Performance Improvement in Charge-Trap Flash Memory Using Lanthanum-Based High-k Blocking Oxide

Abstract

Lanthanum-based high-kappa dielectrics (LaAlO(x) and LaHfO(x)) are systematically investigated as blocking oxide in charge-trap-type Flash memory devices. Compared to Al(2)O(3) blocking oxide, LaAlO(x) 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 LaHfO(x), 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.