Narrow-channel effects and their impact on the static and floating-body characteristics of STI- and LOCOS-isolated SOI MOSFETs

Abstract

Narrow-width effects are investigated in LOCOS and STI-isolated silicon-on-insulator (SOI) MOSFETs. With width as a parameter, variations in threshold voltage, mobility, subthreshold swing and drain-induced barrier lowering are analyzed in relationship with the other transistor dimensions (i.e. channel length, and film thickness). For both isolation techniques, a strong dependence of the threshold voltage with the channel width as well as the SOI silicon film thickness are observed while narrow and short-channel effects are not found to be correlated. Following this, it is shown through saturation subthreshold swing, latch-up and breakdown voltage measurements, that the floating-body effects (FBEs) are reduced in narrow-channel devices. Specific experiments (current transients, source–body junction current…) and simulations were conducted to reveal the mechanisms responsible for the observed weakening of the FBEs. It is concluded that three main mechanisms coexist: (i) the local thinning of the film under the LOCOS isolation, (ii) a lower carrier lifetime near the channel edges and (iii) an increase of the source/body junction leakage near the edges which speeds up the removal of the carriers from the body.