Gate Fringe-Induced Barrier Lowering in Underlap FinFET Structures and Its Optimization

The difficulty to fabricate and control precisely defined doping profiles in the source/drain underlap regions of FinFETs necessitates the use of undoped gate underlap regions as the technology scales down. We present a phenomenon called the gate fringe-induced barrier lowering (GFIBL) in FinFETs with undoped underlap regions. In these FinFETs, we show that the GFIBL can be effectively used to improve I_on. We propose the use of high-kappa spacers in such FinFETs to enhance the effect of GFIBL and thereby achieve better device and circuit performance. When compared with the underlap FinFETs with Si₃N₄ spacers, with kappa=20 spacers, we show that it is possible to achieve an 80% increase in I_on at iso-I_off conditions and a 15% decrease in the inverter delay for a fan-out of four.