Trade-off relationship of size and density of platinum nanocrystal in nonvolatile memory characteristics

The replacement of metal nanocrystal (NC)-based nonvolatile memories (NVMs) with polycrystalline silicon floating-gate memories is very attractive, since they demonstrate superior capability of charge localization and a reduction in cell-to-cell interference. Varying the size (ranging from 15.1 to 55.2 nm) and density (from 5.6 × 10¹¹ to 3.2 × 10¹⁰cm ^-2) of the metal NC affects the entire memory properties such as the charging/discharging process, retention characteristic, and charge storage capability. Here, we investigated the effects of the size and density of platinum (Pt) NCs on the aforementioned memory characteristics by fabricating Pt-NC-embedded metal oxide semiconductor (MOS) capacitors using a direct self-assemble method. The flatband voltage shift, a measure of charge storage capability for NC-based NVMs, increased from 5.75 to 13.05 V as the mean size of the NCs was varied from 15.1 to 55.2 nm, which was relatively higher than that of other NC-based NVMs. Our studies revealed that the flatband voltage shift depends on not only the size and density of the NCs, but also the tunneling probability of the electrons, which is closely related to the applied electric field at a tunneling oxide. The relationships among the flatband voltage shift, the size and density of the NCs, and the applied electric field, which are revealed in this study, can be generally applicable to other NVMs based on various metal and semiconducting NCs.