Metal-oxide-nitride-oxide-silicon (MONOS) type memory devices with TaN/HfN gate and a high dielectric constant (high-k) charge trapping layer were experimentally realized by employing a SiO2/high-k/SiO2 structure that used Al2O3, HfO2, or HfAlO films, instead of Si3N4 film. The charge storage and retention characteristics of capacitors with Al2O3, HfO2, or HfAlO as the charge storage layer are compared to conventional MONOS (Si3N4 film) capacitors. Mixing 10 atom % of Al2O3 with 90 atom % of HfO2 to form HfAlO improves the charge retention capability of HfO2 without severely degrading its programming speed. Unlike conventional MONOS memory devices, HfAlO devices also exhibit better resistance to over-erase. The differences in the program/erase characteristics and the charge storage capability between the different structures are discussed. (C) 2004 The Electrochemical Society.