Extraction of trap densities in Al:HfO2 MIM capacitors using voltage ramp stress measurements

We present an experimental method to directly evaluate the oxide trap densities in TiN/Al:HfO/TiN capacitors from the low-field current hysteresis in voltage-ramp-stress (VRS) measurements. The extracted densities of deep electron traps are in the 1013 cm−2 range and virtually independent of the Al-doping concentration in HfO (ranging from 2% to 20%). These results indicate that the trapping sites are intrinsic and may be related to polaronic states in disordered HfO. Regarding reproducibility and stability, the measurements were consistent across all samples, except for those with low Al doping, which exhibited increased leakage and degradation likely due to partial crystallization. In degraded samples, conductive paths formed after electrical stress confine the leakage, limiting the sensitivity of the method to local trap densities adjacent to the leakage path.