Statistical Analysis of Subthreshold Swing in Fully Depleted Silicon-on-Thin-Buried-Oxide and Bulk Metal–Oxide–Semiconductor Field Effect Transistors

Abstract

The variability of subthreshold swing (SS) in fully depleted (FD) silicon-on-thin-buried-oxide (SOTB) MOSFETs is statistically analyzed and compared with that of conventional bulk MOSFETs. It is newly found that SS variability is small enough in deep subthreshold region (small drain current Ids) while it increases as increasing Ids. The mechanisms of this behavior is intensively investigated and it is found that the increase in SS variability is caused by current-onset voltage (COV) variability that is due to random dopant fluctuation (RDF). Since SOTB FETs have small COV variability thanks to an intrinsic channel, SS variability is much smaller than bulk FETs, which is a great advantage of FD SOTB in terms of Ion/Ioff ratio.