Scaling characteristics of fNQS and ft in NMOSFETs with uniform and non-uniform channel doping

Abstract

Extensive process and device simulations are performed to investigate the non-quasi-static transition frequency (fNQS ) and unity gain frequency (ft ) behaviour of the NMOSFETs at different technology nodes, varying from 0.5 µm to 90 nm. The scaled transistors are constrained to have identical leakage current (IOFF ) at scaled voltages to facilitate a fair comparison. fNQS exhibits a turn-around in the 100 nm regime irrespective of the channel engineering. We attribute this effect to the reduced gate over-drive (VGS-Vt ) and lower mobility; which inturn degrades the transconductance (gm ). ft also shows a similar trend. The turn around effect of fNQS and ft disappears, when IOFF constraint is relaxed or the gate over-drive is increased.