The charge retention characteristics of metal nanocrystal (MNC) and semiconductor nanocrystal (SNQ memory devices are comparatively studied in this paper. A charge retention model is proposed, taking into account the quantum confinement effect, to account for the better retention characteristics of metal nanocrystal memory observed in the experiment. Simulation results are in good agreement with experimental data, which confirms the validity of this model. The impact of the nanocrystal size, tunneling dielectric materials (especially high-K dielectrics), and tunneling dielectric thickness on the retention characteristics are all investigated for both the metal nanocrystals and the semiconductor nanocrystals. (c) 2007 Elsevier Ltd. All rights reserved.