Single-Electron Program/Erase Tunnel Events in Nanocrystal Memories

This paper reports on the observation of single/few electron tunnel events at room temperature from silicon dots to the channel and reverse through a thin tunnel oxide in submicron nanocrystal memory cells. The events correspond to jumps in the drain current measured in the subthreshold regime under fixed bias conditions. The observed jumps are translated in term of threshold voltage variation and a procedure for extracting the threshold voltage shift associated to these events is proposed. A deeper investigation of the impact of these tunnel phenomena and a quantitative explanation are given in the framework of a phenomenological model with one or three free parameters, depending on the assumptions. The proposed model studies, by means of a new percolation approach, the correlation between area controlled by a single trapped electron and the appearance of single-electron events