A Critical Gate Voltage Triggering Irreversible Gate Dielectric Degradation

Using a multiple-stage constant-voltage stress (M-CVS) methodology, a critical gate voltage (V
_crit
) is found to demarcate the post-breakdown (BD) gate leakage current (I
_g
) evolution. For a gate voltage (V
_g
) < V
_crit
, I
_g
digitally fluctuates with no apparent net increase. For V
_g
> V
_crit
, I
_g
rapidly evolves into a stable high leakage state. V
_crit
is found to decrease with decreasing oxide thickness (T
_ox
), implying that it has a significant impact on I
_g
degradation rate (dl
_g
/dt) (Lombardo, 2003) at nominal operating voltages.