Impact of S/D Extension Length and Sheet Stacking on Transient Behavior of Nanosheet FETs

The impact of source/drain extension length (LEXT) and vertical sheet stacking on the transient response of the inverter, made up of nanosheet FETs, has been investigated. This study mainly focuses on overshoot/undershoot in the transient behavior of the inverter in continuation with its impact on propagation delay. It has been observed that propagation delay reduces with a symmetric increment of S/D LEXT. However, 4 ~ 5 nm of LEXT would be the optimum choice for source/drain extension length considering overshoot/undershoot. Away from this range of LEXT, a continued increment in overshoot/undershoot is observed owing to the increment/decrease in gate-to-drain resistance/capacitance, respectively. Furthermore, circuit level analysis done on the desire for high-drive capability through vertical sheet stacking shows that increasing sheet stacks decreases the propagation delay, as well as it also increases the overshoot/undershoots, which may damage the in-path level sensitive devices on an increased voltage level at the output of the inverter.