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 120 degrees C, particularly at 85 degrees C. 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.