Influence of the thickness of the tunnel layer on the charging characteristics of Si nanocrystals embedded in an ultra-thin SiO2 layer

In this paper, we have studied the effect of the thickness of the initial SiO2 layer (5-7 nm) on the charge and discharge properties of a 2D array of Si nanoparticles embedded in these SiO2 layers fabricated by ultra-low-energy ion implantation (ULE-II) and annealing. The structural characteristics of these nanocrystal-based memories (position of the nanocrystals with respect to the electrodes, size and surface density of the particles in the plane) were studied by transmission electron microscopy (TEM) and energy filtered TEM (EF-TEM). Electrical characterizations were performed at room temperature using a nano-MOS capacitor to be able to address only a few nanoparticles (nps). EFTEM gives the measurements of oxide thickness, injection, control and rips distances, size and density. I-V and I-t measurements exhibit current peaks and random telegraph signal fluctuations that can be interpreted as due to quantized charging of the rips and to some electrostatic interactions between the trapped charges and the tunnelling current. We have shown that these characteristics strongly vary with the initial oxide thickness, exhibiting several charging/discharging events for the 7-nm-thick layer while charging events prevail in the case of 5-nm-thick layer. These results indicate that the probability of discharging phenomena is reduced when the tunnel layer thickness decreases. (C) 2007 Elsevier B.V. All rights reserved.