HfOz with EOT of 14A shows soft and hard breakdown behaviors which consist of different Weibull distributions, area scaling factors, and acceleration factors. Thickness dependence of Hf02 Weibull slope p indicates that the breakdown mechanism of Hf02 is intrinsic. Similar to SiOz, steeper voltage acceleration factor of HfO2 has been observed as thickness decreases. Unipolar AC voltage stress on MOS capacitors results in larger lifetime compared to constant voltage stress. This may be due to lower overall charge trapping as a result of short "on time" compared to the transition time and charge detrapping during the off period. The higher the frequency of the AC stress, the longer time-tobreakdown.
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