Relaxation Behavior and Breakdown Mechanisms of Nanocrystals Embedded Zr-doped HfO2 High-k Thin Films for Nonvolatile Memories

摘要

Semiconducting or metallic nanocrystals embedded high-k films have been investigated. They showed promising nonvolatile memory characteristics, such as low leakage currents, large charge storage capacities, and long retention times. Reliability of four different kinds of nanocrystals, i.e., nc- Ru, -ITO, -Si and -ZnO, embedded Zr-doped HfO_2 high-k dielectrics have been studied. All of them have higher relaxation currents than the non-embedded high-k film has. The decay rate of the relaxation current is in the order of nc-ZnO > nc-ITO > nc-Si > nc-Ru. When the relaxation currents of the nanocrystals embedded samples were fitted to the Curie-von Schweidler law, the n values were between 0.54 and 0.77, which are much lower than that of the non embedded high-k sample. The nanocrystals retain charges in two different states, i.e., deeply and loosely trapped. The ratio of these two types of charges was estimated. The charge storage capacity and holding strength are strongly influenced by the type of material of the embedded nanocrystals. The nc-ZnO embedded film holds trapped charges longer than other embedded films do. The ramp-relax result indicates that the breakdown of the embedded film came from the breakdown of the bulk high-k film. The type of nanocrystal material influences the breakdown strength.