterclockwise (CCW) hysteresis, as well as CW/CCW switching and time separation. Next we extend this method to bias-temperature instabilities (BTI) and show a clear correlation between complex hysteresis dynamics and abnormal BTI recovery. Finally, we validate our mapping method using available experimental data for MoS$_2$ FETs and demonstrate that it provides far more accurate results than a conventional constant current extraction of the hysteresis width, being also usable if a CCW hysteresis is caused by mobile ions.