In this paper, we have performed further investigations and deepened our understanding of Polymer Resistive Random Access Memory devices (PoRRAM) on silicon substrate. Organic thin films based on blend of fullerene (C60) molecules and poly-methyl-methacrylate resist (PMMA) were analyzed from a material and electrical point of views. We have enlightened first the necessity of thermal treatment on the nano-composite layer in order to obtain memory effect in the device. Indeed from I-V measurements, only devices that had a thermal activation exhibited the hysteresis phenomenon, characteristic of the memory effect. The impact of thermal annealing has been investigated by morphological analysis (AFM and confocal microscopy) before and after thermal treatment. This process step induced the C60 molecules aggregation in the polymer matrix. The morphological study of these aggregates coupled with electrical measurements allowed us to determine the influence of aggregation on the electrical behavior. Due to their flexibility, this organic memories based on PMMA:C60 nanocomposites show a strong potential for an adaptation on plastic substrate.