Abstract

We investigate the use of HfO2 based high-k materials as inter-gate dielectric in hybrid floating gate based memory cells for planar NAND flash. The incorporation of Al or Gd in the HfO2 allows reaching higher k values as compared with pure HfO2 through different crystalline characteritics. However, a difficult compromise is to be found between the k value and low leakage due to grain boudaries in a material with large crystalline proportions. Hence, HfGdO reaches a k value as high as 23 but shows important leakage that translates into early program saturation and room temperature charge loss. The HfAlO has more moderate k of similar to 16 but shows lower leakage leading to improved device performances. Finally, a three layer stack where a high-k HfAlO layer is encapsulated into Al2O3 thinner layers shows overall best compromise in terms of program/erase window and retention.