F. Crupi et al., ON THE PROPERTIES OF THE GATE AND SUBSTRATE CURRENT AFTER SOFT BREAKDOWN IN ULTRATHIN OXIDE LAYERS, I.E.E.E. transactions on electron devices, 45(11), 1998, pp. 2329-2334
In this work we have studied soft breakdown (SED) in capacitors and nM
OSFET's with 4.5-nm oxide thickness. It is shown that for larger area
devices gate current and substrate current as a function of the gate v
oltage after SED are stable and unique curves, but for smaller area de
,ices both currents become lower and unstable. This difference can be
explained by the different energy available for discharging in the SBD
path. It is shown that the SBD detection strongly depends on the test
structure area. In nMOSFET's for positive gate polarity, the large in
crease in the substrate current at the SBD moment is proposed as a sen
sitive SBD detector. Two level fluctuations in the gate current are in
vestigated at different voltages and are explained by means of a model
where electron capture-emission in the traps of the SBD path induces
local field fluctuations causing variations in the tunneling rate acro
ss the oxide. In the substrate current directly correlated two-level f
luctuations are observed.