Performance Improvement in Charge-Trap Flash Memory Using Lanthanum-Based High- $\kappa$ Blocking Oxide

Lanthanum-based high-kappa dielectrics ( LaAlOx and LaHfOx) are systematically investigated as blocking oxide in charge-trap-type flash memory devices. Compared to Al₂O₃ blocking oxide, LaAlOx not only exhibits faster program speed, wider V _th window, and more robustness to voltage stress but also has better retention performance when the temperature is below 120degC, particularly at 85degC . In contrast, although further improvements in V _th window and robustness are achieved using a higher permittivity dielectric LaHfOx, its retention performance is poor. It is found that the retention property is critically determined by the conduction band offset of a blocking oxide. This is caused by the shallow trapping energy depth inside the nitride which is calculated to be 0.6-0.75 eV below the conduction band edge.