An empirical expression for the direct tunneling (DT) current is obtained.This expression can be used to calculate the DT current for nMOSFETs with ultra thin oxide when the oxide thickness is considered as an adjustable parameter.The results have good agreement with the experimental data.And the oxide thickness obtained is less than the value acquired from the capacitance voltage( C V )method.
The degradation of MOS transistor operation due to soft breakdown of the gate oxide is studied.Important transistor parameters are monitored under homogeneous stress at different temperature until the soft breakdown occurred.The output and transfer characteristic have small change after soft breakdown as the degradations of drain current and threshold voltage is continuous.However,the increment of gate leakage current increases abruptly after the soft breakdown.The analysis to the increment of gate leakage current after the soft breakdown shows mechanism of similar Fowler Nordheim(FN) tunneling current.
