Transition from high to low $1/f$ noise regimes in Field Oxide Field Effect Transistors (FOXFETs)

The excess low frequency ($1/f)$ noise of parasitic field oxide FETs from a 130 nm technology has been found to vary by more than $\sim $6 orders of magnitude with gate voltage, above the nominally measured device threshold. We find that this variation is due to a transition from noisy subthreshold conduction to full conduction in strong inversion at a point that is more than 5 V above the standard extrapolated threshold voltage. This field oxide structure has a length of $\sim $ 1 micron and a width of $\sim $ 200 micron. We attribute the conduction below to a noisy, subthreshold (perhaps even percolative) path at lower voltages, with a significant contribution from the high density of defects at the Si/SiO$_{2}$ interface in this parasitic FOXFET structure. The noise above the ?true? threshold (as determined with assistance from the noise measurements) follows a standard number fluctuation model, when the subthreshold conduction regime is separated out in the analysis. This work was supported in part by the US Navy.