The different charge trapping materials HfO2, HfAlO and Al2O3 have been compared electrically in metal-oxide-semiconductor capacitors with fixed Al2O3 tunneling and blocking layers and Pd-electrode. The capacitance-voltage hysteresis window, memory window, and stress-time dependent flat-band voltage shift increase with increasing the relative content of HfO2 in the charge trapping layer under the same measurement conditions. After programming at + 17 V for 0.1 s and erasing at - 17 V for 0.1 s, successively, the resulting memory window increases from 0.4 V to 3.8 V with increasing the content of HfO2 from 0% (Al2O3) to 100% (HfO2). However, the charge retention of the capacitors gradually worsens in the sequence of Al2O3, HfAlO and HfO2, which accords with the leakage characteristics of the capacitors. Our results reveal that HfAlO (A:H = 1:1) is a more promising charge trapping material than HfO2 and Al2O3 for polysilicon-oxide-nitride-oxide-silicon type memory applications. This is attributed to enough charge storage capacity, high thermal stability and medium dielectric constant. (c) 2012 Elsevier B.V. All rights reserved.